Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 4786 insertions, 0 deletions

diff --git a/third_party/libwebrtc/pc/media_session_unittest.cc b/third_party/libwebrtc/pc/media_session_unittest.cc
new file mode 100644
index 0000000000..8f38f6a1b4
--- /dev/null
+++ b/third_party/libwebrtc/pc/media_session_unittest.cc
@@ -0,0 +1,4786 @@
+/*
+ *  Copyright 2004 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "pc/media_session.h"
+
+#include <stddef.h>
+
+#include <algorithm>
+#include <cstdint>
+#include <map>
+#include <memory>
+#include <string>
+#include <tuple>
+#include <vector>
+
+#include "absl/algorithm/container.h"
+#include "absl/strings/match.h"
+#include "absl/strings/string_view.h"
+#include "api/candidate.h"
+#include "api/crypto_params.h"
+#include "media/base/codec.h"
+#include "media/base/media_constants.h"
+#include "media/base/test_utils.h"
+#include "media/sctp/sctp_transport_internal.h"
+#include "p2p/base/p2p_constants.h"
+#include "p2p/base/transport_description.h"
+#include "p2p/base/transport_info.h"
+#include "pc/media_protocol_names.h"
+#include "pc/rtp_media_utils.h"
+#include "rtc_base/arraysize.h"
+#include "rtc_base/checks.h"
+#include "rtc_base/fake_ssl_identity.h"
+#include "rtc_base/rtc_certificate.h"
+#include "rtc_base/ssl_identity.h"
+#include "rtc_base/ssl_stream_adapter.h"
+#include "rtc_base/string_encode.h"
+#include "rtc_base/strings/string_builder.h"
+#include "rtc_base/unique_id_generator.h"
+#include "test/gmock.h"
+#include "test/gtest.h"
+#include "test/scoped_key_value_config.h"
+
+#define ASSERT_CRYPTO(cd, s, cs)      \
+  ASSERT_EQ(s, cd->cryptos().size()); \
+  ASSERT_EQ(cs, cd->cryptos()[0].cipher_suite)
+
+typedef std::vector<cricket::Candidate> Candidates;
+
+using cricket::AudioCodec;
+using cricket::AudioContentDescription;
+using cricket::ContentInfo;
+using cricket::CryptoParamsVec;
+using cricket::GetFirstAudioContent;
+using cricket::GetFirstAudioContentDescription;
+using cricket::GetFirstDataContent;
+using cricket::GetFirstVideoContent;
+using cricket::GetFirstVideoContentDescription;
+using cricket::kAutoBandwidth;
+using cricket::MEDIA_TYPE_AUDIO;
+using cricket::MEDIA_TYPE_DATA;
+using cricket::MEDIA_TYPE_VIDEO;
+using cricket::MediaContentDescription;
+using cricket::MediaDescriptionOptions;
+using cricket::MediaProtocolType;
+using cricket::MediaSessionDescriptionFactory;
+using cricket::MediaSessionOptions;
+using cricket::MediaType;
+using cricket::RidDescription;
+using cricket::RidDirection;
+using cricket::SctpDataContentDescription;
+using cricket::SEC_DISABLED;
+using cricket::SEC_ENABLED;
+using cricket::SEC_REQUIRED;
+using cricket::SessionDescription;
+using cricket::SimulcastDescription;
+using cricket::SimulcastLayer;
+using cricket::SimulcastLayerList;
+using cricket::SsrcGroup;
+using cricket::StreamParams;
+using cricket::StreamParamsVec;
+using cricket::TransportDescription;
+using cricket::TransportDescriptionFactory;
+using cricket::TransportInfo;
+using cricket::VideoCodec;
+using cricket::VideoContentDescription;
+using rtc::kCsAeadAes128Gcm;
+using rtc::kCsAeadAes256Gcm;
+using rtc::kCsAesCm128HmacSha1_32;
+using rtc::kCsAesCm128HmacSha1_80;
+using rtc::UniqueRandomIdGenerator;
+using ::testing::Contains;
+using ::testing::Each;
+using ::testing::ElementsAre;
+using ::testing::ElementsAreArray;
+using ::testing::Eq;
+using ::testing::Field;
+using ::testing::IsEmpty;
+using ::testing::IsFalse;
+using ::testing::Ne;
+using ::testing::Not;
+using ::testing::Pointwise;
+using ::testing::SizeIs;
+using webrtc::RtpExtension;
+using webrtc::RtpTransceiverDirection;
+
+static const AudioCodec kAudioCodecs1[] = {
+    AudioCodec(103, "ISAC", 16000, -1, 1),
+    AudioCodec(102, "iLBC", 8000, 13300, 1),
+    AudioCodec(0, "PCMU", 8000, 64000, 1),
+    AudioCodec(8, "PCMA", 8000, 64000, 1),
+    AudioCodec(117, "red", 8000, 0, 1),
+    AudioCodec(107, "CN", 48000, 0, 1)};
+
+static const AudioCodec kAudioCodecs2[] = {
+    AudioCodec(126, "foo", 16000, 22000, 1),
+    AudioCodec(0, "PCMU", 8000, 64000, 1),
+    AudioCodec(127, "iLBC", 8000, 13300, 1),
+};
+
+static const AudioCodec kAudioCodecsAnswer[] = {
+    AudioCodec(102, "iLBC", 8000, 13300, 1),
+    AudioCodec(0, "PCMU", 8000, 64000, 1),
+};
+
+static const VideoCodec kVideoCodecs1[] = {VideoCodec(96, "H264-SVC"),
+                                           VideoCodec(97, "H264")};
+
+static const VideoCodec kVideoCodecs1Reverse[] = {VideoCodec(97, "H264"),
+                                                  VideoCodec(96, "H264-SVC")};
+
+static const VideoCodec kVideoCodecs2[] = {VideoCodec(126, "H264"),
+                                           VideoCodec(127, "H263")};
+
+static const VideoCodec kVideoCodecsAnswer[] = {VideoCodec(97, "H264")};
+
+static const RtpExtension kAudioRtpExtension1[] = {
+    RtpExtension("urn:ietf:params:rtp-hdrext:ssrc-audio-level", 8),
+    RtpExtension("http://google.com/testing/audio_something", 10),
+};
+
+static const RtpExtension kAudioRtpExtensionEncrypted1[] = {
+    RtpExtension("urn:ietf:params:rtp-hdrext:ssrc-audio-level", 8),
+    RtpExtension("http://google.com/testing/audio_something", 10),
+    RtpExtension("urn:ietf:params:rtp-hdrext:ssrc-audio-level", 12, true),
+    RtpExtension("http://google.com/testing/audio_something", 11, true),
+};
+
+static const RtpExtension kAudioRtpExtension2[] = {
+    RtpExtension("urn:ietf:params:rtp-hdrext:ssrc-audio-level", 2),
+    RtpExtension("http://google.com/testing/audio_something_else", 8),
+    RtpExtension("http://google.com/testing/both_audio_and_video", 7),
+};
+
+static const RtpExtension kAudioRtpExtension3[] = {
+    RtpExtension("http://google.com/testing/audio_something", 2),
+    RtpExtension("http://google.com/testing/both_audio_and_video", 3),
+};
+
+static const RtpExtension kAudioRtpExtension3ForEncryption[] = {
+    RtpExtension("http://google.com/testing/audio_something", 2),
+    // Use RTP extension that supports encryption.
+    RtpExtension("urn:ietf:params:rtp-hdrext:toffset", 3),
+};
+
+static const RtpExtension kAudioRtpExtension3ForEncryptionOffer[] = {
+    RtpExtension("http://google.com/testing/audio_something", 2),
+    RtpExtension("urn:ietf:params:rtp-hdrext:toffset", 3),
+    RtpExtension("http://google.com/testing/audio_something", 14, true),
+    RtpExtension("urn:ietf:params:rtp-hdrext:toffset", 13, true),
+};
+
+static const RtpExtension kVideoRtpExtension3ForEncryptionOffer[] = {
+    RtpExtension("http://google.com/testing/video_something", 4),
+    RtpExtension("urn:ietf:params:rtp-hdrext:toffset", 3),
+    RtpExtension("http://google.com/testing/video_something", 12, true),
+    RtpExtension("urn:ietf:params:rtp-hdrext:toffset", 13, true),
+};
+
+static const RtpExtension kAudioRtpExtensionAnswer[] = {
+    RtpExtension("urn:ietf:params:rtp-hdrext:ssrc-audio-level", 8),
+};
+
+static const RtpExtension kAudioRtpExtensionEncryptedAnswer[] = {
+    RtpExtension("urn:ietf:params:rtp-hdrext:ssrc-audio-level", 12, true),
+};
+
+static const RtpExtension kVideoRtpExtension1[] = {
+    RtpExtension("urn:ietf:params:rtp-hdrext:toffset", 14),
+    RtpExtension("http://google.com/testing/video_something", 13),
+};
+
+static const RtpExtension kVideoRtpExtensionEncrypted1[] = {
+    RtpExtension("urn:ietf:params:rtp-hdrext:toffset", 14),
+    RtpExtension("http://google.com/testing/video_something", 13),
+    RtpExtension("urn:ietf:params:rtp-hdrext:toffset", 9, true),
+    RtpExtension("http://google.com/testing/video_something", 7, true),
+};
+
+static const RtpExtension kVideoRtpExtension2[] = {
+    RtpExtension("urn:ietf:params:rtp-hdrext:toffset", 2),
+    RtpExtension("http://google.com/testing/video_something_else", 14),
+    RtpExtension("http://google.com/testing/both_audio_and_video", 7),
+};
+
+static const RtpExtension kVideoRtpExtension3[] = {
+    RtpExtension("http://google.com/testing/video_something", 4),
+    RtpExtension("http://google.com/testing/both_audio_and_video", 5),
+};
+
+static const RtpExtension kVideoRtpExtension3ForEncryption[] = {
+    RtpExtension("http://google.com/testing/video_something", 4),
+    // Use RTP extension that supports encryption.
+    RtpExtension("urn:ietf:params:rtp-hdrext:toffset", 5),
+};
+
+static const RtpExtension kVideoRtpExtensionAnswer[] = {
+    RtpExtension("urn:ietf:params:rtp-hdrext:toffset", 14),
+};
+
+static const RtpExtension kVideoRtpExtensionEncryptedAnswer[] = {
+    RtpExtension("urn:ietf:params:rtp-hdrext:toffset", 9, true),
+};
+
+static const RtpExtension kRtpExtensionTransportSequenceNumber01[] = {
+    RtpExtension("http://www.ietf.org/id/"
+                 "draft-holmer-rmcat-transport-wide-cc-extensions-01",
+                 1),
+};
+
+static const RtpExtension kRtpExtensionTransportSequenceNumber01And02[] = {
+    RtpExtension("http://www.ietf.org/id/"
+                 "draft-holmer-rmcat-transport-wide-cc-extensions-01",
+                 1),
+    RtpExtension(
+        "http://www.webrtc.org/experiments/rtp-hdrext/transport-wide-cc-02",
+        2),
+};
+
+static const RtpExtension kRtpExtensionTransportSequenceNumber02[] = {
+    RtpExtension(
+        "http://www.webrtc.org/experiments/rtp-hdrext/transport-wide-cc-02",
+        2),
+};
+
+static const RtpExtension kRtpExtensionGenericFrameDescriptorUri00[] = {
+    RtpExtension("http://www.webrtc.org/experiments/rtp-hdrext/"
+                 "generic-frame-descriptor-00",
+                 3),
+};
+
+static const uint32_t kSimulcastParamsSsrc[] = {10, 11, 20, 21, 30, 31};
+static const uint32_t kSimSsrc[] = {10, 20, 30};
+static const uint32_t kFec1Ssrc[] = {10, 11};
+static const uint32_t kFec2Ssrc[] = {20, 21};
+static const uint32_t kFec3Ssrc[] = {30, 31};
+
+static const char kMediaStream1[] = "stream_1";
+static const char kMediaStream2[] = "stream_2";
+static const char kVideoTrack1[] = "video_1";
+static const char kVideoTrack2[] = "video_2";
+static const char kAudioTrack1[] = "audio_1";
+static const char kAudioTrack2[] = "audio_2";
+static const char kAudioTrack3[] = "audio_3";
+
+static const char* kMediaProtocols[] = {"RTP/AVP", "RTP/SAVP", "RTP/AVPF",
+                                        "RTP/SAVPF"};
+static const char* kMediaProtocolsDtls[] = {
+    "TCP/TLS/RTP/SAVPF", "TCP/TLS/RTP/SAVP", "UDP/TLS/RTP/SAVPF",
+    "UDP/TLS/RTP/SAVP"};
+
+// SRTP cipher name negotiated by the tests. This must be updated if the
+// default changes.
+static const char* kDefaultSrtpCryptoSuite = kCsAesCm128HmacSha1_80;
+static const char* kDefaultSrtpCryptoSuiteGcm = kCsAeadAes256Gcm;
+
+// These constants are used to make the code using "AddMediaDescriptionOptions"
+// more readable.
+static constexpr bool kStopped = true;
+static constexpr bool kActive = false;
+
+static bool IsMediaContentOfType(const ContentInfo* content,
+                                 MediaType media_type) {
+  RTC_DCHECK(content);
+  return content->media_description()->type() == media_type;
+}
+
+static RtpTransceiverDirection GetMediaDirection(const ContentInfo* content) {
+  RTC_DCHECK(content);
+  return content->media_description()->direction();
+}
+
+static void AddRtxCodec(const VideoCodec& rtx_codec,
+                        std::vector<VideoCodec>* codecs) {
+  ASSERT_FALSE(cricket::FindCodecById(*codecs, rtx_codec.id));
+  codecs->push_back(rtx_codec);
+}
+
+template <class T>
+static std::vector<std::string> GetCodecNames(const std::vector<T>& codecs) {
+  std::vector<std::string> codec_names;
+  codec_names.reserve(codecs.size());
+  for (const auto& codec : codecs) {
+    codec_names.push_back(codec.name);
+  }
+  return codec_names;
+}
+
+// This is used for test only. MIDs are not the identification of the
+// MediaDescriptionOptions since some end points may not support MID and the SDP
+// may not contain 'mid'.
+std::vector<MediaDescriptionOptions>::iterator FindFirstMediaDescriptionByMid(
+    const std::string& mid,
+    MediaSessionOptions* opts) {
+  return absl::c_find_if(
+      opts->media_description_options,
+      [&mid](const MediaDescriptionOptions& t) { return t.mid == mid; });
+}
+
+std::vector<MediaDescriptionOptions>::const_iterator
+FindFirstMediaDescriptionByMid(const std::string& mid,
+                               const MediaSessionOptions& opts) {
+  return absl::c_find_if(
+      opts.media_description_options,
+      [&mid](const MediaDescriptionOptions& t) { return t.mid == mid; });
+}
+
+// Add a media section to the `session_options`.
+static void AddMediaDescriptionOptions(MediaType type,
+                                       const std::string& mid,
+                                       RtpTransceiverDirection direction,
+                                       bool stopped,
+                                       MediaSessionOptions* opts) {
+  opts->media_description_options.push_back(
+      MediaDescriptionOptions(type, mid, direction, stopped));
+}
+
+static void AddAudioVideoSections(RtpTransceiverDirection direction,
+                                  MediaSessionOptions* opts) {
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio", direction, kActive,
+                             opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video", direction, kActive,
+                             opts);
+}
+
+static void AddDataSection(RtpTransceiverDirection direction,
+                           MediaSessionOptions* opts) {
+  AddMediaDescriptionOptions(MEDIA_TYPE_DATA, "data", direction, kActive, opts);
+}
+
+static void AttachSenderToMediaDescriptionOptions(
+    const std::string& mid,
+    MediaType type,
+    const std::string& track_id,
+    const std::vector<std::string>& stream_ids,
+    const std::vector<RidDescription>& rids,
+    const SimulcastLayerList& simulcast_layers,
+    int num_sim_layer,
+    MediaSessionOptions* session_options) {
+  auto it = FindFirstMediaDescriptionByMid(mid, session_options);
+  switch (type) {
+    case MEDIA_TYPE_AUDIO:
+      it->AddAudioSender(track_id, stream_ids);
+      break;
+    case MEDIA_TYPE_VIDEO:
+      it->AddVideoSender(track_id, stream_ids, rids, simulcast_layers,
+                         num_sim_layer);
+      break;
+    default:
+      RTC_DCHECK_NOTREACHED();
+  }
+}
+
+static void AttachSenderToMediaDescriptionOptions(
+    const std::string& mid,
+    MediaType type,
+    const std::string& track_id,
+    const std::vector<std::string>& stream_ids,
+    int num_sim_layer,
+    MediaSessionOptions* session_options) {
+  AttachSenderToMediaDescriptionOptions(mid, type, track_id, stream_ids, {},
+                                        SimulcastLayerList(), num_sim_layer,
+                                        session_options);
+}
+
+static void DetachSenderFromMediaSection(const std::string& mid,
+                                         const std::string& track_id,
+                                         MediaSessionOptions* session_options) {
+  std::vector<cricket::SenderOptions>& sender_options_list =
+      FindFirstMediaDescriptionByMid(mid, session_options)->sender_options;
+  auto sender_it =
+      absl::c_find_if(sender_options_list,
+                      [track_id](const cricket::SenderOptions& sender_options) {
+                        return sender_options.track_id == track_id;
+                      });
+  RTC_DCHECK(sender_it != sender_options_list.end());
+  sender_options_list.erase(sender_it);
+}
+
+// Helper function used to create a default MediaSessionOptions for Plan B SDP.
+// (https://tools.ietf.org/html/draft-uberti-rtcweb-plan-00).
+static MediaSessionOptions CreatePlanBMediaSessionOptions() {
+  MediaSessionOptions session_options;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &session_options);
+  return session_options;
+}
+
+// prefers GCM SDES crypto suites by removing non-GCM defaults.
+void PreferGcmCryptoParameters(CryptoParamsVec* cryptos) {
+  cryptos->erase(
+      std::remove_if(cryptos->begin(), cryptos->end(),
+                     [](const cricket::CryptoParams& crypto) {
+                       return crypto.cipher_suite != kCsAeadAes256Gcm &&
+                              crypto.cipher_suite != kCsAeadAes128Gcm;
+                     }),
+      cryptos->end());
+}
+
+// TODO(zhihuang): Most of these tests were written while MediaSessionOptions
+// was designed for Plan B SDP, where only one audio "m=" section and one video
+// "m=" section could be generated, and ordering couldn't be controlled. Many of
+// these tests may be obsolete as a result, and should be refactored or removed.
+class MediaSessionDescriptionFactoryTest : public ::testing::Test {
+ public:
+  MediaSessionDescriptionFactoryTest()
+      : tdf1_(field_trials),
+        tdf2_(field_trials),
+        f1_(&tdf1_, &ssrc_generator1),
+        f2_(&tdf2_, &ssrc_generator2) {
+    f1_.set_audio_codecs(MAKE_VECTOR(kAudioCodecs1),
+                         MAKE_VECTOR(kAudioCodecs1));
+    f1_.set_video_codecs(MAKE_VECTOR(kVideoCodecs1),
+                         MAKE_VECTOR(kVideoCodecs1));
+    f2_.set_audio_codecs(MAKE_VECTOR(kAudioCodecs2),
+                         MAKE_VECTOR(kAudioCodecs2));
+    f2_.set_video_codecs(MAKE_VECTOR(kVideoCodecs2),
+                         MAKE_VECTOR(kVideoCodecs2));
+    tdf1_.set_certificate(rtc::RTCCertificate::Create(
+        std::unique_ptr<rtc::SSLIdentity>(new rtc::FakeSSLIdentity("id1"))));
+    tdf2_.set_certificate(rtc::RTCCertificate::Create(
+        std::unique_ptr<rtc::SSLIdentity>(new rtc::FakeSSLIdentity("id2"))));
+  }
+
+  // Create a video StreamParamsVec object with:
+  // - one video stream with 3 simulcast streams and FEC,
+  StreamParamsVec CreateComplexVideoStreamParamsVec() {
+    SsrcGroup sim_group("SIM", MAKE_VECTOR(kSimSsrc));
+    SsrcGroup fec_group1("FEC", MAKE_VECTOR(kFec1Ssrc));
+    SsrcGroup fec_group2("FEC", MAKE_VECTOR(kFec2Ssrc));
+    SsrcGroup fec_group3("FEC", MAKE_VECTOR(kFec3Ssrc));
+
+    std::vector<SsrcGroup> ssrc_groups;
+    ssrc_groups.push_back(sim_group);
+    ssrc_groups.push_back(fec_group1);
+    ssrc_groups.push_back(fec_group2);
+    ssrc_groups.push_back(fec_group3);
+
+    StreamParams simulcast_params;
+    simulcast_params.id = kVideoTrack1;
+    simulcast_params.ssrcs = MAKE_VECTOR(kSimulcastParamsSsrc);
+    simulcast_params.ssrc_groups = ssrc_groups;
+    simulcast_params.cname = "Video_SIM_FEC";
+    simulcast_params.set_stream_ids({kMediaStream1});
+
+    StreamParamsVec video_streams;
+    video_streams.push_back(simulcast_params);
+
+    return video_streams;
+  }
+
+  bool CompareCryptoParams(const CryptoParamsVec& c1,
+                           const CryptoParamsVec& c2) {
+    if (c1.size() != c2.size())
+      return false;
+    for (size_t i = 0; i < c1.size(); ++i)
+      if (c1[i].tag != c2[i].tag || c1[i].cipher_suite != c2[i].cipher_suite ||
+          c1[i].key_params != c2[i].key_params ||
+          c1[i].session_params != c2[i].session_params)
+        return false;
+    return true;
+  }
+
+  // Returns true if the transport info contains "renomination" as an
+  // ICE option.
+  bool GetIceRenomination(const TransportInfo* transport_info) {
+    return absl::c_linear_search(transport_info->description.transport_options,
+                                 "renomination");
+  }
+
+  void TestTransportInfo(bool offer,
+                         const MediaSessionOptions& options,
+                         bool has_current_desc) {
+    const std::string current_audio_ufrag = "current_audio_ufrag";
+    const std::string current_audio_pwd = "current_audio_pwd";
+    const std::string current_video_ufrag = "current_video_ufrag";
+    const std::string current_video_pwd = "current_video_pwd";
+    const std::string current_data_ufrag = "current_data_ufrag";
+    const std::string current_data_pwd = "current_data_pwd";
+    std::unique_ptr<SessionDescription> current_desc;
+    std::unique_ptr<SessionDescription> desc;
+    if (has_current_desc) {
+      current_desc = std::make_unique<SessionDescription>();
+      current_desc->AddTransportInfo(TransportInfo(
+          "audio",
+          TransportDescription(current_audio_ufrag, current_audio_pwd)));
+      current_desc->AddTransportInfo(TransportInfo(
+          "video",
+          TransportDescription(current_video_ufrag, current_video_pwd)));
+      current_desc->AddTransportInfo(TransportInfo(
+          "data", TransportDescription(current_data_ufrag, current_data_pwd)));
+    }
+    if (offer) {
+      desc = f1_.CreateOffer(options, current_desc.get());
+    } else {
+      std::unique_ptr<SessionDescription> offer;
+      offer = f1_.CreateOffer(options, NULL);
+      desc = f1_.CreateAnswer(offer.get(), options, current_desc.get());
+    }
+    ASSERT_TRUE(desc.get() != NULL);
+    const TransportInfo* ti_audio = desc->GetTransportInfoByName("audio");
+    if (options.has_audio()) {
+      EXPECT_TRUE(ti_audio != NULL);
+      if (has_current_desc) {
+        EXPECT_EQ(current_audio_ufrag, ti_audio->description.ice_ufrag);
+        EXPECT_EQ(current_audio_pwd, ti_audio->description.ice_pwd);
+      } else {
+        EXPECT_EQ(static_cast<size_t>(cricket::ICE_UFRAG_LENGTH),
+                  ti_audio->description.ice_ufrag.size());
+        EXPECT_EQ(static_cast<size_t>(cricket::ICE_PWD_LENGTH),
+                  ti_audio->description.ice_pwd.size());
+      }
+      auto media_desc_options_it =
+          FindFirstMediaDescriptionByMid("audio", options);
+      EXPECT_EQ(
+          media_desc_options_it->transport_options.enable_ice_renomination,
+          GetIceRenomination(ti_audio));
+    } else {
+      EXPECT_TRUE(ti_audio == NULL);
+    }
+    const TransportInfo* ti_video = desc->GetTransportInfoByName("video");
+    if (options.has_video()) {
+      EXPECT_TRUE(ti_video != NULL);
+      auto media_desc_options_it =
+          FindFirstMediaDescriptionByMid("video", options);
+      if (options.bundle_enabled) {
+        EXPECT_EQ(ti_audio->description.ice_ufrag,
+                  ti_video->description.ice_ufrag);
+        EXPECT_EQ(ti_audio->description.ice_pwd, ti_video->description.ice_pwd);
+      } else {
+        if (has_current_desc) {
+          EXPECT_EQ(current_video_ufrag, ti_video->description.ice_ufrag);
+          EXPECT_EQ(current_video_pwd, ti_video->description.ice_pwd);
+        } else {
+          EXPECT_EQ(static_cast<size_t>(cricket::ICE_UFRAG_LENGTH),
+                    ti_video->description.ice_ufrag.size());
+          EXPECT_EQ(static_cast<size_t>(cricket::ICE_PWD_LENGTH),
+                    ti_video->description.ice_pwd.size());
+        }
+      }
+      EXPECT_EQ(
+          media_desc_options_it->transport_options.enable_ice_renomination,
+          GetIceRenomination(ti_video));
+    } else {
+      EXPECT_TRUE(ti_video == NULL);
+    }
+    const TransportInfo* ti_data = desc->GetTransportInfoByName("data");
+    if (options.has_data()) {
+      EXPECT_TRUE(ti_data != NULL);
+      if (options.bundle_enabled) {
+        EXPECT_EQ(ti_audio->description.ice_ufrag,
+                  ti_data->description.ice_ufrag);
+        EXPECT_EQ(ti_audio->description.ice_pwd, ti_data->description.ice_pwd);
+      } else {
+        if (has_current_desc) {
+          EXPECT_EQ(current_data_ufrag, ti_data->description.ice_ufrag);
+          EXPECT_EQ(current_data_pwd, ti_data->description.ice_pwd);
+        } else {
+          EXPECT_EQ(static_cast<size_t>(cricket::ICE_UFRAG_LENGTH),
+                    ti_data->description.ice_ufrag.size());
+          EXPECT_EQ(static_cast<size_t>(cricket::ICE_PWD_LENGTH),
+                    ti_data->description.ice_pwd.size());
+        }
+      }
+      auto media_desc_options_it =
+          FindFirstMediaDescriptionByMid("data", options);
+      EXPECT_EQ(
+          media_desc_options_it->transport_options.enable_ice_renomination,
+          GetIceRenomination(ti_data));
+
+    } else {
+      EXPECT_TRUE(ti_data == NULL);
+    }
+  }
+
+  void TestCryptoWithBundle(bool offer) {
+    f1_.set_secure(SEC_ENABLED);
+    MediaSessionOptions options;
+    AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &options);
+    std::unique_ptr<SessionDescription> ref_desc;
+    std::unique_ptr<SessionDescription> desc;
+    if (offer) {
+      options.bundle_enabled = false;
+      ref_desc = f1_.CreateOffer(options, NULL);
+      options.bundle_enabled = true;
+      desc = f1_.CreateOffer(options, ref_desc.get());
+    } else {
+      options.bundle_enabled = true;
+      ref_desc = f1_.CreateOffer(options, NULL);
+      desc = f1_.CreateAnswer(ref_desc.get(), options, NULL);
+    }
+    ASSERT_TRUE(desc);
+    const cricket::MediaContentDescription* audio_media_desc =
+        desc->GetContentDescriptionByName("audio");
+    ASSERT_TRUE(audio_media_desc);
+    const cricket::MediaContentDescription* video_media_desc =
+        desc->GetContentDescriptionByName("video");
+    ASSERT_TRUE(video_media_desc);
+    EXPECT_TRUE(CompareCryptoParams(audio_media_desc->cryptos(),
+                                    video_media_desc->cryptos()));
+    EXPECT_EQ(1u, audio_media_desc->cryptos().size());
+    EXPECT_EQ(kDefaultSrtpCryptoSuite,
+              audio_media_desc->cryptos()[0].cipher_suite);
+
+    // Verify the selected crypto is one from the reference audio
+    // media content.
+    const cricket::MediaContentDescription* ref_audio_media_desc =
+        ref_desc->GetContentDescriptionByName("audio");
+    bool found = false;
+    for (size_t i = 0; i < ref_audio_media_desc->cryptos().size(); ++i) {
+      if (ref_audio_media_desc->cryptos()[i].Matches(
+              audio_media_desc->cryptos()[0])) {
+        found = true;
+        break;
+      }
+    }
+    EXPECT_TRUE(found);
+  }
+
+  // This test that the audio and video media direction is set to
+  // `expected_direction_in_answer` in an answer if the offer direction is set
+  // to `direction_in_offer` and the answer is willing to both send and receive.
+  void TestMediaDirectionInAnswer(
+      RtpTransceiverDirection direction_in_offer,
+      RtpTransceiverDirection expected_direction_in_answer) {
+    MediaSessionOptions offer_opts;
+    AddAudioVideoSections(direction_in_offer, &offer_opts);
+
+    std::unique_ptr<SessionDescription> offer =
+        f1_.CreateOffer(offer_opts, NULL);
+    ASSERT_TRUE(offer.get() != NULL);
+    ContentInfo* ac_offer = offer->GetContentByName("audio");
+    ASSERT_TRUE(ac_offer != NULL);
+    ContentInfo* vc_offer = offer->GetContentByName("video");
+    ASSERT_TRUE(vc_offer != NULL);
+
+    MediaSessionOptions answer_opts;
+    AddAudioVideoSections(RtpTransceiverDirection::kSendRecv, &answer_opts);
+    std::unique_ptr<SessionDescription> answer =
+        f2_.CreateAnswer(offer.get(), answer_opts, NULL);
+    const AudioContentDescription* acd_answer =
+        GetFirstAudioContentDescription(answer.get());
+    EXPECT_EQ(expected_direction_in_answer, acd_answer->direction());
+    const VideoContentDescription* vcd_answer =
+        GetFirstVideoContentDescription(answer.get());
+    EXPECT_EQ(expected_direction_in_answer, vcd_answer->direction());
+  }
+
+  bool VerifyNoCNCodecs(const cricket::ContentInfo* content) {
+    RTC_DCHECK(content);
+    RTC_CHECK(content->media_description());
+    const cricket::AudioContentDescription* audio_desc =
+        content->media_description()->as_audio();
+    RTC_CHECK(audio_desc);
+    for (const cricket::AudioCodec& codec : audio_desc->codecs()) {
+      if (codec.name == "CN") {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  void TestVideoGcmCipher(bool gcm_offer, bool gcm_answer) {
+    MediaSessionOptions offer_opts;
+    AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &offer_opts);
+    offer_opts.crypto_options.srtp.enable_gcm_crypto_suites = gcm_offer;
+
+    MediaSessionOptions answer_opts;
+    AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &answer_opts);
+    answer_opts.crypto_options.srtp.enable_gcm_crypto_suites = gcm_answer;
+
+    f1_.set_secure(SEC_ENABLED);
+    f2_.set_secure(SEC_ENABLED);
+    std::unique_ptr<SessionDescription> offer =
+        f1_.CreateOffer(offer_opts, NULL);
+    ASSERT_TRUE(offer.get() != NULL);
+    if (gcm_offer && gcm_answer) {
+      for (cricket::ContentInfo& content : offer->contents()) {
+        auto cryptos = content.media_description()->cryptos();
+        PreferGcmCryptoParameters(&cryptos);
+        content.media_description()->set_cryptos(cryptos);
+      }
+    }
+    std::unique_ptr<SessionDescription> answer =
+        f2_.CreateAnswer(offer.get(), answer_opts, NULL);
+    const ContentInfo* ac = answer->GetContentByName("audio");
+    const ContentInfo* vc = answer->GetContentByName("video");
+    ASSERT_TRUE(ac != NULL);
+    ASSERT_TRUE(vc != NULL);
+    EXPECT_EQ(MediaProtocolType::kRtp, ac->type);
+    EXPECT_EQ(MediaProtocolType::kRtp, vc->type);
+    const AudioContentDescription* acd = ac->media_description()->as_audio();
+    const VideoContentDescription* vcd = vc->media_description()->as_video();
+    EXPECT_EQ(MEDIA_TYPE_AUDIO, acd->type());
+    EXPECT_THAT(acd->codecs(), ElementsAreArray(kAudioCodecsAnswer));
+    EXPECT_EQ(kAutoBandwidth, acd->bandwidth());  // negotiated auto bw
+    EXPECT_EQ(0U, acd->first_ssrc());             // no sender is attached
+    EXPECT_TRUE(acd->rtcp_mux());                 // negotiated rtcp-mux
+    if (gcm_offer && gcm_answer) {
+      ASSERT_CRYPTO(acd, 1U, kDefaultSrtpCryptoSuiteGcm);
+    } else {
+      ASSERT_CRYPTO(acd, 1U, kDefaultSrtpCryptoSuite);
+    }
+    EXPECT_EQ(MEDIA_TYPE_VIDEO, vcd->type());
+    EXPECT_THAT(vcd->codecs(), ElementsAreArray(kVideoCodecsAnswer));
+    EXPECT_EQ(0U, vcd->first_ssrc());  // no sender is attached
+    EXPECT_TRUE(vcd->rtcp_mux());      // negotiated rtcp-mux
+    if (gcm_offer && gcm_answer) {
+      ASSERT_CRYPTO(vcd, 1U, kDefaultSrtpCryptoSuiteGcm);
+    } else {
+      ASSERT_CRYPTO(vcd, 1U, kDefaultSrtpCryptoSuite);
+    }
+    EXPECT_EQ(cricket::kMediaProtocolSavpf, vcd->protocol());
+  }
+
+  void TestTransportSequenceNumberNegotiation(
+      const cricket::RtpHeaderExtensions& local,
+      const cricket::RtpHeaderExtensions& offered,
+      const cricket::RtpHeaderExtensions& expectedAnswer) {
+    MediaSessionOptions opts;
+    AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+    SetAudioVideoRtpHeaderExtensions(offered, offered, &opts);
+    std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+    ASSERT_TRUE(offer.get() != NULL);
+    SetAudioVideoRtpHeaderExtensions(local, local, &opts);
+    std::unique_ptr<SessionDescription> answer =
+        f2_.CreateAnswer(offer.get(), opts, NULL);
+
+    EXPECT_EQ(
+        expectedAnswer,
+        GetFirstAudioContentDescription(answer.get())->rtp_header_extensions());
+    EXPECT_EQ(
+        expectedAnswer,
+        GetFirstVideoContentDescription(answer.get())->rtp_header_extensions());
+  }
+
+  std::vector<webrtc::RtpHeaderExtensionCapability>
+  HeaderExtensionCapabilitiesFromRtpExtensions(
+      cricket::RtpHeaderExtensions extensions) {
+    std::vector<webrtc::RtpHeaderExtensionCapability> capabilities;
+    for (const auto& extension : extensions) {
+      webrtc::RtpHeaderExtensionCapability capability(
+          extension.uri, extension.id,
+          webrtc::RtpTransceiverDirection::kSendRecv);
+      capabilities.push_back(capability);
+    }
+    return capabilities;
+  }
+
+  void SetAudioVideoRtpHeaderExtensions(cricket::RtpHeaderExtensions audio_exts,
+                                        cricket::RtpHeaderExtensions video_exts,
+                                        MediaSessionOptions* opts) {
+    auto audio_caps = HeaderExtensionCapabilitiesFromRtpExtensions(audio_exts);
+    auto video_caps = HeaderExtensionCapabilitiesFromRtpExtensions(video_exts);
+    for (auto& entry : opts->media_description_options) {
+      switch (entry.type) {
+        case MEDIA_TYPE_AUDIO:
+          entry.header_extensions = audio_caps;
+          break;
+        case MEDIA_TYPE_VIDEO:
+          entry.header_extensions = video_caps;
+          break;
+        default:
+          break;
+      }
+    }
+  }
+
+ protected:
+  webrtc::test::ScopedKeyValueConfig field_trials;
+  UniqueRandomIdGenerator ssrc_generator1;
+  UniqueRandomIdGenerator ssrc_generator2;
+  TransportDescriptionFactory tdf1_;
+  TransportDescriptionFactory tdf2_;
+  MediaSessionDescriptionFactory f1_;
+  MediaSessionDescriptionFactory f2_;
+};
+
+// Create a typical audio offer, and ensure it matches what we expect.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateAudioOffer) {
+  f1_.set_secure(SEC_ENABLED);
+  std::unique_ptr<SessionDescription> offer =
+      f1_.CreateOffer(CreatePlanBMediaSessionOptions(), NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  const ContentInfo* ac = offer->GetContentByName("audio");
+  const ContentInfo* vc = offer->GetContentByName("video");
+  ASSERT_TRUE(ac != NULL);
+  ASSERT_TRUE(vc == NULL);
+  EXPECT_EQ(MediaProtocolType::kRtp, ac->type);
+  const AudioContentDescription* acd = ac->media_description()->as_audio();
+  EXPECT_EQ(MEDIA_TYPE_AUDIO, acd->type());
+  EXPECT_EQ(f1_.audio_sendrecv_codecs(), acd->codecs());
+  EXPECT_EQ(0U, acd->first_ssrc());             // no sender is attached.
+  EXPECT_EQ(kAutoBandwidth, acd->bandwidth());  // default bandwidth (auto)
+  EXPECT_TRUE(acd->rtcp_mux());                 // rtcp-mux defaults on
+  ASSERT_CRYPTO(acd, 1U, kDefaultSrtpCryptoSuite);
+  EXPECT_EQ(cricket::kMediaProtocolSavpf, acd->protocol());
+}
+
+// Create a typical video offer, and ensure it matches what we expect.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateVideoOffer) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+  f1_.set_secure(SEC_ENABLED);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  const ContentInfo* ac = offer->GetContentByName("audio");
+  const ContentInfo* vc = offer->GetContentByName("video");
+  ASSERT_TRUE(ac != NULL);
+  ASSERT_TRUE(vc != NULL);
+  EXPECT_EQ(MediaProtocolType::kRtp, ac->type);
+  EXPECT_EQ(MediaProtocolType::kRtp, vc->type);
+  const AudioContentDescription* acd = ac->media_description()->as_audio();
+  const VideoContentDescription* vcd = vc->media_description()->as_video();
+  EXPECT_EQ(MEDIA_TYPE_AUDIO, acd->type());
+  EXPECT_EQ(f1_.audio_sendrecv_codecs(), acd->codecs());
+  EXPECT_EQ(0U, acd->first_ssrc());             // no sender is attached
+  EXPECT_EQ(kAutoBandwidth, acd->bandwidth());  // default bandwidth (auto)
+  EXPECT_TRUE(acd->rtcp_mux());                 // rtcp-mux defaults on
+  ASSERT_CRYPTO(acd, 1U, kDefaultSrtpCryptoSuite);
+  EXPECT_EQ(cricket::kMediaProtocolSavpf, acd->protocol());
+  EXPECT_EQ(MEDIA_TYPE_VIDEO, vcd->type());
+  EXPECT_EQ(f1_.video_sendrecv_codecs(), vcd->codecs());
+  EXPECT_EQ(0U, vcd->first_ssrc());             // no sender is attached
+  EXPECT_EQ(kAutoBandwidth, vcd->bandwidth());  // default bandwidth (auto)
+  EXPECT_TRUE(vcd->rtcp_mux());                 // rtcp-mux defaults on
+  ASSERT_CRYPTO(vcd, 1U, kDefaultSrtpCryptoSuite);
+  EXPECT_EQ(cricket::kMediaProtocolSavpf, vcd->protocol());
+}
+
+// Test creating an offer with bundle where the Codecs have the same dynamic
+// RTP playlod type. The test verifies that the offer don't contain the
+// duplicate RTP payload types.
+TEST_F(MediaSessionDescriptionFactoryTest, TestBundleOfferWithSameCodecPlType) {
+  const VideoCodec& offered_video_codec = f2_.video_sendrecv_codecs()[0];
+  const AudioCodec& offered_audio_codec = f2_.audio_sendrecv_codecs()[0];
+  ASSERT_EQ(offered_video_codec.id, offered_audio_codec.id);
+
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+  opts.bundle_enabled = true;
+  std::unique_ptr<SessionDescription> offer = f2_.CreateOffer(opts, NULL);
+  const VideoContentDescription* vcd =
+      GetFirstVideoContentDescription(offer.get());
+  const AudioContentDescription* acd =
+      GetFirstAudioContentDescription(offer.get());
+  ASSERT_TRUE(NULL != vcd);
+  ASSERT_TRUE(NULL != acd);
+  EXPECT_NE(vcd->codecs()[0].id, acd->codecs()[0].id);
+  EXPECT_EQ(vcd->codecs()[0].name, offered_video_codec.name);
+  EXPECT_EQ(acd->codecs()[0].name, offered_audio_codec.name);
+}
+
+// Test creating an updated offer with bundle, audio, video and data
+// after an audio only session has been negotiated.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestCreateUpdatedVideoOfferWithBundle) {
+  f1_.set_secure(SEC_ENABLED);
+  f2_.set_secure(SEC_ENABLED);
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kInactive, kStopped,
+                             &opts);
+  opts.bundle_enabled = true;
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+
+  MediaSessionOptions updated_opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &updated_opts);
+  updated_opts.bundle_enabled = true;
+  std::unique_ptr<SessionDescription> updated_offer(
+      f1_.CreateOffer(updated_opts, answer.get()));
+
+  const AudioContentDescription* acd =
+      GetFirstAudioContentDescription(updated_offer.get());
+  const VideoContentDescription* vcd =
+      GetFirstVideoContentDescription(updated_offer.get());
+  EXPECT_TRUE(NULL != vcd);
+  EXPECT_TRUE(NULL != acd);
+
+  ASSERT_CRYPTO(acd, 1U, kDefaultSrtpCryptoSuite);
+  EXPECT_EQ(cricket::kMediaProtocolSavpf, acd->protocol());
+  ASSERT_CRYPTO(vcd, 1U, kDefaultSrtpCryptoSuite);
+  EXPECT_EQ(cricket::kMediaProtocolSavpf, vcd->protocol());
+}
+
+// Create an SCTP data offer with bundle without error.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateSctpDataOffer) {
+  MediaSessionOptions opts;
+  opts.bundle_enabled = true;
+  AddDataSection(RtpTransceiverDirection::kSendRecv, &opts);
+  f1_.set_secure(SEC_ENABLED);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  EXPECT_TRUE(offer.get() != NULL);
+  EXPECT_TRUE(offer->GetContentByName("data") != NULL);
+  auto dcd = GetFirstSctpDataContentDescription(offer.get());
+  ASSERT_TRUE(dcd);
+  // Since this transport is insecure, the protocol should be "SCTP".
+  EXPECT_EQ(cricket::kMediaProtocolSctp, dcd->protocol());
+}
+
+// Create an SCTP data offer with bundle without error.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateSecureSctpDataOffer) {
+  MediaSessionOptions opts;
+  opts.bundle_enabled = true;
+  AddDataSection(RtpTransceiverDirection::kSendRecv, &opts);
+  f1_.set_secure(SEC_ENABLED);
+  tdf1_.set_secure(SEC_ENABLED);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  EXPECT_TRUE(offer.get() != NULL);
+  EXPECT_TRUE(offer->GetContentByName("data") != NULL);
+  auto dcd = GetFirstSctpDataContentDescription(offer.get());
+  ASSERT_TRUE(dcd);
+  // The protocol should now be "UDP/DTLS/SCTP"
+  EXPECT_EQ(cricket::kMediaProtocolUdpDtlsSctp, dcd->protocol());
+}
+
+// Test creating an sctp data channel from an already generated offer.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateImplicitSctpDataOffer) {
+  MediaSessionOptions opts;
+  opts.bundle_enabled = true;
+  AddDataSection(RtpTransceiverDirection::kSendRecv, &opts);
+  f1_.set_secure(SEC_ENABLED);
+  std::unique_ptr<SessionDescription> offer1(f1_.CreateOffer(opts, NULL));
+  ASSERT_TRUE(offer1.get() != NULL);
+  const ContentInfo* data = offer1->GetContentByName("data");
+  ASSERT_TRUE(data != NULL);
+  ASSERT_EQ(cricket::kMediaProtocolSctp, data->media_description()->protocol());
+
+  std::unique_ptr<SessionDescription> offer2(
+      f1_.CreateOffer(opts, offer1.get()));
+  data = offer2->GetContentByName("data");
+  ASSERT_TRUE(data != NULL);
+  EXPECT_EQ(cricket::kMediaProtocolSctp, data->media_description()->protocol());
+}
+
+// Test that if BUNDLE is enabled and all media sections are rejected then the
+// BUNDLE group is not present in the re-offer.
+TEST_F(MediaSessionDescriptionFactoryTest, ReOfferNoBundleGroupIfAllRejected) {
+  MediaSessionOptions opts;
+  opts.bundle_enabled = true;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+
+  opts.media_description_options[0].stopped = true;
+  std::unique_ptr<SessionDescription> reoffer =
+      f1_.CreateOffer(opts, offer.get());
+
+  EXPECT_FALSE(reoffer->GetGroupByName(cricket::GROUP_TYPE_BUNDLE));
+}
+
+// Test that if BUNDLE is enabled and the remote re-offer does not include a
+// BUNDLE group since all media sections are rejected, then the re-answer also
+// does not include a BUNDLE group.
+TEST_F(MediaSessionDescriptionFactoryTest, ReAnswerNoBundleGroupIfAllRejected) {
+  MediaSessionOptions opts;
+  opts.bundle_enabled = true;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+
+  opts.media_description_options[0].stopped = true;
+  std::unique_ptr<SessionDescription> reoffer =
+      f1_.CreateOffer(opts, offer.get());
+  std::unique_ptr<SessionDescription> reanswer =
+      f2_.CreateAnswer(reoffer.get(), opts, answer.get());
+
+  EXPECT_FALSE(reanswer->GetGroupByName(cricket::GROUP_TYPE_BUNDLE));
+}
+
+// Test that if BUNDLE is enabled and the previous offerer-tagged media section
+// was rejected then the new offerer-tagged media section is the non-rejected
+// media section.
+TEST_F(MediaSessionDescriptionFactoryTest, ReOfferChangeBundleOffererTagged) {
+  MediaSessionOptions opts;
+  opts.bundle_enabled = true;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+
+  // Reject the audio m= section and add a video m= section.
+  opts.media_description_options[0].stopped = true;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  std::unique_ptr<SessionDescription> reoffer =
+      f1_.CreateOffer(opts, offer.get());
+
+  const cricket::ContentGroup* bundle_group =
+      reoffer->GetGroupByName(cricket::GROUP_TYPE_BUNDLE);
+  ASSERT_TRUE(bundle_group);
+  EXPECT_FALSE(bundle_group->HasContentName("audio"));
+  EXPECT_TRUE(bundle_group->HasContentName("video"));
+}
+
+// Test that if BUNDLE is enabled and the previous offerer-tagged media section
+// was rejected and a new media section is added, then the re-answer BUNDLE
+// group will contain only the non-rejected media section.
+TEST_F(MediaSessionDescriptionFactoryTest, ReAnswerChangedBundleOffererTagged) {
+  MediaSessionOptions opts;
+  opts.bundle_enabled = true;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+
+  // Reject the audio m= section and add a video m= section.
+  opts.media_description_options[0].stopped = true;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  std::unique_ptr<SessionDescription> reoffer =
+      f1_.CreateOffer(opts, offer.get());
+  std::unique_ptr<SessionDescription> reanswer =
+      f2_.CreateAnswer(reoffer.get(), opts, answer.get());
+
+  const cricket::ContentGroup* bundle_group =
+      reanswer->GetGroupByName(cricket::GROUP_TYPE_BUNDLE);
+  ASSERT_TRUE(bundle_group);
+  EXPECT_FALSE(bundle_group->HasContentName("audio"));
+  EXPECT_TRUE(bundle_group->HasContentName("video"));
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       CreateAnswerForOfferWithMultipleBundleGroups) {
+  // Create an offer with 4 m= sections, initially without BUNDLE groups.
+  MediaSessionOptions opts;
+  opts.bundle_enabled = false;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "1",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "2",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "3",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "4",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  ASSERT_TRUE(offer->groups().empty());
+
+  // Munge the offer to have two groups. Offers like these cannot be generated
+  // without munging, but it is valid to receive such offers from remote
+  // endpoints.
+  cricket::ContentGroup bundle_group1(cricket::GROUP_TYPE_BUNDLE);
+  bundle_group1.AddContentName("1");
+  bundle_group1.AddContentName("2");
+  cricket::ContentGroup bundle_group2(cricket::GROUP_TYPE_BUNDLE);
+  bundle_group2.AddContentName("3");
+  bundle_group2.AddContentName("4");
+  offer->AddGroup(bundle_group1);
+  offer->AddGroup(bundle_group2);
+
+  // If BUNDLE is enabled, the answer to this offer should accept both BUNDLE
+  // groups.
+  opts.bundle_enabled = true;
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+
+  std::vector<const cricket::ContentGroup*> answer_groups =
+      answer->GetGroupsByName(cricket::GROUP_TYPE_BUNDLE);
+  ASSERT_EQ(answer_groups.size(), 2u);
+  EXPECT_EQ(answer_groups[0]->content_names().size(), 2u);
+  EXPECT_TRUE(answer_groups[0]->HasContentName("1"));
+  EXPECT_TRUE(answer_groups[0]->HasContentName("2"));
+  EXPECT_EQ(answer_groups[1]->content_names().size(), 2u);
+  EXPECT_TRUE(answer_groups[1]->HasContentName("3"));
+  EXPECT_TRUE(answer_groups[1]->HasContentName("4"));
+
+  // If BUNDLE is disabled, the answer to this offer should reject both BUNDLE
+  // groups.
+  opts.bundle_enabled = false;
+  answer = f2_.CreateAnswer(offer.get(), opts, nullptr);
+
+  answer_groups = answer->GetGroupsByName(cricket::GROUP_TYPE_BUNDLE);
+  // Rejected groups are still listed, but they are empty.
+  ASSERT_EQ(answer_groups.size(), 2u);
+  EXPECT_TRUE(answer_groups[0]->content_names().empty());
+  EXPECT_TRUE(answer_groups[1]->content_names().empty());
+}
+
+// Test that if the BUNDLE offerer-tagged media section is changed in a reoffer
+// and there is still a non-rejected media section that was in the initial
+// offer, then the ICE credentials do not change in the reoffer offerer-tagged
+// media section.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       ReOfferChangeBundleOffererTaggedKeepsIceCredentials) {
+  MediaSessionOptions opts;
+  opts.bundle_enabled = true;
+  AddAudioVideoSections(RtpTransceiverDirection::kSendRecv, &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+
+  // Reject the audio m= section.
+  opts.media_description_options[0].stopped = true;
+  std::unique_ptr<SessionDescription> reoffer =
+      f1_.CreateOffer(opts, offer.get());
+
+  const TransportDescription* offer_tagged =
+      offer->GetTransportDescriptionByName("audio");
+  ASSERT_TRUE(offer_tagged);
+  const TransportDescription* reoffer_tagged =
+      reoffer->GetTransportDescriptionByName("video");
+  ASSERT_TRUE(reoffer_tagged);
+  EXPECT_EQ(offer_tagged->ice_ufrag, reoffer_tagged->ice_ufrag);
+  EXPECT_EQ(offer_tagged->ice_pwd, reoffer_tagged->ice_pwd);
+}
+
+// Test that if the BUNDLE offerer-tagged media section is changed in a reoffer
+// and there is still a non-rejected media section that was in the initial
+// offer, then the ICE credentials do not change in the reanswer answerer-tagged
+// media section.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       ReAnswerChangeBundleOffererTaggedKeepsIceCredentials) {
+  MediaSessionOptions opts;
+  opts.bundle_enabled = true;
+  AddAudioVideoSections(RtpTransceiverDirection::kSendRecv, &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+
+  // Reject the audio m= section.
+  opts.media_description_options[0].stopped = true;
+  std::unique_ptr<SessionDescription> reoffer =
+      f1_.CreateOffer(opts, offer.get());
+  std::unique_ptr<SessionDescription> reanswer =
+      f2_.CreateAnswer(reoffer.get(), opts, answer.get());
+
+  const TransportDescription* answer_tagged =
+      answer->GetTransportDescriptionByName("audio");
+  ASSERT_TRUE(answer_tagged);
+  const TransportDescription* reanswer_tagged =
+      reanswer->GetTransportDescriptionByName("video");
+  ASSERT_TRUE(reanswer_tagged);
+  EXPECT_EQ(answer_tagged->ice_ufrag, reanswer_tagged->ice_ufrag);
+  EXPECT_EQ(answer_tagged->ice_pwd, reanswer_tagged->ice_pwd);
+}
+
+// Create an audio, video offer without legacy StreamParams.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestCreateOfferWithoutLegacyStreams) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  const ContentInfo* ac = offer->GetContentByName("audio");
+  const ContentInfo* vc = offer->GetContentByName("video");
+  ASSERT_TRUE(ac != NULL);
+  ASSERT_TRUE(vc != NULL);
+  const AudioContentDescription* acd = ac->media_description()->as_audio();
+  const VideoContentDescription* vcd = vc->media_description()->as_video();
+
+  EXPECT_FALSE(vcd->has_ssrcs());  // No StreamParams.
+  EXPECT_FALSE(acd->has_ssrcs());  // No StreamParams.
+}
+
+// Creates an audio+video sendonly offer.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateSendOnlyOffer) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kSendOnly, &opts);
+  AttachSenderToMediaDescriptionOptions("video", MEDIA_TYPE_VIDEO, kVideoTrack1,
+                                        {kMediaStream1}, 1, &opts);
+  AttachSenderToMediaDescriptionOptions("audio", MEDIA_TYPE_AUDIO, kAudioTrack1,
+                                        {kMediaStream1}, 1, &opts);
+
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  EXPECT_EQ(2u, offer->contents().size());
+  EXPECT_TRUE(IsMediaContentOfType(&offer->contents()[0], MEDIA_TYPE_AUDIO));
+  EXPECT_TRUE(IsMediaContentOfType(&offer->contents()[1], MEDIA_TYPE_VIDEO));
+
+  EXPECT_EQ(RtpTransceiverDirection::kSendOnly,
+            GetMediaDirection(&offer->contents()[0]));
+  EXPECT_EQ(RtpTransceiverDirection::kSendOnly,
+            GetMediaDirection(&offer->contents()[1]));
+}
+
+// Verifies that the order of the media contents in the current
+// SessionDescription is preserved in the new SessionDescription.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateOfferContentOrder) {
+  MediaSessionOptions opts;
+  AddDataSection(RtpTransceiverDirection::kSendRecv, &opts);
+
+  std::unique_ptr<SessionDescription> offer1(f1_.CreateOffer(opts, NULL));
+  ASSERT_TRUE(offer1.get() != NULL);
+  EXPECT_EQ(1u, offer1->contents().size());
+  EXPECT_TRUE(IsMediaContentOfType(&offer1->contents()[0], MEDIA_TYPE_DATA));
+
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &opts);
+  std::unique_ptr<SessionDescription> offer2(
+      f1_.CreateOffer(opts, offer1.get()));
+  ASSERT_TRUE(offer2.get() != NULL);
+  EXPECT_EQ(2u, offer2->contents().size());
+  EXPECT_TRUE(IsMediaContentOfType(&offer2->contents()[0], MEDIA_TYPE_DATA));
+  EXPECT_TRUE(IsMediaContentOfType(&offer2->contents()[1], MEDIA_TYPE_VIDEO));
+
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &opts);
+  std::unique_ptr<SessionDescription> offer3(
+      f1_.CreateOffer(opts, offer2.get()));
+  ASSERT_TRUE(offer3.get() != NULL);
+  EXPECT_EQ(3u, offer3->contents().size());
+  EXPECT_TRUE(IsMediaContentOfType(&offer3->contents()[0], MEDIA_TYPE_DATA));
+  EXPECT_TRUE(IsMediaContentOfType(&offer3->contents()[1], MEDIA_TYPE_VIDEO));
+  EXPECT_TRUE(IsMediaContentOfType(&offer3->contents()[2], MEDIA_TYPE_AUDIO));
+}
+
+// Create a typical audio answer, and ensure it matches what we expect.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateAudioAnswer) {
+  f1_.set_secure(SEC_ENABLED);
+  f2_.set_secure(SEC_ENABLED);
+  std::unique_ptr<SessionDescription> offer =
+      f1_.CreateOffer(CreatePlanBMediaSessionOptions(), NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), CreatePlanBMediaSessionOptions(), NULL);
+  const ContentInfo* ac = answer->GetContentByName("audio");
+  const ContentInfo* vc = answer->GetContentByName("video");
+  ASSERT_TRUE(ac != NULL);
+  ASSERT_TRUE(vc == NULL);
+  EXPECT_EQ(MediaProtocolType::kRtp, ac->type);
+  const AudioContentDescription* acd = ac->media_description()->as_audio();
+  EXPECT_EQ(MEDIA_TYPE_AUDIO, acd->type());
+  EXPECT_THAT(acd->codecs(), ElementsAreArray(kAudioCodecsAnswer));
+  EXPECT_EQ(0U, acd->first_ssrc());             // no sender is attached
+  EXPECT_EQ(kAutoBandwidth, acd->bandwidth());  // negotiated auto bw
+  EXPECT_TRUE(acd->rtcp_mux());                 // negotiated rtcp-mux
+  ASSERT_CRYPTO(acd, 1U, kDefaultSrtpCryptoSuite);
+  EXPECT_EQ(cricket::kMediaProtocolSavpf, acd->protocol());
+}
+
+// Create a typical audio answer with GCM ciphers enabled, and ensure it
+// matches what we expect.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateAudioAnswerGcm) {
+  f1_.set_secure(SEC_ENABLED);
+  f2_.set_secure(SEC_ENABLED);
+  MediaSessionOptions opts = CreatePlanBMediaSessionOptions();
+  opts.crypto_options.srtp.enable_gcm_crypto_suites = true;
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  for (cricket::ContentInfo& content : offer->contents()) {
+    auto cryptos = content.media_description()->cryptos();
+    PreferGcmCryptoParameters(&cryptos);
+    content.media_description()->set_cryptos(cryptos);
+  }
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+  const ContentInfo* ac = answer->GetContentByName("audio");
+  const ContentInfo* vc = answer->GetContentByName("video");
+  ASSERT_TRUE(ac != NULL);
+  ASSERT_TRUE(vc == NULL);
+  EXPECT_EQ(MediaProtocolType::kRtp, ac->type);
+  const AudioContentDescription* acd = ac->media_description()->as_audio();
+  EXPECT_EQ(MEDIA_TYPE_AUDIO, acd->type());
+  EXPECT_THAT(acd->codecs(), ElementsAreArray(kAudioCodecsAnswer));
+  EXPECT_EQ(0U, acd->first_ssrc());             // no sender is attached
+  EXPECT_EQ(kAutoBandwidth, acd->bandwidth());  // negotiated auto bw
+  EXPECT_TRUE(acd->rtcp_mux());                 // negotiated rtcp-mux
+  ASSERT_CRYPTO(acd, 1U, kDefaultSrtpCryptoSuiteGcm);
+  EXPECT_EQ(cricket::kMediaProtocolSavpf, acd->protocol());
+}
+
+// Create an audio answer with no common codecs, and ensure it is rejected.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestCreateAudioAnswerWithNoCommonCodecs) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  std::vector f1_codecs = {AudioCodec(96, "opus", 48000, -1, 1)};
+  f1_.set_audio_codecs(f1_codecs, f1_codecs);
+
+  std::vector f2_codecs = {AudioCodec(0, "PCMU", 8000, -1, 1)};
+  f2_.set_audio_codecs(f2_codecs, f2_codecs);
+
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+  const ContentInfo* ac = answer->GetContentByName("audio");
+  ASSERT_TRUE(ac != NULL);
+  EXPECT_TRUE(ac->rejected);
+}
+
+// Create a typical video answer, and ensure it matches what we expect.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateVideoAnswer) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+  f1_.set_secure(SEC_ENABLED);
+  f2_.set_secure(SEC_ENABLED);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+  const ContentInfo* ac = answer->GetContentByName("audio");
+  const ContentInfo* vc = answer->GetContentByName("video");
+  ASSERT_TRUE(ac != NULL);
+  ASSERT_TRUE(vc != NULL);
+  EXPECT_EQ(MediaProtocolType::kRtp, ac->type);
+  EXPECT_EQ(MediaProtocolType::kRtp, vc->type);
+  const AudioContentDescription* acd = ac->media_description()->as_audio();
+  const VideoContentDescription* vcd = vc->media_description()->as_video();
+  EXPECT_EQ(MEDIA_TYPE_AUDIO, acd->type());
+  EXPECT_THAT(acd->codecs(), ElementsAreArray(kAudioCodecsAnswer));
+  EXPECT_EQ(kAutoBandwidth, acd->bandwidth());  // negotiated auto bw
+  EXPECT_EQ(0U, acd->first_ssrc());             // no sender is attached
+  EXPECT_TRUE(acd->rtcp_mux());                 // negotiated rtcp-mux
+  ASSERT_CRYPTO(acd, 1U, kDefaultSrtpCryptoSuite);
+  EXPECT_EQ(MEDIA_TYPE_VIDEO, vcd->type());
+  EXPECT_THAT(vcd->codecs(), ElementsAreArray(kVideoCodecsAnswer));
+  EXPECT_EQ(0U, vcd->first_ssrc());  // no sender is attached
+  EXPECT_TRUE(vcd->rtcp_mux());      // negotiated rtcp-mux
+  ASSERT_CRYPTO(vcd, 1U, kDefaultSrtpCryptoSuite);
+  EXPECT_EQ(cricket::kMediaProtocolSavpf, vcd->protocol());
+}
+
+// Create a typical video answer with GCM ciphers enabled, and ensure it
+// matches what we expect.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateVideoAnswerGcm) {
+  TestVideoGcmCipher(true, true);
+}
+
+// Create a typical video answer with GCM ciphers enabled for the offer only,
+// and ensure it matches what we expect.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateVideoAnswerGcmOffer) {
+  TestVideoGcmCipher(true, false);
+}
+
+// Create a typical video answer with GCM ciphers enabled for the answer only,
+// and ensure it matches what we expect.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateVideoAnswerGcmAnswer) {
+  TestVideoGcmCipher(false, true);
+}
+
+// Create a video answer with no common codecs, and ensure it is rejected.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestCreateVideoAnswerWithNoCommonCodecs) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  std::vector f1_codecs = {VideoCodec(96, "H264")};
+  f1_.set_video_codecs(f1_codecs, f1_codecs);
+
+  std::vector f2_codecs = {VideoCodec(97, "VP8")};
+  f2_.set_video_codecs(f2_codecs, f2_codecs);
+
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+  const ContentInfo* vc = answer->GetContentByName("video");
+  ASSERT_TRUE(vc != NULL);
+  EXPECT_TRUE(vc->rejected);
+}
+
+// Create a video answer with no common codecs (but a common FEC codec), and
+// ensure it is rejected.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestCreateVideoAnswerWithOnlyFecCodecsCommon) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  std::vector f1_codecs = {VideoCodec(96, "H264"),
+                           VideoCodec(118, "flexfec-03")};
+  f1_.set_video_codecs(f1_codecs, f1_codecs);
+
+  std::vector f2_codecs = {VideoCodec(97, "VP8"),
+                           VideoCodec(118, "flexfec-03")};
+  f2_.set_video_codecs(f2_codecs, f2_codecs);
+
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+  const ContentInfo* vc = answer->GetContentByName("video");
+  ASSERT_TRUE(vc != NULL);
+  EXPECT_TRUE(vc->rejected);
+}
+
+// The use_sctpmap flag should be set in an Sctp DataContentDescription by
+// default. The answer's use_sctpmap flag should match the offer's.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateDataAnswerUsesSctpmap) {
+  MediaSessionOptions opts;
+  AddDataSection(RtpTransceiverDirection::kSendRecv, &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  ContentInfo* dc_offer = offer->GetContentByName("data");
+  ASSERT_TRUE(dc_offer != NULL);
+  SctpDataContentDescription* dcd_offer =
+      dc_offer->media_description()->as_sctp();
+  EXPECT_TRUE(dcd_offer->use_sctpmap());
+
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+  const ContentInfo* dc_answer = answer->GetContentByName("data");
+  ASSERT_TRUE(dc_answer != NULL);
+  const SctpDataContentDescription* dcd_answer =
+      dc_answer->media_description()->as_sctp();
+  EXPECT_TRUE(dcd_answer->use_sctpmap());
+}
+
+// The answer's use_sctpmap flag should match the offer's.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateDataAnswerWithoutSctpmap) {
+  MediaSessionOptions opts;
+  AddDataSection(RtpTransceiverDirection::kSendRecv, &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  ContentInfo* dc_offer = offer->GetContentByName("data");
+  ASSERT_TRUE(dc_offer != NULL);
+  SctpDataContentDescription* dcd_offer =
+      dc_offer->media_description()->as_sctp();
+  dcd_offer->set_use_sctpmap(false);
+
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+  const ContentInfo* dc_answer = answer->GetContentByName("data");
+  ASSERT_TRUE(dc_answer != NULL);
+  const SctpDataContentDescription* dcd_answer =
+      dc_answer->media_description()->as_sctp();
+  EXPECT_FALSE(dcd_answer->use_sctpmap());
+}
+
+// Test that a valid answer will be created for "DTLS/SCTP", "UDP/DTLS/SCTP"
+// and "TCP/DTLS/SCTP" offers.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestCreateDataAnswerToDifferentOfferedProtos) {
+  // Need to enable DTLS offer/answer generation (disabled by default in this
+  // test).
+  f1_.set_secure(SEC_ENABLED);
+  f2_.set_secure(SEC_ENABLED);
+  tdf1_.set_secure(SEC_ENABLED);
+  tdf2_.set_secure(SEC_ENABLED);
+
+  MediaSessionOptions opts;
+  AddDataSection(RtpTransceiverDirection::kSendRecv, &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  ASSERT_TRUE(offer.get() != nullptr);
+  ContentInfo* dc_offer = offer->GetContentByName("data");
+  ASSERT_TRUE(dc_offer != nullptr);
+  SctpDataContentDescription* dcd_offer =
+      dc_offer->media_description()->as_sctp();
+  ASSERT_TRUE(dcd_offer);
+
+  std::vector<std::string> protos = {"DTLS/SCTP", "UDP/DTLS/SCTP",
+                                     "TCP/DTLS/SCTP"};
+  for (const std::string& proto : protos) {
+    dcd_offer->set_protocol(proto);
+    std::unique_ptr<SessionDescription> answer =
+        f2_.CreateAnswer(offer.get(), opts, nullptr);
+    const ContentInfo* dc_answer = answer->GetContentByName("data");
+    ASSERT_TRUE(dc_answer != nullptr);
+    const SctpDataContentDescription* dcd_answer =
+        dc_answer->media_description()->as_sctp();
+    EXPECT_FALSE(dc_answer->rejected);
+    EXPECT_EQ(proto, dcd_answer->protocol());
+  }
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestCreateDataAnswerToOfferWithDefinedMessageSize) {
+  // Need to enable DTLS offer/answer generation (disabled by default in this
+  // test).
+  f1_.set_secure(SEC_ENABLED);
+  f2_.set_secure(SEC_ENABLED);
+  tdf1_.set_secure(SEC_ENABLED);
+  tdf2_.set_secure(SEC_ENABLED);
+
+  MediaSessionOptions opts;
+  AddDataSection(RtpTransceiverDirection::kSendRecv, &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  ASSERT_TRUE(offer.get() != nullptr);
+  ContentInfo* dc_offer = offer->GetContentByName("data");
+  ASSERT_TRUE(dc_offer != nullptr);
+  SctpDataContentDescription* dcd_offer =
+      dc_offer->media_description()->as_sctp();
+  ASSERT_TRUE(dcd_offer);
+  dcd_offer->set_max_message_size(1234);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+  const ContentInfo* dc_answer = answer->GetContentByName("data");
+  ASSERT_TRUE(dc_answer != nullptr);
+  const SctpDataContentDescription* dcd_answer =
+      dc_answer->media_description()->as_sctp();
+  EXPECT_FALSE(dc_answer->rejected);
+  EXPECT_EQ(1234, dcd_answer->max_message_size());
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestCreateDataAnswerToOfferWithZeroMessageSize) {
+  // Need to enable DTLS offer/answer generation (disabled by default in this
+  // test).
+  f1_.set_secure(SEC_ENABLED);
+  f2_.set_secure(SEC_ENABLED);
+  tdf1_.set_secure(SEC_ENABLED);
+  tdf2_.set_secure(SEC_ENABLED);
+
+  MediaSessionOptions opts;
+  AddDataSection(RtpTransceiverDirection::kSendRecv, &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  ASSERT_TRUE(offer.get() != nullptr);
+  ContentInfo* dc_offer = offer->GetContentByName("data");
+  ASSERT_TRUE(dc_offer != nullptr);
+  SctpDataContentDescription* dcd_offer =
+      dc_offer->media_description()->as_sctp();
+  ASSERT_TRUE(dcd_offer);
+  dcd_offer->set_max_message_size(0);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+  const ContentInfo* dc_answer = answer->GetContentByName("data");
+  ASSERT_TRUE(dc_answer != nullptr);
+  const SctpDataContentDescription* dcd_answer =
+      dc_answer->media_description()->as_sctp();
+  EXPECT_FALSE(dc_answer->rejected);
+  EXPECT_EQ(cricket::kSctpSendBufferSize, dcd_answer->max_message_size());
+}
+
+// Verifies that the order of the media contents in the offer is preserved in
+// the answer.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateAnswerContentOrder) {
+  MediaSessionOptions opts;
+
+  // Creates a data only offer.
+  AddDataSection(RtpTransceiverDirection::kSendRecv, &opts);
+  std::unique_ptr<SessionDescription> offer1(f1_.CreateOffer(opts, NULL));
+  ASSERT_TRUE(offer1.get() != NULL);
+
+  // Appends audio to the offer.
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &opts);
+  std::unique_ptr<SessionDescription> offer2(
+      f1_.CreateOffer(opts, offer1.get()));
+  ASSERT_TRUE(offer2.get() != NULL);
+
+  // Appends video to the offer.
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &opts);
+  std::unique_ptr<SessionDescription> offer3(
+      f1_.CreateOffer(opts, offer2.get()));
+  ASSERT_TRUE(offer3.get() != NULL);
+
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer3.get(), opts, NULL);
+  ASSERT_TRUE(answer.get() != NULL);
+  EXPECT_EQ(3u, answer->contents().size());
+  EXPECT_TRUE(IsMediaContentOfType(&answer->contents()[0], MEDIA_TYPE_DATA));
+  EXPECT_TRUE(IsMediaContentOfType(&answer->contents()[1], MEDIA_TYPE_AUDIO));
+  EXPECT_TRUE(IsMediaContentOfType(&answer->contents()[2], MEDIA_TYPE_VIDEO));
+}
+
+// TODO(deadbeef): Extend these tests to ensure the correct direction with other
+// answerer settings.
+
+// This test that the media direction is set to send/receive in an answer if
+// the offer is send receive.
+TEST_F(MediaSessionDescriptionFactoryTest, CreateAnswerToSendReceiveOffer) {
+  TestMediaDirectionInAnswer(RtpTransceiverDirection::kSendRecv,
+                             RtpTransceiverDirection::kSendRecv);
+}
+
+// This test that the media direction is set to receive only in an answer if
+// the offer is send only.
+TEST_F(MediaSessionDescriptionFactoryTest, CreateAnswerToSendOnlyOffer) {
+  TestMediaDirectionInAnswer(RtpTransceiverDirection::kSendOnly,
+                             RtpTransceiverDirection::kRecvOnly);
+}
+
+// This test that the media direction is set to send only in an answer if
+// the offer is recv only.
+TEST_F(MediaSessionDescriptionFactoryTest, CreateAnswerToRecvOnlyOffer) {
+  TestMediaDirectionInAnswer(RtpTransceiverDirection::kRecvOnly,
+                             RtpTransceiverDirection::kSendOnly);
+}
+
+// This test that the media direction is set to inactive in an answer if
+// the offer is inactive.
+TEST_F(MediaSessionDescriptionFactoryTest, CreateAnswerToInactiveOffer) {
+  TestMediaDirectionInAnswer(RtpTransceiverDirection::kInactive,
+                             RtpTransceiverDirection::kInactive);
+}
+
+// Test that the media protocol is RTP/AVPF if DTLS and SDES are disabled.
+TEST_F(MediaSessionDescriptionFactoryTest, AudioOfferAnswerWithCryptoDisabled) {
+  MediaSessionOptions opts = CreatePlanBMediaSessionOptions();
+  f1_.set_secure(SEC_DISABLED);
+  f2_.set_secure(SEC_DISABLED);
+  tdf1_.set_secure(SEC_DISABLED);
+  tdf2_.set_secure(SEC_DISABLED);
+
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  const AudioContentDescription* offer_acd =
+      GetFirstAudioContentDescription(offer.get());
+  ASSERT_TRUE(offer_acd != NULL);
+  EXPECT_EQ(cricket::kMediaProtocolAvpf, offer_acd->protocol());
+
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+
+  const ContentInfo* ac_answer = answer->GetContentByName("audio");
+  ASSERT_TRUE(ac_answer != NULL);
+  EXPECT_FALSE(ac_answer->rejected);
+
+  const AudioContentDescription* answer_acd =
+      GetFirstAudioContentDescription(answer.get());
+  ASSERT_TRUE(answer_acd != NULL);
+  EXPECT_EQ(cricket::kMediaProtocolAvpf, answer_acd->protocol());
+}
+
+// Create a video offer and answer and ensure the RTP header extensions
+// matches what we expect.
+TEST_F(MediaSessionDescriptionFactoryTest, TestOfferAnswerWithRtpExtensions) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+  SetAudioVideoRtpHeaderExtensions(MAKE_VECTOR(kAudioRtpExtension1),
+                                   MAKE_VECTOR(kVideoRtpExtension1), &opts);
+
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  SetAudioVideoRtpHeaderExtensions(MAKE_VECTOR(kAudioRtpExtension2),
+                                   MAKE_VECTOR(kVideoRtpExtension2), &opts);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+
+  EXPECT_EQ(
+      MAKE_VECTOR(kAudioRtpExtension1),
+      GetFirstAudioContentDescription(offer.get())->rtp_header_extensions());
+  EXPECT_EQ(
+      MAKE_VECTOR(kVideoRtpExtension1),
+      GetFirstVideoContentDescription(offer.get())->rtp_header_extensions());
+  EXPECT_EQ(
+      MAKE_VECTOR(kAudioRtpExtensionAnswer),
+      GetFirstAudioContentDescription(answer.get())->rtp_header_extensions());
+  EXPECT_EQ(
+      MAKE_VECTOR(kVideoRtpExtensionAnswer),
+      GetFirstVideoContentDescription(answer.get())->rtp_header_extensions());
+}
+
+// Create a audio/video offer and answer and ensure that the
+// TransportSequenceNumber RTP header extensions are handled correctly. 02 is
+// supported and should take precedence even though not listed among locally
+// supported extensions.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestOfferAnswerWithTransportSequenceNumberInOffer) {
+  TestTransportSequenceNumberNegotiation(
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber01),   // Local.
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber01),   // Offer.
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber01));  // Expected answer.
+}
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestOfferAnswerWithTransportSequenceNumber01And02InOffer) {
+  TestTransportSequenceNumberNegotiation(
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber01),       // Local.
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber01And02),  // Offer.
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber02));  // Expected answer.
+}
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestOfferAnswerWithTransportSequenceNumber02InOffer) {
+  TestTransportSequenceNumberNegotiation(
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber01),   // Local.
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber02),   // Offer.
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber02));  // Expected answer.
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestNegotiateFrameDescriptorWhenUnexposedLocally) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+
+  SetAudioVideoRtpHeaderExtensions(
+      MAKE_VECTOR(kRtpExtensionGenericFrameDescriptorUri00),
+      MAKE_VECTOR(kRtpExtensionGenericFrameDescriptorUri00), &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  SetAudioVideoRtpHeaderExtensions(
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber01),
+      MAKE_VECTOR(kRtpExtensionTransportSequenceNumber01), &opts);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+  EXPECT_THAT(
+      GetFirstAudioContentDescription(answer.get())->rtp_header_extensions(),
+      ElementsAreArray(kRtpExtensionGenericFrameDescriptorUri00));
+  EXPECT_THAT(
+      GetFirstVideoContentDescription(answer.get())->rtp_header_extensions(),
+      ElementsAreArray(kRtpExtensionGenericFrameDescriptorUri00));
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestNegotiateFrameDescriptorWhenExposedLocally) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+
+  SetAudioVideoRtpHeaderExtensions(
+      MAKE_VECTOR(kRtpExtensionGenericFrameDescriptorUri00),
+      MAKE_VECTOR(kRtpExtensionGenericFrameDescriptorUri00), &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+  EXPECT_THAT(
+      GetFirstAudioContentDescription(answer.get())->rtp_header_extensions(),
+      ElementsAreArray(kRtpExtensionGenericFrameDescriptorUri00));
+  EXPECT_THAT(
+      GetFirstVideoContentDescription(answer.get())->rtp_header_extensions(),
+      ElementsAreArray(kRtpExtensionGenericFrameDescriptorUri00));
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       NegotiateDependencyDescriptorWhenUnexposedLocally) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+
+  RtpExtension offer_dd(RtpExtension::kDependencyDescriptorUri, 7);
+  SetAudioVideoRtpHeaderExtensions({}, {offer_dd}, &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  RtpExtension local_tsn(RtpExtension::kTransportSequenceNumberUri, 5);
+  SetAudioVideoRtpHeaderExtensions({}, {local_tsn}, &opts);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+  EXPECT_THAT(
+      GetFirstVideoContentDescription(answer.get())->rtp_header_extensions(),
+      ElementsAre(offer_dd));
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       NegotiateDependencyDescriptorWhenExposedLocally) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+
+  RtpExtension offer_dd(RtpExtension::kDependencyDescriptorUri, 7);
+  RtpExtension local_dd(RtpExtension::kDependencyDescriptorUri, 5);
+  SetAudioVideoRtpHeaderExtensions({}, {offer_dd}, &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  SetAudioVideoRtpHeaderExtensions({}, {local_dd}, &opts);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+  EXPECT_THAT(
+      GetFirstVideoContentDescription(answer.get())->rtp_header_extensions(),
+      ElementsAre(offer_dd));
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       NegotiateAbsoluteCaptureTimeWhenUnexposedLocally) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+
+  const cricket::RtpHeaderExtensions offered_extensions = {
+      RtpExtension(RtpExtension::kAbsoluteCaptureTimeUri, 7)};
+  const cricket::RtpHeaderExtensions local_extensions = {
+      RtpExtension(RtpExtension::kTransportSequenceNumberUri, 5)};
+  SetAudioVideoRtpHeaderExtensions(offered_extensions, offered_extensions,
+                                   &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  SetAudioVideoRtpHeaderExtensions(local_extensions, local_extensions, &opts);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+  EXPECT_THAT(
+      GetFirstVideoContentDescription(answer.get())->rtp_header_extensions(),
+      ElementsAreArray(offered_extensions));
+  EXPECT_THAT(
+      GetFirstAudioContentDescription(answer.get())->rtp_header_extensions(),
+      ElementsAreArray(offered_extensions));
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       NegotiateAbsoluteCaptureTimeWhenExposedLocally) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+
+  const cricket::RtpHeaderExtensions offered_extensions = {
+      RtpExtension(RtpExtension::kAbsoluteCaptureTimeUri, 7)};
+  const cricket::RtpHeaderExtensions local_extensions = {
+      RtpExtension(RtpExtension::kAbsoluteCaptureTimeUri, 5)};
+  SetAudioVideoRtpHeaderExtensions(offered_extensions, offered_extensions,
+                                   &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  SetAudioVideoRtpHeaderExtensions(local_extensions, local_extensions, &opts);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+  EXPECT_THAT(
+      GetFirstVideoContentDescription(answer.get())->rtp_header_extensions(),
+      ElementsAreArray(offered_extensions));
+  EXPECT_THAT(
+      GetFirstAudioContentDescription(answer.get())->rtp_header_extensions(),
+      ElementsAreArray(offered_extensions));
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       DoNotNegotiateAbsoluteCaptureTimeWhenNotOffered) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+
+  const cricket::RtpHeaderExtensions offered_extensions = {
+      RtpExtension(RtpExtension::kTransportSequenceNumberUri, 7)};
+  const cricket::RtpHeaderExtensions local_extensions = {
+      RtpExtension(RtpExtension::kAbsoluteCaptureTimeUri, 5)};
+  SetAudioVideoRtpHeaderExtensions(offered_extensions, offered_extensions,
+                                   &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  SetAudioVideoRtpHeaderExtensions(local_extensions, local_extensions, &opts);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+  EXPECT_THAT(
+      GetFirstVideoContentDescription(answer.get())->rtp_header_extensions(),
+      IsEmpty());
+  EXPECT_THAT(
+      GetFirstAudioContentDescription(answer.get())->rtp_header_extensions(),
+      IsEmpty());
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       OffersUnstoppedExtensionsWithAudioVideoExtensionStopped) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  opts.media_description_options.back().header_extensions = {
+      webrtc::RtpHeaderExtensionCapability("uri1", 1,
+                                           RtpTransceiverDirection::kStopped),
+      webrtc::RtpHeaderExtensionCapability("uri2", 3,
+                                           RtpTransceiverDirection::kSendOnly)};
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video1",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  opts.media_description_options.back().header_extensions = {
+      webrtc::RtpHeaderExtensionCapability("uri1", 1,
+                                           RtpTransceiverDirection::kStopped),
+      webrtc::RtpHeaderExtensionCapability("uri3", 7,
+                                           RtpTransceiverDirection::kSendOnly)};
+  auto offer = f1_.CreateOffer(opts, nullptr);
+  EXPECT_THAT(
+      offer->contents(),
+      ElementsAre(
+          Property(&ContentInfo::media_description,
+                   Pointee(Property(
+                       &MediaContentDescription::rtp_header_extensions,
+                       ElementsAre(Field(&RtpExtension::uri, "uri2"))))),
+          Property(&ContentInfo::media_description,
+                   Pointee(Property(
+                       &MediaContentDescription::rtp_header_extensions,
+                       ElementsAre(Field(&RtpExtension::uri, "uri3")))))));
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       OffersUnstoppedExtensionsWithAudioExtensionStopped) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  opts.media_description_options.back().header_extensions = {
+      webrtc::RtpHeaderExtensionCapability("uri1", 1,
+                                           RtpTransceiverDirection::kSendOnly),
+      webrtc::RtpHeaderExtensionCapability("uri2", 3,
+                                           RtpTransceiverDirection::kStopped)};
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video1",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  opts.media_description_options.back().header_extensions = {
+      webrtc::RtpHeaderExtensionCapability("uri42", 42,
+                                           RtpTransceiverDirection::kSendRecv),
+      webrtc::RtpHeaderExtensionCapability("uri3", 7,
+                                           RtpTransceiverDirection::kSendOnly)};
+  auto offer = f1_.CreateOffer(opts, nullptr);
+  EXPECT_THAT(
+      offer->contents(),
+      ElementsAre(
+          Property(&ContentInfo::media_description,
+                   Pointee(Property(
+                       &MediaContentDescription::rtp_header_extensions,
+                       ElementsAre(Field(&RtpExtension::uri, "uri1"))))),
+          Property(
+              &ContentInfo::media_description,
+              Pointee(Property(
+                  &MediaContentDescription::rtp_header_extensions,
+                  UnorderedElementsAre(Field(&RtpExtension::uri, "uri3"),
+                                       Field(&RtpExtension::uri, "uri42")))))));
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       OffersUnstoppedExtensionsWithVideoExtensionStopped) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  opts.media_description_options.back().header_extensions = {
+      webrtc::RtpHeaderExtensionCapability("uri1", 5,
+                                           RtpTransceiverDirection::kSendOnly),
+      webrtc::RtpHeaderExtensionCapability("uri2", 7,
+                                           RtpTransceiverDirection::kSendRecv)};
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video1",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  opts.media_description_options.back().header_extensions = {
+      webrtc::RtpHeaderExtensionCapability("uri42", 42,
+                                           RtpTransceiverDirection::kSendRecv),
+      webrtc::RtpHeaderExtensionCapability("uri3", 7,
+                                           RtpTransceiverDirection::kStopped)};
+  auto offer = f1_.CreateOffer(opts, nullptr);
+  EXPECT_THAT(
+      offer->contents(),
+      ElementsAre(
+          Property(
+              &ContentInfo::media_description,
+              Pointee(Property(
+                  &MediaContentDescription::rtp_header_extensions,
+                  UnorderedElementsAre(Field(&RtpExtension::uri, "uri1"),
+                                       Field(&RtpExtension::uri, "uri2"))))),
+          Property(&ContentInfo::media_description,
+                   Pointee(Property(
+                       &MediaContentDescription::rtp_header_extensions,
+                       ElementsAre(Field(&RtpExtension::uri, "uri42")))))));
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest, AnswersUnstoppedExtensions) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  opts.media_description_options.back().header_extensions = {
+      webrtc::RtpHeaderExtensionCapability("uri1", 4,
+                                           RtpTransceiverDirection::kStopped),
+      webrtc::RtpHeaderExtensionCapability("uri2", 3,
+                                           RtpTransceiverDirection::kSendOnly),
+      webrtc::RtpHeaderExtensionCapability("uri3", 2,
+                                           RtpTransceiverDirection::kRecvOnly),
+      webrtc::RtpHeaderExtensionCapability("uri4", 1,
+                                           RtpTransceiverDirection::kSendRecv)};
+  auto offer = f1_.CreateOffer(opts, nullptr);
+  opts.media_description_options.back().header_extensions = {
+      webrtc::RtpHeaderExtensionCapability("uri1", 4,
+                                           RtpTransceiverDirection::kSendOnly),
+      webrtc::RtpHeaderExtensionCapability("uri2", 3,
+                                           RtpTransceiverDirection::kRecvOnly),
+      webrtc::RtpHeaderExtensionCapability("uri3", 2,
+                                           RtpTransceiverDirection::kStopped),
+      webrtc::RtpHeaderExtensionCapability("uri4", 1,
+                                           RtpTransceiverDirection::kSendRecv)};
+  auto answer = f2_.CreateAnswer(offer.get(), opts, nullptr);
+  EXPECT_THAT(
+      answer->contents(),
+      ElementsAre(Property(
+          &ContentInfo::media_description,
+          Pointee(Property(&MediaContentDescription::rtp_header_extensions,
+                           ElementsAre(Field(&RtpExtension::uri, "uri2"),
+                                       Field(&RtpExtension::uri, "uri4")))))));
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       AppendsUnstoppedExtensionsToCurrentDescription) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  opts.media_description_options.back().header_extensions = {
+      webrtc::RtpHeaderExtensionCapability("uri1", 1,
+                                           RtpTransceiverDirection::kSendRecv)};
+  auto offer = f1_.CreateOffer(opts, nullptr);
+  opts.media_description_options.back().header_extensions = {
+      webrtc::RtpHeaderExtensionCapability("uri1", 2,
+                                           RtpTransceiverDirection::kSendRecv),
+      webrtc::RtpHeaderExtensionCapability("uri2", 3,
+                                           RtpTransceiverDirection::kRecvOnly),
+      webrtc::RtpHeaderExtensionCapability("uri3", 5,
+                                           RtpTransceiverDirection::kStopped),
+      webrtc::RtpHeaderExtensionCapability("uri4", 6,
+                                           RtpTransceiverDirection::kSendRecv)};
+  auto offer2 = f1_.CreateOffer(opts, offer.get());
+  EXPECT_THAT(
+      offer2->contents(),
+      ElementsAre(Property(
+          &ContentInfo::media_description,
+          Pointee(Property(&MediaContentDescription::rtp_header_extensions,
+                           ElementsAre(Field(&RtpExtension::uri, "uri1"),
+                                       Field(&RtpExtension::uri, "uri2"),
+                                       Field(&RtpExtension::uri, "uri4")))))));
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       AppendsStoppedExtensionIfKnownAndPresentInTheOffer) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  opts.media_description_options.back().header_extensions = {
+      webrtc::RtpHeaderExtensionCapability("uri1", 1,
+                                           RtpTransceiverDirection::kSendRecv),
+      webrtc::RtpHeaderExtensionCapability("uri2", 1,
+                                           RtpTransceiverDirection::kSendRecv)};
+  auto offer = f1_.CreateOffer(opts, nullptr);
+
+  // Now add "uri2" as stopped to the options verify that the offer contains
+  // uri2 since it's already present since before.
+  opts.media_description_options.back().header_extensions = {
+      webrtc::RtpHeaderExtensionCapability("uri1", 1,
+                                           RtpTransceiverDirection::kSendRecv),
+      webrtc::RtpHeaderExtensionCapability("uri2", 2,
+                                           RtpTransceiverDirection::kStopped)};
+  auto offer2 = f1_.CreateOffer(opts, offer.get());
+  EXPECT_THAT(
+      offer2->contents(),
+      ElementsAre(Property(
+          &ContentInfo::media_description,
+          Pointee(Property(&MediaContentDescription::rtp_header_extensions,
+                           ElementsAre(Field(&RtpExtension::uri, "uri1"),
+                                       Field(&RtpExtension::uri, "uri2")))))));
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestOfferAnswerWithEncryptedRtpExtensionsBoth) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+
+  f1_.set_enable_encrypted_rtp_header_extensions(true);
+  f2_.set_enable_encrypted_rtp_header_extensions(true);
+
+  SetAudioVideoRtpHeaderExtensions(MAKE_VECTOR(kAudioRtpExtension1),
+                                   MAKE_VECTOR(kVideoRtpExtension1), &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  SetAudioVideoRtpHeaderExtensions(MAKE_VECTOR(kAudioRtpExtension2),
+                                   MAKE_VECTOR(kVideoRtpExtension2), &opts);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+
+  EXPECT_EQ(
+      MAKE_VECTOR(kAudioRtpExtensionEncrypted1),
+      GetFirstAudioContentDescription(offer.get())->rtp_header_extensions());
+  EXPECT_EQ(
+      MAKE_VECTOR(kVideoRtpExtensionEncrypted1),
+      GetFirstVideoContentDescription(offer.get())->rtp_header_extensions());
+  EXPECT_EQ(
+      MAKE_VECTOR(kAudioRtpExtensionEncryptedAnswer),
+      GetFirstAudioContentDescription(answer.get())->rtp_header_extensions());
+  EXPECT_EQ(
+      MAKE_VECTOR(kVideoRtpExtensionEncryptedAnswer),
+      GetFirstVideoContentDescription(answer.get())->rtp_header_extensions());
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestOfferAnswerWithEncryptedRtpExtensionsOffer) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+
+  f1_.set_enable_encrypted_rtp_header_extensions(true);
+
+  SetAudioVideoRtpHeaderExtensions(MAKE_VECTOR(kAudioRtpExtension1),
+                                   MAKE_VECTOR(kVideoRtpExtension1), &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  SetAudioVideoRtpHeaderExtensions(MAKE_VECTOR(kAudioRtpExtension2),
+                                   MAKE_VECTOR(kVideoRtpExtension2), &opts);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+
+  EXPECT_EQ(
+      MAKE_VECTOR(kAudioRtpExtensionEncrypted1),
+      GetFirstAudioContentDescription(offer.get())->rtp_header_extensions());
+  EXPECT_EQ(
+      MAKE_VECTOR(kVideoRtpExtensionEncrypted1),
+      GetFirstVideoContentDescription(offer.get())->rtp_header_extensions());
+  EXPECT_EQ(
+      MAKE_VECTOR(kAudioRtpExtensionAnswer),
+      GetFirstAudioContentDescription(answer.get())->rtp_header_extensions());
+  EXPECT_EQ(
+      MAKE_VECTOR(kVideoRtpExtensionAnswer),
+      GetFirstVideoContentDescription(answer.get())->rtp_header_extensions());
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestOfferAnswerWithEncryptedRtpExtensionsAnswer) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+
+  f2_.set_enable_encrypted_rtp_header_extensions(true);
+
+  SetAudioVideoRtpHeaderExtensions(MAKE_VECTOR(kAudioRtpExtension1),
+                                   MAKE_VECTOR(kVideoRtpExtension1), &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  SetAudioVideoRtpHeaderExtensions(MAKE_VECTOR(kAudioRtpExtension2),
+                                   MAKE_VECTOR(kVideoRtpExtension2), &opts);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+
+  EXPECT_EQ(
+      MAKE_VECTOR(kAudioRtpExtension1),
+      GetFirstAudioContentDescription(offer.get())->rtp_header_extensions());
+  EXPECT_EQ(
+      MAKE_VECTOR(kVideoRtpExtension1),
+      GetFirstVideoContentDescription(offer.get())->rtp_header_extensions());
+  EXPECT_EQ(
+      MAKE_VECTOR(kAudioRtpExtensionAnswer),
+      GetFirstAudioContentDescription(answer.get())->rtp_header_extensions());
+  EXPECT_EQ(
+      MAKE_VECTOR(kVideoRtpExtensionAnswer),
+      GetFirstVideoContentDescription(answer.get())->rtp_header_extensions());
+}
+
+// Create an audio, video, data answer without legacy StreamParams.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestCreateAnswerWithoutLegacyStreams) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+  const ContentInfo* ac = answer->GetContentByName("audio");
+  const ContentInfo* vc = answer->GetContentByName("video");
+  ASSERT_TRUE(ac != NULL);
+  ASSERT_TRUE(vc != NULL);
+  const AudioContentDescription* acd = ac->media_description()->as_audio();
+  const VideoContentDescription* vcd = vc->media_description()->as_video();
+
+  EXPECT_FALSE(acd->has_ssrcs());  // No StreamParams.
+  EXPECT_FALSE(vcd->has_ssrcs());  // No StreamParams.
+}
+
+// Create a typical video answer, and ensure it matches what we expect.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateVideoAnswerRtcpMux) {
+  MediaSessionOptions offer_opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kSendRecv, &offer_opts);
+
+  MediaSessionOptions answer_opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kSendRecv, &answer_opts);
+
+  std::unique_ptr<SessionDescription> offer;
+  std::unique_ptr<SessionDescription> answer;
+
+  offer_opts.rtcp_mux_enabled = true;
+  answer_opts.rtcp_mux_enabled = true;
+  offer = f1_.CreateOffer(offer_opts, NULL);
+  answer = f2_.CreateAnswer(offer.get(), answer_opts, NULL);
+  ASSERT_TRUE(NULL != GetFirstAudioContentDescription(offer.get()));
+  ASSERT_TRUE(NULL != GetFirstVideoContentDescription(offer.get()));
+  ASSERT_TRUE(NULL != GetFirstAudioContentDescription(answer.get()));
+  ASSERT_TRUE(NULL != GetFirstVideoContentDescription(answer.get()));
+  EXPECT_TRUE(GetFirstAudioContentDescription(offer.get())->rtcp_mux());
+  EXPECT_TRUE(GetFirstVideoContentDescription(offer.get())->rtcp_mux());
+  EXPECT_TRUE(GetFirstAudioContentDescription(answer.get())->rtcp_mux());
+  EXPECT_TRUE(GetFirstVideoContentDescription(answer.get())->rtcp_mux());
+
+  offer_opts.rtcp_mux_enabled = true;
+  answer_opts.rtcp_mux_enabled = false;
+  offer = f1_.CreateOffer(offer_opts, NULL);
+  answer = f2_.CreateAnswer(offer.get(), answer_opts, NULL);
+  ASSERT_TRUE(NULL != GetFirstAudioContentDescription(offer.get()));
+  ASSERT_TRUE(NULL != GetFirstVideoContentDescription(offer.get()));
+  ASSERT_TRUE(NULL != GetFirstAudioContentDescription(answer.get()));
+  ASSERT_TRUE(NULL != GetFirstVideoContentDescription(answer.get()));
+  EXPECT_TRUE(GetFirstAudioContentDescription(offer.get())->rtcp_mux());
+  EXPECT_TRUE(GetFirstVideoContentDescription(offer.get())->rtcp_mux());
+  EXPECT_FALSE(GetFirstAudioContentDescription(answer.get())->rtcp_mux());
+  EXPECT_FALSE(GetFirstVideoContentDescription(answer.get())->rtcp_mux());
+
+  offer_opts.rtcp_mux_enabled = false;
+  answer_opts.rtcp_mux_enabled = true;
+  offer = f1_.CreateOffer(offer_opts, NULL);
+  answer = f2_.CreateAnswer(offer.get(), answer_opts, NULL);
+  ASSERT_TRUE(NULL != GetFirstAudioContentDescription(offer.get()));
+  ASSERT_TRUE(NULL != GetFirstVideoContentDescription(offer.get()));
+  ASSERT_TRUE(NULL != GetFirstAudioContentDescription(answer.get()));
+  ASSERT_TRUE(NULL != GetFirstVideoContentDescription(answer.get()));
+  EXPECT_FALSE(GetFirstAudioContentDescription(offer.get())->rtcp_mux());
+  EXPECT_FALSE(GetFirstVideoContentDescription(offer.get())->rtcp_mux());
+  EXPECT_FALSE(GetFirstAudioContentDescription(answer.get())->rtcp_mux());
+  EXPECT_FALSE(GetFirstVideoContentDescription(answer.get())->rtcp_mux());
+
+  offer_opts.rtcp_mux_enabled = false;
+  answer_opts.rtcp_mux_enabled = false;
+  offer = f1_.CreateOffer(offer_opts, NULL);
+  answer = f2_.CreateAnswer(offer.get(), answer_opts, NULL);
+  ASSERT_TRUE(NULL != GetFirstAudioContentDescription(offer.get()));
+  ASSERT_TRUE(NULL != GetFirstVideoContentDescription(offer.get()));
+  ASSERT_TRUE(NULL != GetFirstAudioContentDescription(answer.get()));
+  ASSERT_TRUE(NULL != GetFirstVideoContentDescription(answer.get()));
+  EXPECT_FALSE(GetFirstAudioContentDescription(offer.get())->rtcp_mux());
+  EXPECT_FALSE(GetFirstVideoContentDescription(offer.get())->rtcp_mux());
+  EXPECT_FALSE(GetFirstAudioContentDescription(answer.get())->rtcp_mux());
+  EXPECT_FALSE(GetFirstVideoContentDescription(answer.get())->rtcp_mux());
+}
+
+// Create an audio-only answer to a video offer.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateAudioAnswerToVideo) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+
+  opts.media_description_options[1].stopped = true;
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+  const ContentInfo* ac = answer->GetContentByName("audio");
+  const ContentInfo* vc = answer->GetContentByName("video");
+  ASSERT_TRUE(ac != NULL);
+  ASSERT_TRUE(vc != NULL);
+  ASSERT_TRUE(vc->media_description() != NULL);
+  EXPECT_TRUE(vc->rejected);
+}
+
+// Create an answer that rejects the contents which are rejected in the offer.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       CreateAnswerToOfferWithRejectedMedia) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  ContentInfo* ac = offer->GetContentByName("audio");
+  ContentInfo* vc = offer->GetContentByName("video");
+  ASSERT_TRUE(ac != NULL);
+  ASSERT_TRUE(vc != NULL);
+  ac->rejected = true;
+  vc->rejected = true;
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+  ac = answer->GetContentByName("audio");
+  vc = answer->GetContentByName("video");
+  ASSERT_TRUE(ac != NULL);
+  ASSERT_TRUE(vc != NULL);
+  EXPECT_TRUE(ac->rejected);
+  EXPECT_TRUE(vc->rejected);
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       OfferAndAnswerDoesNotHaveMixedByteSessionAttribute) {
+  MediaSessionOptions opts;
+  std::unique_ptr<SessionDescription> offer =
+      f1_.CreateOffer(opts, /*current_description=*/nullptr);
+  offer->set_extmap_allow_mixed(false);
+
+  std::unique_ptr<SessionDescription> answer(
+      f2_.CreateAnswer(offer.get(), opts, /*current_description=*/nullptr));
+
+  EXPECT_FALSE(answer->extmap_allow_mixed());
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       OfferAndAnswerHaveMixedByteSessionAttribute) {
+  MediaSessionOptions opts;
+  std::unique_ptr<SessionDescription> offer =
+      f1_.CreateOffer(opts, /*current_description=*/nullptr);
+  offer->set_extmap_allow_mixed(true);
+
+  std::unique_ptr<SessionDescription> answer_support(
+      f2_.CreateAnswer(offer.get(), opts, /*current_description=*/nullptr));
+
+  EXPECT_TRUE(answer_support->extmap_allow_mixed());
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       OfferAndAnswerDoesNotHaveMixedByteMediaAttributes) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kSendRecv, &opts);
+  std::unique_ptr<SessionDescription> offer =
+      f1_.CreateOffer(opts, /*current_description=*/nullptr);
+  offer->set_extmap_allow_mixed(false);
+  MediaContentDescription* audio_offer =
+      offer->GetContentDescriptionByName("audio");
+  MediaContentDescription* video_offer =
+      offer->GetContentDescriptionByName("video");
+  ASSERT_EQ(MediaContentDescription::kNo,
+            audio_offer->extmap_allow_mixed_enum());
+  ASSERT_EQ(MediaContentDescription::kNo,
+            video_offer->extmap_allow_mixed_enum());
+
+  std::unique_ptr<SessionDescription> answer(
+      f2_.CreateAnswer(offer.get(), opts, /*current_description=*/nullptr));
+
+  MediaContentDescription* audio_answer =
+      answer->GetContentDescriptionByName("audio");
+  MediaContentDescription* video_answer =
+      answer->GetContentDescriptionByName("video");
+  EXPECT_EQ(MediaContentDescription::kNo,
+            audio_answer->extmap_allow_mixed_enum());
+  EXPECT_EQ(MediaContentDescription::kNo,
+            video_answer->extmap_allow_mixed_enum());
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       OfferAndAnswerHaveSameMixedByteMediaAttributes) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kSendRecv, &opts);
+  std::unique_ptr<SessionDescription> offer =
+      f1_.CreateOffer(opts, /*current_description=*/nullptr);
+  offer->set_extmap_allow_mixed(false);
+  MediaContentDescription* audio_offer =
+      offer->GetContentDescriptionByName("audio");
+  audio_offer->set_extmap_allow_mixed_enum(MediaContentDescription::kMedia);
+  MediaContentDescription* video_offer =
+      offer->GetContentDescriptionByName("video");
+  video_offer->set_extmap_allow_mixed_enum(MediaContentDescription::kMedia);
+
+  std::unique_ptr<SessionDescription> answer(
+      f2_.CreateAnswer(offer.get(), opts, /*current_description=*/nullptr));
+
+  MediaContentDescription* audio_answer =
+      answer->GetContentDescriptionByName("audio");
+  MediaContentDescription* video_answer =
+      answer->GetContentDescriptionByName("video");
+  EXPECT_EQ(MediaContentDescription::kMedia,
+            audio_answer->extmap_allow_mixed_enum());
+  EXPECT_EQ(MediaContentDescription::kMedia,
+            video_answer->extmap_allow_mixed_enum());
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       OfferAndAnswerHaveDifferentMixedByteMediaAttributes) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kSendRecv, &opts);
+  std::unique_ptr<SessionDescription> offer =
+      f1_.CreateOffer(opts, /*current_description=*/nullptr);
+  offer->set_extmap_allow_mixed(false);
+  MediaContentDescription* audio_offer =
+      offer->GetContentDescriptionByName("audio");
+  audio_offer->set_extmap_allow_mixed_enum(MediaContentDescription::kNo);
+  MediaContentDescription* video_offer =
+      offer->GetContentDescriptionByName("video");
+  video_offer->set_extmap_allow_mixed_enum(MediaContentDescription::kMedia);
+
+  std::unique_ptr<SessionDescription> answer(
+      f2_.CreateAnswer(offer.get(), opts, /*current_description=*/nullptr));
+
+  MediaContentDescription* audio_answer =
+      answer->GetContentDescriptionByName("audio");
+  MediaContentDescription* video_answer =
+      answer->GetContentDescriptionByName("video");
+  EXPECT_EQ(MediaContentDescription::kNo,
+            audio_answer->extmap_allow_mixed_enum());
+  EXPECT_EQ(MediaContentDescription::kMedia,
+            video_answer->extmap_allow_mixed_enum());
+}
+
+// Create an audio and video offer with:
+// - one video track
+// - two audio tracks
+// and ensure it matches what we expect. Also updates the initial offer by
+// adding a new video track and replaces one of the audio tracks.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateMultiStreamVideoOffer) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kSendRecv, &opts);
+  AttachSenderToMediaDescriptionOptions("video", MEDIA_TYPE_VIDEO, kVideoTrack1,
+                                        {kMediaStream1}, 1, &opts);
+  AttachSenderToMediaDescriptionOptions("audio", MEDIA_TYPE_AUDIO, kAudioTrack1,
+                                        {kMediaStream1}, 1, &opts);
+  AttachSenderToMediaDescriptionOptions("audio", MEDIA_TYPE_AUDIO, kAudioTrack2,
+                                        {kMediaStream1}, 1, &opts);
+
+  f1_.set_secure(SEC_ENABLED);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+
+  ASSERT_TRUE(offer.get() != NULL);
+  const ContentInfo* ac = offer->GetContentByName("audio");
+  const ContentInfo* vc = offer->GetContentByName("video");
+  ASSERT_TRUE(ac != NULL);
+  ASSERT_TRUE(vc != NULL);
+  const AudioContentDescription* acd = ac->media_description()->as_audio();
+  const VideoContentDescription* vcd = vc->media_description()->as_video();
+  EXPECT_EQ(MEDIA_TYPE_AUDIO, acd->type());
+  EXPECT_EQ(f1_.audio_sendrecv_codecs(), acd->codecs());
+
+  const StreamParamsVec& audio_streams = acd->streams();
+  ASSERT_EQ(2U, audio_streams.size());
+  EXPECT_EQ(audio_streams[0].cname, audio_streams[1].cname);
+  EXPECT_EQ(kAudioTrack1, audio_streams[0].id);
+  ASSERT_EQ(1U, audio_streams[0].ssrcs.size());
+  EXPECT_NE(0U, audio_streams[0].ssrcs[0]);
+  EXPECT_EQ(kAudioTrack2, audio_streams[1].id);
+  ASSERT_EQ(1U, audio_streams[1].ssrcs.size());
+  EXPECT_NE(0U, audio_streams[1].ssrcs[0]);
+
+  EXPECT_EQ(kAutoBandwidth, acd->bandwidth());  // default bandwidth (auto)
+  EXPECT_TRUE(acd->rtcp_mux());                 // rtcp-mux defaults on
+  ASSERT_CRYPTO(acd, 1U, kDefaultSrtpCryptoSuite);
+
+  EXPECT_EQ(MEDIA_TYPE_VIDEO, vcd->type());
+  EXPECT_EQ(f1_.video_sendrecv_codecs(), vcd->codecs());
+  ASSERT_CRYPTO(vcd, 1U, kDefaultSrtpCryptoSuite);
+
+  const StreamParamsVec& video_streams = vcd->streams();
+  ASSERT_EQ(1U, video_streams.size());
+  EXPECT_EQ(video_streams[0].cname, audio_streams[0].cname);
+  EXPECT_EQ(kVideoTrack1, video_streams[0].id);
+  EXPECT_EQ(kAutoBandwidth, vcd->bandwidth());  // default bandwidth (auto)
+  EXPECT_TRUE(vcd->rtcp_mux());                 // rtcp-mux defaults on
+
+  // Update the offer. Add a new video track that is not synched to the
+  // other tracks and replace audio track 2 with audio track 3.
+  AttachSenderToMediaDescriptionOptions("video", MEDIA_TYPE_VIDEO, kVideoTrack2,
+                                        {kMediaStream2}, 1, &opts);
+  DetachSenderFromMediaSection("audio", kAudioTrack2, &opts);
+  AttachSenderToMediaDescriptionOptions("audio", MEDIA_TYPE_AUDIO, kAudioTrack3,
+                                        {kMediaStream1}, 1, &opts);
+  std::unique_ptr<SessionDescription> updated_offer(
+      f1_.CreateOffer(opts, offer.get()));
+
+  ASSERT_TRUE(updated_offer.get() != NULL);
+  ac = updated_offer->GetContentByName("audio");
+  vc = updated_offer->GetContentByName("video");
+  ASSERT_TRUE(ac != NULL);
+  ASSERT_TRUE(vc != NULL);
+  const AudioContentDescription* updated_acd =
+      ac->media_description()->as_audio();
+  const VideoContentDescription* updated_vcd =
+      vc->media_description()->as_video();
+
+  EXPECT_EQ(acd->type(), updated_acd->type());
+  EXPECT_EQ(acd->codecs(), updated_acd->codecs());
+  EXPECT_EQ(vcd->type(), updated_vcd->type());
+  EXPECT_EQ(vcd->codecs(), updated_vcd->codecs());
+  ASSERT_CRYPTO(updated_acd, 1U, kDefaultSrtpCryptoSuite);
+  EXPECT_TRUE(CompareCryptoParams(acd->cryptos(), updated_acd->cryptos()));
+  ASSERT_CRYPTO(updated_vcd, 1U, kDefaultSrtpCryptoSuite);
+  EXPECT_TRUE(CompareCryptoParams(vcd->cryptos(), updated_vcd->cryptos()));
+
+  const StreamParamsVec& updated_audio_streams = updated_acd->streams();
+  ASSERT_EQ(2U, updated_audio_streams.size());
+  EXPECT_EQ(audio_streams[0], updated_audio_streams[0]);
+  EXPECT_EQ(kAudioTrack3, updated_audio_streams[1].id);  // New audio track.
+  ASSERT_EQ(1U, updated_audio_streams[1].ssrcs.size());
+  EXPECT_NE(0U, updated_audio_streams[1].ssrcs[0]);
+  EXPECT_EQ(updated_audio_streams[0].cname, updated_audio_streams[1].cname);
+
+  const StreamParamsVec& updated_video_streams = updated_vcd->streams();
+  ASSERT_EQ(2U, updated_video_streams.size());
+  EXPECT_EQ(video_streams[0], updated_video_streams[0]);
+  EXPECT_EQ(kVideoTrack2, updated_video_streams[1].id);
+  // All the media streams in one PeerConnection share one RTCP CNAME.
+  EXPECT_EQ(updated_video_streams[1].cname, updated_video_streams[0].cname);
+}
+
+// Create an offer with simulcast video stream.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateSimulcastVideoOffer) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  const int num_sim_layers = 3;
+  AttachSenderToMediaDescriptionOptions("video", MEDIA_TYPE_VIDEO, kVideoTrack1,
+                                        {kMediaStream1}, num_sim_layers, &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+
+  ASSERT_TRUE(offer.get() != NULL);
+  const ContentInfo* vc = offer->GetContentByName("video");
+  ASSERT_TRUE(vc != NULL);
+  const VideoContentDescription* vcd = vc->media_description()->as_video();
+
+  const StreamParamsVec& video_streams = vcd->streams();
+  ASSERT_EQ(1U, video_streams.size());
+  EXPECT_EQ(kVideoTrack1, video_streams[0].id);
+  const SsrcGroup* sim_ssrc_group =
+      video_streams[0].get_ssrc_group(cricket::kSimSsrcGroupSemantics);
+  ASSERT_TRUE(sim_ssrc_group != NULL);
+  EXPECT_EQ(static_cast<size_t>(num_sim_layers), sim_ssrc_group->ssrcs.size());
+}
+
+MATCHER(RidDescriptionEquals, "Verifies that two RidDescriptions are equal.") {
+  const RidDescription& rid1 = ::testing::get<0>(arg);
+  const RidDescription& rid2 = ::testing::get<1>(arg);
+  return rid1.rid == rid2.rid && rid1.direction == rid2.direction;
+}
+
+static void CheckSimulcastInSessionDescription(
+    const SessionDescription* description,
+    const std::string& content_name,
+    const std::vector<RidDescription>& send_rids,
+    const SimulcastLayerList& send_layers) {
+  ASSERT_NE(description, nullptr);
+  const ContentInfo* content = description->GetContentByName(content_name);
+  ASSERT_NE(content, nullptr);
+  const MediaContentDescription* cd = content->media_description();
+  ASSERT_NE(cd, nullptr);
+  const StreamParamsVec& streams = cd->streams();
+  ASSERT_THAT(streams, SizeIs(1));
+  const StreamParams& stream = streams[0];
+  ASSERT_THAT(stream.ssrcs, IsEmpty());
+  EXPECT_TRUE(stream.has_rids());
+  const std::vector<RidDescription> rids = stream.rids();
+
+  EXPECT_THAT(rids, Pointwise(RidDescriptionEquals(), send_rids));
+
+  EXPECT_TRUE(cd->HasSimulcast());
+  const SimulcastDescription& simulcast = cd->simulcast_description();
+  EXPECT_THAT(simulcast.send_layers(), SizeIs(send_layers.size()));
+  EXPECT_THAT(simulcast.send_layers(), Pointwise(Eq(), send_layers));
+
+  ASSERT_THAT(simulcast.receive_layers().GetAllLayers(), SizeIs(0));
+}
+
+// Create an offer with spec-compliant simulcast video stream.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateCompliantSimulcastOffer) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  std::vector<RidDescription> send_rids;
+  send_rids.push_back(RidDescription("f", RidDirection::kSend));
+  send_rids.push_back(RidDescription("h", RidDirection::kSend));
+  send_rids.push_back(RidDescription("q", RidDirection::kSend));
+  SimulcastLayerList simulcast_layers;
+  simulcast_layers.AddLayer(SimulcastLayer(send_rids[0].rid, false));
+  simulcast_layers.AddLayer(SimulcastLayer(send_rids[1].rid, true));
+  simulcast_layers.AddLayer(SimulcastLayer(send_rids[2].rid, false));
+  AttachSenderToMediaDescriptionOptions("video", MEDIA_TYPE_VIDEO, kVideoTrack1,
+                                        {kMediaStream1}, send_rids,
+                                        simulcast_layers, 0, &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+
+  CheckSimulcastInSessionDescription(offer.get(), "video", send_rids,
+                                     simulcast_layers);
+}
+
+// Create an offer that signals RIDs (not SSRCs) without Simulcast.
+// In this scenario, RIDs do not need to be negotiated (there is only one).
+TEST_F(MediaSessionDescriptionFactoryTest, TestOfferWithRidsNoSimulcast) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  RidDescription rid("f", RidDirection::kSend);
+  AttachSenderToMediaDescriptionOptions("video", MEDIA_TYPE_VIDEO, kVideoTrack1,
+                                        {kMediaStream1}, {rid},
+                                        SimulcastLayerList(), 0, &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+
+  ASSERT_NE(offer.get(), nullptr);
+  const ContentInfo* content = offer->GetContentByName("video");
+  ASSERT_NE(content, nullptr);
+  const MediaContentDescription* cd = content->media_description();
+  ASSERT_NE(cd, nullptr);
+  const StreamParamsVec& streams = cd->streams();
+  ASSERT_THAT(streams, SizeIs(1));
+  const StreamParams& stream = streams[0];
+  ASSERT_THAT(stream.ssrcs, IsEmpty());
+  EXPECT_FALSE(stream.has_rids());
+  EXPECT_FALSE(cd->HasSimulcast());
+}
+
+// Create an answer with spec-compliant simulcast video stream.
+// In this scenario, the SFU is the caller requesting that we send Simulcast.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateCompliantSimulcastAnswer) {
+  MediaSessionOptions offer_opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &offer_opts);
+  AttachSenderToMediaDescriptionOptions("video", MEDIA_TYPE_VIDEO, kVideoTrack1,
+                                        {kMediaStream1}, 1, &offer_opts);
+  std::unique_ptr<SessionDescription> offer =
+      f1_.CreateOffer(offer_opts, nullptr);
+
+  MediaSessionOptions answer_opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &answer_opts);
+
+  std::vector<RidDescription> rid_descriptions{
+      RidDescription("f", RidDirection::kSend),
+      RidDescription("h", RidDirection::kSend),
+      RidDescription("q", RidDirection::kSend),
+  };
+  SimulcastLayerList simulcast_layers;
+  simulcast_layers.AddLayer(SimulcastLayer(rid_descriptions[0].rid, false));
+  simulcast_layers.AddLayer(SimulcastLayer(rid_descriptions[1].rid, true));
+  simulcast_layers.AddLayer(SimulcastLayer(rid_descriptions[2].rid, false));
+  AttachSenderToMediaDescriptionOptions("video", MEDIA_TYPE_VIDEO, kVideoTrack1,
+                                        {kMediaStream1}, rid_descriptions,
+                                        simulcast_layers, 0, &answer_opts);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), answer_opts, nullptr);
+
+  CheckSimulcastInSessionDescription(answer.get(), "video", rid_descriptions,
+                                     simulcast_layers);
+}
+
+// Create an answer that signals RIDs (not SSRCs) without Simulcast.
+// In this scenario, RIDs do not need to be negotiated (there is only one).
+// Note that RID Direction is not the same as the transceiver direction.
+TEST_F(MediaSessionDescriptionFactoryTest, TestAnswerWithRidsNoSimulcast) {
+  MediaSessionOptions offer_opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &offer_opts);
+  RidDescription rid_offer("f", RidDirection::kSend);
+  AttachSenderToMediaDescriptionOptions("video", MEDIA_TYPE_VIDEO, kVideoTrack1,
+                                        {kMediaStream1}, {rid_offer},
+                                        SimulcastLayerList(), 0, &offer_opts);
+  std::unique_ptr<SessionDescription> offer =
+      f1_.CreateOffer(offer_opts, nullptr);
+
+  MediaSessionOptions answer_opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &answer_opts);
+
+  RidDescription rid_answer("f", RidDirection::kReceive);
+  AttachSenderToMediaDescriptionOptions("video", MEDIA_TYPE_VIDEO, kVideoTrack1,
+                                        {kMediaStream1}, {rid_answer},
+                                        SimulcastLayerList(), 0, &answer_opts);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), answer_opts, nullptr);
+
+  ASSERT_NE(answer.get(), nullptr);
+  const ContentInfo* content = offer->GetContentByName("video");
+  ASSERT_NE(content, nullptr);
+  const MediaContentDescription* cd = content->media_description();
+  ASSERT_NE(cd, nullptr);
+  const StreamParamsVec& streams = cd->streams();
+  ASSERT_THAT(streams, SizeIs(1));
+  const StreamParams& stream = streams[0];
+  ASSERT_THAT(stream.ssrcs, IsEmpty());
+  EXPECT_FALSE(stream.has_rids());
+  EXPECT_FALSE(cd->HasSimulcast());
+}
+
+// Create an audio and video answer to a standard video offer with:
+// - one video track
+// - two audio tracks
+// - two data tracks
+// and ensure it matches what we expect. Also updates the initial answer by
+// adding a new video track and removes one of the audio tracks.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCreateMultiStreamVideoAnswer) {
+  MediaSessionOptions offer_opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &offer_opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &offer_opts);
+  f1_.set_secure(SEC_ENABLED);
+  f2_.set_secure(SEC_ENABLED);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(offer_opts, NULL);
+
+  MediaSessionOptions answer_opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &answer_opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &answer_opts);
+  AttachSenderToMediaDescriptionOptions("video", MEDIA_TYPE_VIDEO, kVideoTrack1,
+                                        {kMediaStream1}, 1, &answer_opts);
+  AttachSenderToMediaDescriptionOptions("audio", MEDIA_TYPE_AUDIO, kAudioTrack1,
+                                        {kMediaStream1}, 1, &answer_opts);
+  AttachSenderToMediaDescriptionOptions("audio", MEDIA_TYPE_AUDIO, kAudioTrack2,
+                                        {kMediaStream1}, 1, &answer_opts);
+
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), answer_opts, NULL);
+
+  ASSERT_TRUE(answer.get() != NULL);
+  const ContentInfo* ac = answer->GetContentByName("audio");
+  const ContentInfo* vc = answer->GetContentByName("video");
+  ASSERT_TRUE(ac != NULL);
+  ASSERT_TRUE(vc != NULL);
+  const AudioContentDescription* acd = ac->media_description()->as_audio();
+  const VideoContentDescription* vcd = vc->media_description()->as_video();
+  ASSERT_CRYPTO(acd, 1U, kDefaultSrtpCryptoSuite);
+  ASSERT_CRYPTO(vcd, 1U, kDefaultSrtpCryptoSuite);
+
+  EXPECT_EQ(MEDIA_TYPE_AUDIO, acd->type());
+  EXPECT_THAT(acd->codecs(), ElementsAreArray(kAudioCodecsAnswer));
+
+  const StreamParamsVec& audio_streams = acd->streams();
+  ASSERT_EQ(2U, audio_streams.size());
+  EXPECT_TRUE(audio_streams[0].cname == audio_streams[1].cname);
+  EXPECT_EQ(kAudioTrack1, audio_streams[0].id);
+  ASSERT_EQ(1U, audio_streams[0].ssrcs.size());
+  EXPECT_NE(0U, audio_streams[0].ssrcs[0]);
+  EXPECT_EQ(kAudioTrack2, audio_streams[1].id);
+  ASSERT_EQ(1U, audio_streams[1].ssrcs.size());
+  EXPECT_NE(0U, audio_streams[1].ssrcs[0]);
+
+  EXPECT_EQ(kAutoBandwidth, acd->bandwidth());  // default bandwidth (auto)
+  EXPECT_TRUE(acd->rtcp_mux());                 // rtcp-mux defaults on
+
+  EXPECT_EQ(MEDIA_TYPE_VIDEO, vcd->type());
+  EXPECT_THAT(vcd->codecs(), ElementsAreArray(kVideoCodecsAnswer));
+
+  const StreamParamsVec& video_streams = vcd->streams();
+  ASSERT_EQ(1U, video_streams.size());
+  EXPECT_EQ(video_streams[0].cname, audio_streams[0].cname);
+  EXPECT_EQ(kVideoTrack1, video_streams[0].id);
+  EXPECT_EQ(kAutoBandwidth, vcd->bandwidth());  // default bandwidth (auto)
+  EXPECT_TRUE(vcd->rtcp_mux());                 // rtcp-mux defaults on
+
+  // Update the answer. Add a new video track that is not synched to the
+  // other tracks and remove 1 audio track.
+  AttachSenderToMediaDescriptionOptions("video", MEDIA_TYPE_VIDEO, kVideoTrack2,
+                                        {kMediaStream2}, 1, &answer_opts);
+  DetachSenderFromMediaSection("audio", kAudioTrack2, &answer_opts);
+  std::unique_ptr<SessionDescription> updated_answer(
+      f2_.CreateAnswer(offer.get(), answer_opts, answer.get()));
+
+  ASSERT_TRUE(updated_answer.get() != NULL);
+  ac = updated_answer->GetContentByName("audio");
+  vc = updated_answer->GetContentByName("video");
+  ASSERT_TRUE(ac != NULL);
+  ASSERT_TRUE(vc != NULL);
+  const AudioContentDescription* updated_acd =
+      ac->media_description()->as_audio();
+  const VideoContentDescription* updated_vcd =
+      vc->media_description()->as_video();
+
+  ASSERT_CRYPTO(updated_acd, 1U, kDefaultSrtpCryptoSuite);
+  EXPECT_TRUE(CompareCryptoParams(acd->cryptos(), updated_acd->cryptos()));
+  ASSERT_CRYPTO(updated_vcd, 1U, kDefaultSrtpCryptoSuite);
+  EXPECT_TRUE(CompareCryptoParams(vcd->cryptos(), updated_vcd->cryptos()));
+
+  EXPECT_EQ(acd->type(), updated_acd->type());
+  EXPECT_EQ(acd->codecs(), updated_acd->codecs());
+  EXPECT_EQ(vcd->type(), updated_vcd->type());
+  EXPECT_EQ(vcd->codecs(), updated_vcd->codecs());
+
+  const StreamParamsVec& updated_audio_streams = updated_acd->streams();
+  ASSERT_EQ(1U, updated_audio_streams.size());
+  EXPECT_TRUE(audio_streams[0] == updated_audio_streams[0]);
+
+  const StreamParamsVec& updated_video_streams = updated_vcd->streams();
+  ASSERT_EQ(2U, updated_video_streams.size());
+  EXPECT_EQ(video_streams[0], updated_video_streams[0]);
+  EXPECT_EQ(kVideoTrack2, updated_video_streams[1].id);
+  // All media streams in one PeerConnection share one CNAME.
+  EXPECT_EQ(updated_video_streams[1].cname, updated_video_streams[0].cname);
+}
+
+// Create an updated offer after creating an answer to the original offer and
+// verify that the codecs that were part of the original answer are not changed
+// in the updated offer.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       RespondentCreatesOfferAfterCreatingAnswer) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+
+  const AudioContentDescription* acd =
+      GetFirstAudioContentDescription(answer.get());
+  EXPECT_THAT(acd->codecs(), ElementsAreArray(kAudioCodecsAnswer));
+
+  const VideoContentDescription* vcd =
+      GetFirstVideoContentDescription(answer.get());
+  EXPECT_THAT(vcd->codecs(), ElementsAreArray(kVideoCodecsAnswer));
+
+  std::unique_ptr<SessionDescription> updated_offer(
+      f2_.CreateOffer(opts, answer.get()));
+
+  // The expected audio codecs are the common audio codecs from the first
+  // offer/answer exchange plus the audio codecs only `f2_` offer, sorted in
+  // preference order.
+  // TODO(wu): `updated_offer` should not include the codec
+  // (i.e. `kAudioCodecs2[0]`) the other side doesn't support.
+  const AudioCodec kUpdatedAudioCodecOffer[] = {
+      kAudioCodecsAnswer[0],
+      kAudioCodecsAnswer[1],
+      kAudioCodecs2[0],
+  };
+
+  // The expected video codecs are the common video codecs from the first
+  // offer/answer exchange plus the video codecs only `f2_` offer, sorted in
+  // preference order.
+  const VideoCodec kUpdatedVideoCodecOffer[] = {
+      kVideoCodecsAnswer[0],
+      kVideoCodecs2[1],
+  };
+
+  const AudioContentDescription* updated_acd =
+      GetFirstAudioContentDescription(updated_offer.get());
+  EXPECT_THAT(updated_acd->codecs(), ElementsAreArray(kUpdatedAudioCodecOffer));
+
+  const VideoContentDescription* updated_vcd =
+      GetFirstVideoContentDescription(updated_offer.get());
+  EXPECT_THAT(updated_vcd->codecs(), ElementsAreArray(kUpdatedVideoCodecOffer));
+}
+
+// Test that a reoffer does not reuse audio codecs from a previous media section
+// that is being recycled.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       ReOfferDoesNotReUseRecycledAudioCodecs) {
+  f1_.set_video_codecs({}, {});
+  f2_.set_video_codecs({}, {});
+
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "a0",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+
+  // Recycle the media section by changing its mid.
+  opts.media_description_options[0].mid = "a1";
+  std::unique_ptr<SessionDescription> reoffer =
+      f2_.CreateOffer(opts, answer.get());
+
+  // Expect that the results of the first negotiation are ignored. If the m=
+  // section was not recycled the payload types would match the initial offerer.
+  const AudioContentDescription* acd =
+      GetFirstAudioContentDescription(reoffer.get());
+  EXPECT_THAT(acd->codecs(), ElementsAreArray(kAudioCodecs2));
+}
+
+// Test that a reoffer does not reuse video codecs from a previous media section
+// that is being recycled.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       ReOfferDoesNotReUseRecycledVideoCodecs) {
+  f1_.set_audio_codecs({}, {});
+  f2_.set_audio_codecs({}, {});
+
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "v0",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  auto answer = f2_.CreateAnswer(offer.get(), opts, nullptr);
+
+  // Recycle the media section by changing its mid.
+  opts.media_description_options[0].mid = "v1";
+  std::unique_ptr<SessionDescription> reoffer =
+      f2_.CreateOffer(opts, answer.get());
+
+  // Expect that the results of the first negotiation are ignored. If the m=
+  // section was not recycled the payload types would match the initial offerer.
+  const VideoContentDescription* vcd =
+      GetFirstVideoContentDescription(reoffer.get());
+  EXPECT_THAT(vcd->codecs(), ElementsAreArray(kVideoCodecs2));
+}
+
+// Test that a reanswer does not reuse audio codecs from a previous media
+// section that is being recycled.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       ReAnswerDoesNotReUseRecycledAudioCodecs) {
+  f1_.set_video_codecs({}, {});
+  f2_.set_video_codecs({}, {});
+
+  // Perform initial offer/answer in reverse (`f2_` as offerer) so that the
+  // second offer/answer is forward (`f1_` as offerer).
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "a0",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  std::unique_ptr<SessionDescription> offer = f2_.CreateOffer(opts, nullptr);
+  std::unique_ptr<SessionDescription> answer =
+      f1_.CreateAnswer(offer.get(), opts, nullptr);
+
+  // Recycle the media section by changing its mid.
+  opts.media_description_options[0].mid = "a1";
+  std::unique_ptr<SessionDescription> reoffer =
+      f1_.CreateOffer(opts, answer.get());
+  std::unique_ptr<SessionDescription> reanswer =
+      f2_.CreateAnswer(reoffer.get(), opts, offer.get());
+
+  // Expect that the results of the first negotiation are ignored. If the m=
+  // section was not recycled the payload types would match the initial offerer.
+  const AudioContentDescription* acd =
+      GetFirstAudioContentDescription(reanswer.get());
+  EXPECT_THAT(acd->codecs(), ElementsAreArray(kAudioCodecsAnswer));
+}
+
+// Test that a reanswer does not reuse video codecs from a previous media
+// section that is being recycled.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       ReAnswerDoesNotReUseRecycledVideoCodecs) {
+  f1_.set_audio_codecs({}, {});
+  f2_.set_audio_codecs({}, {});
+
+  // Perform initial offer/answer in reverse (`f2_` as offerer) so that the
+  // second offer/answer is forward (`f1_` as offerer).
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "v0",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  std::unique_ptr<SessionDescription> offer = f2_.CreateOffer(opts, nullptr);
+  std::unique_ptr<SessionDescription> answer =
+      f1_.CreateAnswer(offer.get(), opts, nullptr);
+
+  // Recycle the media section by changing its mid.
+  opts.media_description_options[0].mid = "v1";
+  std::unique_ptr<SessionDescription> reoffer =
+      f1_.CreateOffer(opts, answer.get());
+  std::unique_ptr<SessionDescription> reanswer =
+      f2_.CreateAnswer(reoffer.get(), opts, offer.get());
+
+  // Expect that the results of the first negotiation are ignored. If the m=
+  // section was not recycled the payload types would match the initial offerer.
+  const VideoContentDescription* vcd =
+      GetFirstVideoContentDescription(reanswer.get());
+  EXPECT_THAT(vcd->codecs(), ElementsAreArray(kVideoCodecsAnswer));
+}
+
+// Create an updated offer after creating an answer to the original offer and
+// verify that the codecs that were part of the original answer are not changed
+// in the updated offer. In this test Rtx is enabled.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       RespondentCreatesOfferAfterCreatingAnswerWithRtx) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &opts);
+  std::vector<VideoCodec> f1_codecs = MAKE_VECTOR(kVideoCodecs1);
+  // This creates rtx for H264 with the payload type `f1_` uses.
+  AddRtxCodec(VideoCodec::CreateRtxCodec(126, kVideoCodecs1[1].id), &f1_codecs);
+  f1_.set_video_codecs(f1_codecs, f1_codecs);
+
+  std::vector<VideoCodec> f2_codecs = MAKE_VECTOR(kVideoCodecs2);
+  // This creates rtx for H264 with the payload type `f2_` uses.
+  AddRtxCodec(VideoCodec::CreateRtxCodec(125, kVideoCodecs2[0].id), &f2_codecs);
+  f2_.set_video_codecs(f2_codecs, f2_codecs);
+
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+
+  const VideoContentDescription* vcd =
+      GetFirstVideoContentDescription(answer.get());
+
+  std::vector<VideoCodec> expected_codecs = MAKE_VECTOR(kVideoCodecsAnswer);
+  AddRtxCodec(VideoCodec::CreateRtxCodec(126, kVideoCodecs1[1].id),
+              &expected_codecs);
+
+  EXPECT_EQ(expected_codecs, vcd->codecs());
+
+  // Now, make sure we get same result (except for the order) if `f2_` creates
+  // an updated offer even though the default payload types between `f1_` and
+  // `f2_` are different.
+  std::unique_ptr<SessionDescription> updated_offer(
+      f2_.CreateOffer(opts, answer.get()));
+  ASSERT_TRUE(updated_offer);
+  std::unique_ptr<SessionDescription> updated_answer(
+      f1_.CreateAnswer(updated_offer.get(), opts, answer.get()));
+
+  const VideoContentDescription* updated_vcd =
+      GetFirstVideoContentDescription(updated_answer.get());
+
+  EXPECT_EQ(expected_codecs, updated_vcd->codecs());
+}
+
+// Regression test for:
+// https://bugs.chromium.org/p/webrtc/issues/detail?id=8332
+// Existing codecs should always appear before new codecs in re-offers. But
+// under a specific set of circumstances, the existing RTX codec was ending up
+// added to the end of the list.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       RespondentCreatesOfferAfterCreatingAnswerWithRemappedRtxPayloadType) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &opts);
+  // We specifically choose different preferred payload types for VP8 to
+  // trigger the issue.
+  cricket::VideoCodec vp8_offerer(100, "VP8");
+  cricket::VideoCodec vp8_offerer_rtx =
+      VideoCodec::CreateRtxCodec(101, vp8_offerer.id);
+  cricket::VideoCodec vp8_answerer(110, "VP8");
+  cricket::VideoCodec vp8_answerer_rtx =
+      VideoCodec::CreateRtxCodec(111, vp8_answerer.id);
+  cricket::VideoCodec vp9(120, "VP9");
+  cricket::VideoCodec vp9_rtx = VideoCodec::CreateRtxCodec(121, vp9.id);
+
+  std::vector<VideoCodec> f1_codecs = {vp8_offerer, vp8_offerer_rtx};
+  // We also specifically cause the answerer to prefer VP9, such that if it
+  // *doesn't* honor the existing preferred codec (VP8) we'll notice.
+  std::vector<VideoCodec> f2_codecs = {vp9, vp9_rtx, vp8_answerer,
+                                       vp8_answerer_rtx};
+
+  f1_.set_video_codecs(f1_codecs, f1_codecs);
+  f2_.set_video_codecs(f2_codecs, f2_codecs);
+  std::vector<AudioCodec> audio_codecs;
+  f1_.set_audio_codecs(audio_codecs, audio_codecs);
+  f2_.set_audio_codecs(audio_codecs, audio_codecs);
+
+  // Offer will be {VP8, RTX for VP8}. Answer will be the same.
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+
+  // Updated offer *should* be {VP8, RTX for VP8, VP9, RTX for VP9}.
+  // But if the bug is triggered, RTX for VP8 ends up last.
+  std::unique_ptr<SessionDescription> updated_offer(
+      f2_.CreateOffer(opts, answer.get()));
+
+  const VideoContentDescription* vcd =
+      GetFirstVideoContentDescription(updated_offer.get());
+  std::vector<cricket::VideoCodec> codecs = vcd->codecs();
+  ASSERT_EQ(4u, codecs.size());
+  EXPECT_EQ(vp8_offerer, codecs[0]);
+  EXPECT_EQ(vp8_offerer_rtx, codecs[1]);
+  EXPECT_EQ(vp9, codecs[2]);
+  EXPECT_EQ(vp9_rtx, codecs[3]);
+}
+
+// Create an updated offer that adds video after creating an audio only answer
+// to the original offer. This test verifies that if a video codec and the RTX
+// codec have the same default payload type as an audio codec that is already in
+// use, the added codecs payload types are changed.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       RespondentCreatesOfferWithVideoAndRtxAfterCreatingAudioAnswer) {
+  std::vector<VideoCodec> f1_codecs = MAKE_VECTOR(kVideoCodecs1);
+  // This creates rtx for H264 with the payload type `f1_` uses.
+  AddRtxCodec(VideoCodec::CreateRtxCodec(126, kVideoCodecs1[1].id), &f1_codecs);
+  f1_.set_video_codecs(f1_codecs, f1_codecs);
+
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &opts);
+
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+
+  const AudioContentDescription* acd =
+      GetFirstAudioContentDescription(answer.get());
+  EXPECT_THAT(acd->codecs(), ElementsAreArray(kAudioCodecsAnswer));
+
+  // Now - let `f2_` add video with RTX and let the payload type the RTX codec
+  // reference  be the same as an audio codec that was negotiated in the
+  // first offer/answer exchange.
+  opts.media_description_options.clear();
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+
+  std::vector<VideoCodec> f2_codecs = MAKE_VECTOR(kVideoCodecs2);
+  int used_pl_type = acd->codecs()[0].id;
+  f2_codecs[0].id = used_pl_type;  // Set the payload type for H264.
+  AddRtxCodec(VideoCodec::CreateRtxCodec(125, used_pl_type), &f2_codecs);
+  f2_.set_video_codecs(f2_codecs, f2_codecs);
+
+  std::unique_ptr<SessionDescription> updated_offer(
+      f2_.CreateOffer(opts, answer.get()));
+  ASSERT_TRUE(updated_offer);
+  std::unique_ptr<SessionDescription> updated_answer(
+      f1_.CreateAnswer(updated_offer.get(), opts, answer.get()));
+
+  const AudioContentDescription* updated_acd =
+      GetFirstAudioContentDescription(answer.get());
+  EXPECT_THAT(updated_acd->codecs(), ElementsAreArray(kAudioCodecsAnswer));
+
+  const VideoContentDescription* updated_vcd =
+      GetFirstVideoContentDescription(updated_answer.get());
+
+  ASSERT_EQ("H264", updated_vcd->codecs()[0].name);
+  ASSERT_EQ(cricket::kRtxCodecName, updated_vcd->codecs()[1].name);
+  int new_h264_pl_type = updated_vcd->codecs()[0].id;
+  EXPECT_NE(used_pl_type, new_h264_pl_type);
+  VideoCodec rtx = updated_vcd->codecs()[1];
+  int pt_referenced_by_rtx = rtc::FromString<int>(
+      rtx.params[cricket::kCodecParamAssociatedPayloadType]);
+  EXPECT_EQ(new_h264_pl_type, pt_referenced_by_rtx);
+}
+
+// Create an updated offer with RTX after creating an answer to an offer
+// without RTX, and with different default payload types.
+// Verify that the added RTX codec references the correct payload type.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       RespondentCreatesOfferWithRtxAfterCreatingAnswerWithoutRtx) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+
+  std::vector<VideoCodec> f2_codecs = MAKE_VECTOR(kVideoCodecs2);
+  // This creates rtx for H264 with the payload type `f2_` uses.
+  AddRtxCodec(VideoCodec::CreateRtxCodec(125, kVideoCodecs2[0].id), &f2_codecs);
+  f2_.set_video_codecs(f2_codecs, f2_codecs);
+
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  ASSERT_TRUE(offer.get() != nullptr);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+
+  const VideoContentDescription* vcd =
+      GetFirstVideoContentDescription(answer.get());
+
+  std::vector<VideoCodec> expected_codecs = MAKE_VECTOR(kVideoCodecsAnswer);
+  EXPECT_EQ(expected_codecs, vcd->codecs());
+
+  // Now, ensure that the RTX codec is created correctly when `f2_` creates an
+  // updated offer, even though the default payload types are different from
+  // those of `f1_`.
+  std::unique_ptr<SessionDescription> updated_offer(
+      f2_.CreateOffer(opts, answer.get()));
+  ASSERT_TRUE(updated_offer);
+
+  const VideoContentDescription* updated_vcd =
+      GetFirstVideoContentDescription(updated_offer.get());
+
+  // New offer should attempt to add H263, and RTX for H264.
+  expected_codecs.push_back(kVideoCodecs2[1]);
+  AddRtxCodec(VideoCodec::CreateRtxCodec(125, kVideoCodecs1[1].id),
+              &expected_codecs);
+  EXPECT_EQ(expected_codecs, updated_vcd->codecs());
+}
+
+// Test that RTX is ignored when there is no associated payload type parameter.
+TEST_F(MediaSessionDescriptionFactoryTest, RtxWithoutApt) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &opts);
+  std::vector<VideoCodec> f1_codecs = MAKE_VECTOR(kVideoCodecs1);
+  // This creates RTX without associated payload type parameter.
+  AddRtxCodec(VideoCodec(126, cricket::kRtxCodecName), &f1_codecs);
+  f1_.set_video_codecs(f1_codecs, f1_codecs);
+
+  std::vector<VideoCodec> f2_codecs = MAKE_VECTOR(kVideoCodecs2);
+  // This creates RTX for H264 with the payload type `f2_` uses.
+  AddRtxCodec(VideoCodec::CreateRtxCodec(125, kVideoCodecs2[0].id), &f2_codecs);
+  f2_.set_video_codecs(f2_codecs, f2_codecs);
+
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  // kCodecParamAssociatedPayloadType will always be added to the offer when RTX
+  // is selected. Manually remove kCodecParamAssociatedPayloadType so that it
+  // is possible to test that that RTX is dropped when
+  // kCodecParamAssociatedPayloadType is missing in the offer.
+  MediaContentDescription* media_desc =
+      offer->GetContentDescriptionByName(cricket::CN_VIDEO);
+  ASSERT_TRUE(media_desc);
+  VideoContentDescription* desc = media_desc->as_video();
+  std::vector<VideoCodec> codecs = desc->codecs();
+  for (VideoCodec& codec : codecs) {
+    if (absl::StartsWith(codec.name, cricket::kRtxCodecName)) {
+      codec.params.clear();
+    }
+  }
+  desc->set_codecs(codecs);
+
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+
+  EXPECT_THAT(
+      GetCodecNames(GetFirstVideoContentDescription(answer.get())->codecs()),
+      Not(Contains(cricket::kRtxCodecName)));
+}
+
+// Test that RTX will be filtered out in the answer if its associated payload
+// type doesn't match the local value.
+TEST_F(MediaSessionDescriptionFactoryTest, FilterOutRtxIfAptDoesntMatch) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &opts);
+  std::vector<VideoCodec> f1_codecs = MAKE_VECTOR(kVideoCodecs1);
+  // This creates RTX for H264 in sender.
+  AddRtxCodec(VideoCodec::CreateRtxCodec(126, kVideoCodecs1[1].id), &f1_codecs);
+  f1_.set_video_codecs(f1_codecs, f1_codecs);
+
+  std::vector<VideoCodec> f2_codecs = MAKE_VECTOR(kVideoCodecs2);
+  // This creates RTX for H263 in receiver.
+  AddRtxCodec(VideoCodec::CreateRtxCodec(125, kVideoCodecs2[1].id), &f2_codecs);
+  f2_.set_video_codecs(f2_codecs, f2_codecs);
+
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  // Associated payload type doesn't match, therefore, RTX codec is removed in
+  // the answer.
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+
+  EXPECT_THAT(
+      GetCodecNames(GetFirstVideoContentDescription(answer.get())->codecs()),
+      Not(Contains(cricket::kRtxCodecName)));
+}
+
+// Test that when multiple RTX codecs are offered, only the matched RTX codec
+// is added in the answer, and the unsupported RTX codec is filtered out.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       FilterOutUnsupportedRtxWhenCreatingAnswer) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &opts);
+  std::vector<VideoCodec> f1_codecs = MAKE_VECTOR(kVideoCodecs1);
+  // This creates RTX for H264-SVC in sender.
+  AddRtxCodec(VideoCodec::CreateRtxCodec(125, kVideoCodecs1[0].id), &f1_codecs);
+  f1_.set_video_codecs(f1_codecs, f1_codecs);
+
+  // This creates RTX for H264 in sender.
+  AddRtxCodec(VideoCodec::CreateRtxCodec(126, kVideoCodecs1[1].id), &f1_codecs);
+  f1_.set_video_codecs(f1_codecs, f1_codecs);
+
+  std::vector<VideoCodec> f2_codecs = MAKE_VECTOR(kVideoCodecs2);
+  // This creates RTX for H264 in receiver.
+  AddRtxCodec(VideoCodec::CreateRtxCodec(124, kVideoCodecs2[0].id), &f2_codecs);
+  f2_.set_video_codecs(f2_codecs, f1_codecs);
+
+  // H264-SVC codec is removed in the answer, therefore, associated RTX codec
+  // for H264-SVC should also be removed.
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+  const VideoContentDescription* vcd =
+      GetFirstVideoContentDescription(answer.get());
+  std::vector<VideoCodec> expected_codecs = MAKE_VECTOR(kVideoCodecsAnswer);
+  AddRtxCodec(VideoCodec::CreateRtxCodec(126, kVideoCodecs1[1].id),
+              &expected_codecs);
+
+  EXPECT_EQ(expected_codecs, vcd->codecs());
+}
+
+// Test that after one RTX codec has been negotiated, a new offer can attempt
+// to add another.
+TEST_F(MediaSessionDescriptionFactoryTest, AddSecondRtxInNewOffer) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &opts);
+  std::vector<VideoCodec> f1_codecs = MAKE_VECTOR(kVideoCodecs1);
+  // This creates RTX for H264 for the offerer.
+  AddRtxCodec(VideoCodec::CreateRtxCodec(126, kVideoCodecs1[1].id), &f1_codecs);
+  f1_.set_video_codecs(f1_codecs, f1_codecs);
+
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  ASSERT_TRUE(offer);
+  const VideoContentDescription* vcd =
+      GetFirstVideoContentDescription(offer.get());
+
+  std::vector<VideoCodec> expected_codecs = MAKE_VECTOR(kVideoCodecs1);
+  AddRtxCodec(VideoCodec::CreateRtxCodec(126, kVideoCodecs1[1].id),
+              &expected_codecs);
+  EXPECT_EQ(expected_codecs, vcd->codecs());
+
+  // Now, attempt to add RTX for H264-SVC.
+  AddRtxCodec(VideoCodec::CreateRtxCodec(125, kVideoCodecs1[0].id), &f1_codecs);
+  f1_.set_video_codecs(f1_codecs, f1_codecs);
+
+  std::unique_ptr<SessionDescription> updated_offer(
+      f1_.CreateOffer(opts, offer.get()));
+  ASSERT_TRUE(updated_offer);
+  vcd = GetFirstVideoContentDescription(updated_offer.get());
+
+  AddRtxCodec(VideoCodec::CreateRtxCodec(125, kVideoCodecs1[0].id),
+              &expected_codecs);
+  EXPECT_EQ(expected_codecs, vcd->codecs());
+}
+
+// Test that when RTX is used in conjunction with simulcast, an RTX ssrc is
+// generated for each simulcast ssrc and correctly grouped.
+TEST_F(MediaSessionDescriptionFactoryTest, SimSsrcsGenerateMultipleRtxSsrcs) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  // Add simulcast streams.
+  AttachSenderToMediaDescriptionOptions("video", MEDIA_TYPE_VIDEO, "stream1",
+                                        {"stream1label"}, 3, &opts);
+
+  // Use a single real codec, and then add RTX for it.
+  std::vector<VideoCodec> f1_codecs;
+  f1_codecs.push_back(VideoCodec(97, "H264"));
+  AddRtxCodec(VideoCodec::CreateRtxCodec(125, 97), &f1_codecs);
+  f1_.set_video_codecs(f1_codecs, f1_codecs);
+
+  // Ensure that the offer has an RTX ssrc for each regular ssrc, and that there
+  // is a FID ssrc + grouping for each.
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  MediaContentDescription* media_desc =
+      offer->GetContentDescriptionByName(cricket::CN_VIDEO);
+  ASSERT_TRUE(media_desc);
+  VideoContentDescription* desc = media_desc->as_video();
+  const StreamParamsVec& streams = desc->streams();
+  // Single stream.
+  ASSERT_EQ(1u, streams.size());
+  // Stream should have 6 ssrcs: 3 for video, 3 for RTX.
+  EXPECT_EQ(6u, streams[0].ssrcs.size());
+  // And should have a SIM group for the simulcast.
+  EXPECT_TRUE(streams[0].has_ssrc_group("SIM"));
+  // And a FID group for RTX.
+  EXPECT_TRUE(streams[0].has_ssrc_group("FID"));
+  std::vector<uint32_t> primary_ssrcs;
+  streams[0].GetPrimarySsrcs(&primary_ssrcs);
+  EXPECT_EQ(3u, primary_ssrcs.size());
+  std::vector<uint32_t> fid_ssrcs;
+  streams[0].GetFidSsrcs(primary_ssrcs, &fid_ssrcs);
+  EXPECT_EQ(3u, fid_ssrcs.size());
+}
+
+// Test that, when the FlexFEC codec is added, a FlexFEC ssrc is created
+// together with a FEC-FR grouping. Guarded by WebRTC-FlexFEC-03 trial.
+TEST_F(MediaSessionDescriptionFactoryTest, GenerateFlexfecSsrc) {
+  webrtc::test::ScopedKeyValueConfig override_field_trials(
+      field_trials, "WebRTC-FlexFEC-03/Enabled/");
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  // Add single stream.
+  AttachSenderToMediaDescriptionOptions("video", MEDIA_TYPE_VIDEO, "stream1",
+                                        {"stream1label"}, 1, &opts);
+
+  // Use a single real codec, and then add FlexFEC for it.
+  std::vector<VideoCodec> f1_codecs;
+  f1_codecs.push_back(VideoCodec(97, "H264"));
+  f1_codecs.push_back(VideoCodec(118, "flexfec-03"));
+  f1_.set_video_codecs(f1_codecs, f1_codecs);
+
+  // Ensure that the offer has a single FlexFEC ssrc and that
+  // there is no FEC-FR ssrc + grouping for each.
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  ASSERT_TRUE(offer.get() != nullptr);
+  MediaContentDescription* media_desc =
+      offer->GetContentDescriptionByName(cricket::CN_VIDEO);
+  ASSERT_TRUE(media_desc);
+  VideoContentDescription* desc = media_desc->as_video();
+  const StreamParamsVec& streams = desc->streams();
+  // Single stream.
+  ASSERT_EQ(1u, streams.size());
+  // Stream should have 2 ssrcs: 1 for video, 1 for FlexFEC.
+  EXPECT_EQ(2u, streams[0].ssrcs.size());
+  // And should have a FEC-FR group for FlexFEC.
+  EXPECT_TRUE(streams[0].has_ssrc_group("FEC-FR"));
+  std::vector<uint32_t> primary_ssrcs;
+  streams[0].GetPrimarySsrcs(&primary_ssrcs);
+  ASSERT_EQ(1u, primary_ssrcs.size());
+  uint32_t flexfec_ssrc;
+  EXPECT_TRUE(streams[0].GetFecFrSsrc(primary_ssrcs[0], &flexfec_ssrc));
+  EXPECT_NE(flexfec_ssrc, 0u);
+}
+
+// Test that FlexFEC is disabled for simulcast.
+// TODO(brandtr): Remove this test when we support simulcast, either through
+// multiple FlexfecSenders, or through multistream protection.
+TEST_F(MediaSessionDescriptionFactoryTest, SimSsrcsGenerateNoFlexfecSsrcs) {
+  webrtc::test::ScopedKeyValueConfig override_field_trials(
+      field_trials, "WebRTC-FlexFEC-03/Enabled/");
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  // Add simulcast streams.
+  AttachSenderToMediaDescriptionOptions("video", MEDIA_TYPE_VIDEO, "stream1",
+                                        {"stream1label"}, 3, &opts);
+
+  // Use a single real codec, and then add FlexFEC for it.
+  std::vector<VideoCodec> f1_codecs;
+  f1_codecs.push_back(VideoCodec(97, "H264"));
+  f1_codecs.push_back(VideoCodec(118, "flexfec-03"));
+  f1_.set_video_codecs(f1_codecs, f1_codecs);
+
+  // Ensure that the offer has no FlexFEC ssrcs for each regular ssrc, and that
+  // there is no FEC-FR ssrc + grouping for each.
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  ASSERT_TRUE(offer.get() != nullptr);
+  MediaContentDescription* media_desc =
+      offer->GetContentDescriptionByName(cricket::CN_VIDEO);
+  ASSERT_TRUE(media_desc);
+  VideoContentDescription* desc = media_desc->as_video();
+  const StreamParamsVec& streams = desc->streams();
+  // Single stream.
+  ASSERT_EQ(1u, streams.size());
+  // Stream should have 3 ssrcs: 3 for video, 0 for FlexFEC.
+  EXPECT_EQ(3u, streams[0].ssrcs.size());
+  // And should have a SIM group for the simulcast.
+  EXPECT_TRUE(streams[0].has_ssrc_group("SIM"));
+  // And not a FEC-FR group for FlexFEC.
+  EXPECT_FALSE(streams[0].has_ssrc_group("FEC-FR"));
+  std::vector<uint32_t> primary_ssrcs;
+  streams[0].GetPrimarySsrcs(&primary_ssrcs);
+  EXPECT_EQ(3u, primary_ssrcs.size());
+  for (uint32_t primary_ssrc : primary_ssrcs) {
+    uint32_t flexfec_ssrc;
+    EXPECT_FALSE(streams[0].GetFecFrSsrc(primary_ssrc, &flexfec_ssrc));
+  }
+}
+
+// Create an updated offer after creating an answer to the original offer and
+// verify that the RTP header extensions that were part of the original answer
+// are not changed in the updated offer.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       RespondentCreatesOfferAfterCreatingAnswerWithRtpExtensions) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+
+  SetAudioVideoRtpHeaderExtensions(MAKE_VECTOR(kAudioRtpExtension1),
+                                   MAKE_VECTOR(kVideoRtpExtension1), &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+  SetAudioVideoRtpHeaderExtensions(MAKE_VECTOR(kAudioRtpExtension2),
+                                   MAKE_VECTOR(kVideoRtpExtension2), &opts);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, NULL);
+
+  EXPECT_EQ(
+      MAKE_VECTOR(kAudioRtpExtensionAnswer),
+      GetFirstAudioContentDescription(answer.get())->rtp_header_extensions());
+  EXPECT_EQ(
+      MAKE_VECTOR(kVideoRtpExtensionAnswer),
+      GetFirstVideoContentDescription(answer.get())->rtp_header_extensions());
+
+  std::unique_ptr<SessionDescription> updated_offer(
+      f2_.CreateOffer(opts, answer.get()));
+
+  // The expected RTP header extensions in the new offer are the resulting
+  // extensions from the first offer/answer exchange plus the extensions only
+  // `f2_` offer.
+  // Since the default local extension id `f2_` uses has already been used by
+  // `f1_` for another extensions, it is changed to 13.
+  const RtpExtension kUpdatedAudioRtpExtensions[] = {
+      kAudioRtpExtensionAnswer[0],
+      RtpExtension(kAudioRtpExtension2[1].uri, 13),
+      kAudioRtpExtension2[2],
+  };
+
+  // Since the default local extension id `f2_` uses has already been used by
+  // `f1_` for another extensions, is is changed to 12.
+  const RtpExtension kUpdatedVideoRtpExtensions[] = {
+      kVideoRtpExtensionAnswer[0],
+      RtpExtension(kVideoRtpExtension2[1].uri, 12),
+      kVideoRtpExtension2[2],
+  };
+
+  const AudioContentDescription* updated_acd =
+      GetFirstAudioContentDescription(updated_offer.get());
+  EXPECT_EQ(MAKE_VECTOR(kUpdatedAudioRtpExtensions),
+            updated_acd->rtp_header_extensions());
+
+  const VideoContentDescription* updated_vcd =
+      GetFirstVideoContentDescription(updated_offer.get());
+  EXPECT_EQ(MAKE_VECTOR(kUpdatedVideoRtpExtensions),
+            updated_vcd->rtp_header_extensions());
+}
+
+// Verify that if the same RTP extension URI is used for audio and video, the
+// same ID is used. Also verify that the ID isn't changed when creating an
+// updated offer (this was previously a bug).
+TEST_F(MediaSessionDescriptionFactoryTest, RtpExtensionIdReused) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+
+  SetAudioVideoRtpHeaderExtensions(MAKE_VECTOR(kAudioRtpExtension3),
+                                   MAKE_VECTOR(kVideoRtpExtension3), &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+
+  // Since the audio extensions used ID 3 for "both_audio_and_video", so should
+  // the video extensions.
+  const RtpExtension kExpectedVideoRtpExtension[] = {
+      kVideoRtpExtension3[0],
+      kAudioRtpExtension3[1],
+  };
+
+  EXPECT_EQ(
+      MAKE_VECTOR(kAudioRtpExtension3),
+      GetFirstAudioContentDescription(offer.get())->rtp_header_extensions());
+  EXPECT_EQ(
+      MAKE_VECTOR(kExpectedVideoRtpExtension),
+      GetFirstVideoContentDescription(offer.get())->rtp_header_extensions());
+
+  // Nothing should change when creating a new offer
+  std::unique_ptr<SessionDescription> updated_offer(
+      f1_.CreateOffer(opts, offer.get()));
+
+  EXPECT_EQ(MAKE_VECTOR(kAudioRtpExtension3),
+            GetFirstAudioContentDescription(updated_offer.get())
+                ->rtp_header_extensions());
+  EXPECT_EQ(MAKE_VECTOR(kExpectedVideoRtpExtension),
+            GetFirstVideoContentDescription(updated_offer.get())
+                ->rtp_header_extensions());
+}
+
+// Same as "RtpExtensionIdReused" above for encrypted RTP extensions.
+TEST_F(MediaSessionDescriptionFactoryTest, RtpExtensionIdReusedEncrypted) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+
+  f1_.set_enable_encrypted_rtp_header_extensions(true);
+  f2_.set_enable_encrypted_rtp_header_extensions(true);
+
+  SetAudioVideoRtpHeaderExtensions(
+      MAKE_VECTOR(kAudioRtpExtension3ForEncryption),
+      MAKE_VECTOR(kVideoRtpExtension3ForEncryption), &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, NULL);
+
+  EXPECT_EQ(
+      MAKE_VECTOR(kAudioRtpExtension3ForEncryptionOffer),
+      GetFirstAudioContentDescription(offer.get())->rtp_header_extensions());
+  EXPECT_EQ(
+      MAKE_VECTOR(kVideoRtpExtension3ForEncryptionOffer),
+      GetFirstVideoContentDescription(offer.get())->rtp_header_extensions());
+
+  // Nothing should change when creating a new offer
+  std::unique_ptr<SessionDescription> updated_offer(
+      f1_.CreateOffer(opts, offer.get()));
+
+  EXPECT_EQ(MAKE_VECTOR(kAudioRtpExtension3ForEncryptionOffer),
+            GetFirstAudioContentDescription(updated_offer.get())
+                ->rtp_header_extensions());
+  EXPECT_EQ(MAKE_VECTOR(kVideoRtpExtension3ForEncryptionOffer),
+            GetFirstVideoContentDescription(updated_offer.get())
+                ->rtp_header_extensions());
+}
+
+TEST(MediaSessionDescription, CopySessionDescription) {
+  SessionDescription source;
+  cricket::ContentGroup group(cricket::CN_AUDIO);
+  source.AddGroup(group);
+  std::unique_ptr<AudioContentDescription> acd =
+      std::make_unique<AudioContentDescription>();
+  acd->set_codecs(MAKE_VECTOR(kAudioCodecs1));
+  acd->AddLegacyStream(1);
+  source.AddContent(cricket::CN_AUDIO, MediaProtocolType::kRtp, acd->Clone());
+  std::unique_ptr<VideoContentDescription> vcd =
+      std::make_unique<VideoContentDescription>();
+  vcd->set_codecs(MAKE_VECTOR(kVideoCodecs1));
+  vcd->AddLegacyStream(2);
+  source.AddContent(cricket::CN_VIDEO, MediaProtocolType::kRtp, vcd->Clone());
+
+  std::unique_ptr<SessionDescription> copy = source.Clone();
+  ASSERT_TRUE(copy.get() != NULL);
+  EXPECT_TRUE(copy->HasGroup(cricket::CN_AUDIO));
+  const ContentInfo* ac = copy->GetContentByName("audio");
+  const ContentInfo* vc = copy->GetContentByName("video");
+  ASSERT_TRUE(ac != NULL);
+  ASSERT_TRUE(vc != NULL);
+  EXPECT_EQ(MediaProtocolType::kRtp, ac->type);
+  const AudioContentDescription* acd_copy = ac->media_description()->as_audio();
+  EXPECT_EQ(acd->codecs(), acd_copy->codecs());
+  EXPECT_EQ(1u, acd->first_ssrc());
+
+  EXPECT_EQ(MediaProtocolType::kRtp, vc->type);
+  const VideoContentDescription* vcd_copy = vc->media_description()->as_video();
+  EXPECT_EQ(vcd->codecs(), vcd_copy->codecs());
+  EXPECT_EQ(2u, vcd->first_ssrc());
+}
+
+// The below TestTransportInfoXXX tests create different offers/answers, and
+// ensure the TransportInfo in the SessionDescription matches what we expect.
+TEST_F(MediaSessionDescriptionFactoryTest, TestTransportInfoOfferAudio) {
+  MediaSessionOptions options;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &options);
+  TestTransportInfo(true, options, false);
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestTransportInfoOfferIceRenomination) {
+  MediaSessionOptions options;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &options);
+  options.media_description_options[0]
+      .transport_options.enable_ice_renomination = true;
+  TestTransportInfo(true, options, false);
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest, TestTransportInfoOfferAudioCurrent) {
+  MediaSessionOptions options;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &options);
+  TestTransportInfo(true, options, true);
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest, TestTransportInfoOfferMultimedia) {
+  MediaSessionOptions options;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &options);
+  TestTransportInfo(true, options, false);
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestTransportInfoOfferMultimediaCurrent) {
+  MediaSessionOptions options;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &options);
+  TestTransportInfo(true, options, true);
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest, TestTransportInfoOfferBundle) {
+  MediaSessionOptions options;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &options);
+  options.bundle_enabled = true;
+  TestTransportInfo(true, options, false);
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestTransportInfoOfferBundleCurrent) {
+  MediaSessionOptions options;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &options);
+  options.bundle_enabled = true;
+  TestTransportInfo(true, options, true);
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest, TestTransportInfoAnswerAudio) {
+  MediaSessionOptions options;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &options);
+  TestTransportInfo(false, options, false);
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestTransportInfoAnswerIceRenomination) {
+  MediaSessionOptions options;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &options);
+  options.media_description_options[0]
+      .transport_options.enable_ice_renomination = true;
+  TestTransportInfo(false, options, false);
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestTransportInfoAnswerAudioCurrent) {
+  MediaSessionOptions options;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &options);
+  TestTransportInfo(false, options, true);
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest, TestTransportInfoAnswerMultimedia) {
+  MediaSessionOptions options;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &options);
+  TestTransportInfo(false, options, false);
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestTransportInfoAnswerMultimediaCurrent) {
+  MediaSessionOptions options;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &options);
+  TestTransportInfo(false, options, true);
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest, TestTransportInfoAnswerBundle) {
+  MediaSessionOptions options;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &options);
+  options.bundle_enabled = true;
+  TestTransportInfo(false, options, false);
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestTransportInfoAnswerBundleCurrent) {
+  MediaSessionOptions options;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &options);
+  options.bundle_enabled = true;
+  TestTransportInfo(false, options, true);
+}
+
+// Create an offer with bundle enabled and verify the crypto parameters are
+// the common set of the available cryptos.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCryptoWithOfferBundle) {
+  TestCryptoWithBundle(true);
+}
+
+// Create an answer with bundle enabled and verify the crypto parameters are
+// the common set of the available cryptos.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCryptoWithAnswerBundle) {
+  TestCryptoWithBundle(false);
+}
+
+// Verifies that creating answer fails if the offer has UDP/TLS/RTP/SAVPF but
+// DTLS is not enabled locally.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       TestOfferDtlsSavpfWithoutDtlsFailed) {
+  f1_.set_secure(SEC_ENABLED);
+  f2_.set_secure(SEC_ENABLED);
+  tdf1_.set_secure(SEC_DISABLED);
+  tdf2_.set_secure(SEC_DISABLED);
+
+  std::unique_ptr<SessionDescription> offer =
+      f1_.CreateOffer(CreatePlanBMediaSessionOptions(), NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  ContentInfo* offer_content = offer->GetContentByName("audio");
+  ASSERT_TRUE(offer_content != NULL);
+  AudioContentDescription* offer_audio_desc =
+      offer_content->media_description()->as_audio();
+  offer_audio_desc->set_protocol(cricket::kMediaProtocolDtlsSavpf);
+
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), CreatePlanBMediaSessionOptions(), NULL);
+  ASSERT_TRUE(answer != NULL);
+  ContentInfo* answer_content = answer->GetContentByName("audio");
+  ASSERT_TRUE(answer_content != NULL);
+
+  ASSERT_TRUE(answer_content->rejected);
+}
+
+// Offers UDP/TLS/RTP/SAVPF and verifies the answer can be created and contains
+// UDP/TLS/RTP/SAVPF.
+TEST_F(MediaSessionDescriptionFactoryTest, TestOfferDtlsSavpfCreateAnswer) {
+  f1_.set_secure(SEC_ENABLED);
+  f2_.set_secure(SEC_ENABLED);
+  tdf1_.set_secure(SEC_ENABLED);
+  tdf2_.set_secure(SEC_ENABLED);
+
+  std::unique_ptr<SessionDescription> offer =
+      f1_.CreateOffer(CreatePlanBMediaSessionOptions(), NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  ContentInfo* offer_content = offer->GetContentByName("audio");
+  ASSERT_TRUE(offer_content != NULL);
+  AudioContentDescription* offer_audio_desc =
+      offer_content->media_description()->as_audio();
+  offer_audio_desc->set_protocol(cricket::kMediaProtocolDtlsSavpf);
+
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), CreatePlanBMediaSessionOptions(), NULL);
+  ASSERT_TRUE(answer != NULL);
+
+  const ContentInfo* answer_content = answer->GetContentByName("audio");
+  ASSERT_TRUE(answer_content != NULL);
+  ASSERT_FALSE(answer_content->rejected);
+
+  const AudioContentDescription* answer_audio_desc =
+      answer_content->media_description()->as_audio();
+  EXPECT_EQ(cricket::kMediaProtocolDtlsSavpf, answer_audio_desc->protocol());
+}
+
+// Test that we include both SDES and DTLS in the offer, but only include SDES
+// in the answer if DTLS isn't negotiated.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCryptoDtls) {
+  f1_.set_secure(SEC_ENABLED);
+  f2_.set_secure(SEC_ENABLED);
+  tdf1_.set_secure(SEC_ENABLED);
+  tdf2_.set_secure(SEC_DISABLED);
+  MediaSessionOptions options;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &options);
+  std::unique_ptr<SessionDescription> offer, answer;
+  const cricket::MediaContentDescription* audio_media_desc;
+  const cricket::MediaContentDescription* video_media_desc;
+  const cricket::TransportDescription* audio_trans_desc;
+  const cricket::TransportDescription* video_trans_desc;
+
+  // Generate an offer with SDES and DTLS support.
+  offer = f1_.CreateOffer(options, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+
+  audio_media_desc = offer->GetContentDescriptionByName("audio");
+  ASSERT_TRUE(audio_media_desc != NULL);
+  video_media_desc = offer->GetContentDescriptionByName("video");
+  ASSERT_TRUE(video_media_desc != NULL);
+  EXPECT_EQ(1u, audio_media_desc->cryptos().size());
+  EXPECT_EQ(1u, video_media_desc->cryptos().size());
+
+  audio_trans_desc = offer->GetTransportDescriptionByName("audio");
+  ASSERT_TRUE(audio_trans_desc != NULL);
+  video_trans_desc = offer->GetTransportDescriptionByName("video");
+  ASSERT_TRUE(video_trans_desc != NULL);
+  ASSERT_TRUE(audio_trans_desc->identity_fingerprint.get() != NULL);
+  ASSERT_TRUE(video_trans_desc->identity_fingerprint.get() != NULL);
+
+  // Generate an answer with only SDES support, since tdf2 has crypto disabled.
+  answer = f2_.CreateAnswer(offer.get(), options, NULL);
+  ASSERT_TRUE(answer.get() != NULL);
+
+  audio_media_desc = answer->GetContentDescriptionByName("audio");
+  ASSERT_TRUE(audio_media_desc != NULL);
+  video_media_desc = answer->GetContentDescriptionByName("video");
+  ASSERT_TRUE(video_media_desc != NULL);
+  EXPECT_EQ(1u, audio_media_desc->cryptos().size());
+  EXPECT_EQ(1u, video_media_desc->cryptos().size());
+
+  audio_trans_desc = answer->GetTransportDescriptionByName("audio");
+  ASSERT_TRUE(audio_trans_desc != NULL);
+  video_trans_desc = answer->GetTransportDescriptionByName("video");
+  ASSERT_TRUE(video_trans_desc != NULL);
+  ASSERT_TRUE(audio_trans_desc->identity_fingerprint.get() == NULL);
+  ASSERT_TRUE(video_trans_desc->identity_fingerprint.get() == NULL);
+
+  // Enable DTLS; the answer should now only have DTLS support.
+  tdf2_.set_secure(SEC_ENABLED);
+  answer = f2_.CreateAnswer(offer.get(), options, NULL);
+  ASSERT_TRUE(answer.get() != NULL);
+
+  audio_media_desc = answer->GetContentDescriptionByName("audio");
+  ASSERT_TRUE(audio_media_desc != NULL);
+  video_media_desc = answer->GetContentDescriptionByName("video");
+  ASSERT_TRUE(video_media_desc != NULL);
+  EXPECT_TRUE(audio_media_desc->cryptos().empty());
+  EXPECT_TRUE(video_media_desc->cryptos().empty());
+  EXPECT_EQ(cricket::kMediaProtocolSavpf, audio_media_desc->protocol());
+  EXPECT_EQ(cricket::kMediaProtocolSavpf, video_media_desc->protocol());
+
+  audio_trans_desc = answer->GetTransportDescriptionByName("audio");
+  ASSERT_TRUE(audio_trans_desc != NULL);
+  video_trans_desc = answer->GetTransportDescriptionByName("video");
+  ASSERT_TRUE(video_trans_desc != NULL);
+  ASSERT_TRUE(audio_trans_desc->identity_fingerprint.get() != NULL);
+  ASSERT_TRUE(video_trans_desc->identity_fingerprint.get() != NULL);
+
+  // Try creating offer again. DTLS enabled now, crypto's should be empty
+  // in new offer.
+  offer = f1_.CreateOffer(options, offer.get());
+  ASSERT_TRUE(offer.get() != NULL);
+  audio_media_desc = offer->GetContentDescriptionByName("audio");
+  ASSERT_TRUE(audio_media_desc != NULL);
+  video_media_desc = offer->GetContentDescriptionByName("video");
+  ASSERT_TRUE(video_media_desc != NULL);
+  EXPECT_TRUE(audio_media_desc->cryptos().empty());
+  EXPECT_TRUE(video_media_desc->cryptos().empty());
+
+  audio_trans_desc = offer->GetTransportDescriptionByName("audio");
+  ASSERT_TRUE(audio_trans_desc != NULL);
+  video_trans_desc = offer->GetTransportDescriptionByName("video");
+  ASSERT_TRUE(video_trans_desc != NULL);
+  ASSERT_TRUE(audio_trans_desc->identity_fingerprint.get() != NULL);
+  ASSERT_TRUE(video_trans_desc->identity_fingerprint.get() != NULL);
+}
+
+// Test that an answer can't be created if cryptos are required but the offer is
+// unsecure.
+TEST_F(MediaSessionDescriptionFactoryTest, TestSecureAnswerToUnsecureOffer) {
+  MediaSessionOptions options = CreatePlanBMediaSessionOptions();
+  f1_.set_secure(SEC_DISABLED);
+  tdf1_.set_secure(SEC_DISABLED);
+  f2_.set_secure(SEC_REQUIRED);
+  tdf1_.set_secure(SEC_ENABLED);
+
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(options, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), options, NULL);
+  EXPECT_TRUE(answer.get() == NULL);
+}
+
+// Test that we accept a DTLS offer without SDES and create an appropriate
+// answer.
+TEST_F(MediaSessionDescriptionFactoryTest, TestCryptoOfferDtlsButNotSdes) {
+  f1_.set_secure(SEC_DISABLED);
+  f2_.set_secure(SEC_ENABLED);
+  tdf1_.set_secure(SEC_ENABLED);
+  tdf2_.set_secure(SEC_ENABLED);
+  MediaSessionOptions options;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &options);
+
+  // Generate an offer with DTLS but without SDES.
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(options, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+
+  const AudioContentDescription* audio_offer =
+      GetFirstAudioContentDescription(offer.get());
+  ASSERT_TRUE(audio_offer->cryptos().empty());
+  const VideoContentDescription* video_offer =
+      GetFirstVideoContentDescription(offer.get());
+  ASSERT_TRUE(video_offer->cryptos().empty());
+
+  const cricket::TransportDescription* audio_offer_trans_desc =
+      offer->GetTransportDescriptionByName("audio");
+  ASSERT_TRUE(audio_offer_trans_desc->identity_fingerprint.get() != NULL);
+  const cricket::TransportDescription* video_offer_trans_desc =
+      offer->GetTransportDescriptionByName("video");
+  ASSERT_TRUE(video_offer_trans_desc->identity_fingerprint.get() != NULL);
+
+  // Generate an answer with DTLS.
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), options, NULL);
+  ASSERT_TRUE(answer.get() != NULL);
+
+  const cricket::TransportDescription* audio_answer_trans_desc =
+      answer->GetTransportDescriptionByName("audio");
+  EXPECT_TRUE(audio_answer_trans_desc->identity_fingerprint.get() != NULL);
+  const cricket::TransportDescription* video_answer_trans_desc =
+      answer->GetTransportDescriptionByName("video");
+  EXPECT_TRUE(video_answer_trans_desc->identity_fingerprint.get() != NULL);
+}
+
+// Verifies if vad_enabled option is set to false, CN codecs are not present in
+// offer or answer.
+TEST_F(MediaSessionDescriptionFactoryTest, TestVADEnableOption) {
+  MediaSessionOptions options;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &options);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(options, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  const ContentInfo* audio_content = offer->GetContentByName("audio");
+  EXPECT_FALSE(VerifyNoCNCodecs(audio_content));
+
+  options.vad_enabled = false;
+  offer = f1_.CreateOffer(options, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  audio_content = offer->GetContentByName("audio");
+  EXPECT_TRUE(VerifyNoCNCodecs(audio_content));
+  std::unique_ptr<SessionDescription> answer =
+      f1_.CreateAnswer(offer.get(), options, NULL);
+  ASSERT_TRUE(answer.get() != NULL);
+  audio_content = answer->GetContentByName("audio");
+  EXPECT_TRUE(VerifyNoCNCodecs(audio_content));
+}
+
+// Test that the generated MIDs match the existing offer.
+TEST_F(MediaSessionDescriptionFactoryTest, TestMIDsMatchesExistingOffer) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio_modified",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video_modified",
+                             RtpTransceiverDirection::kRecvOnly, kActive,
+                             &opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_DATA, "data_modified",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  // Create offer.
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  std::unique_ptr<SessionDescription> updated_offer(
+      f1_.CreateOffer(opts, offer.get()));
+
+  const ContentInfo* audio_content = GetFirstAudioContent(updated_offer.get());
+  const ContentInfo* video_content = GetFirstVideoContent(updated_offer.get());
+  const ContentInfo* data_content = GetFirstDataContent(updated_offer.get());
+  ASSERT_TRUE(audio_content != nullptr);
+  ASSERT_TRUE(video_content != nullptr);
+  ASSERT_TRUE(data_content != nullptr);
+  EXPECT_EQ("audio_modified", audio_content->name);
+  EXPECT_EQ("video_modified", video_content->name);
+  EXPECT_EQ("data_modified", data_content->name);
+}
+
+// The following tests verify that the unified plan SDP is supported.
+// Test that we can create an offer with multiple media sections of same media
+// type.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       CreateOfferWithMultipleAVMediaSections) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio_1",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  AttachSenderToMediaDescriptionOptions(
+      "audio_1", MEDIA_TYPE_AUDIO, kAudioTrack1, {kMediaStream1}, 1, &opts);
+
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video_1",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  AttachSenderToMediaDescriptionOptions(
+      "video_1", MEDIA_TYPE_VIDEO, kVideoTrack1, {kMediaStream1}, 1, &opts);
+
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio_2",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  AttachSenderToMediaDescriptionOptions(
+      "audio_2", MEDIA_TYPE_AUDIO, kAudioTrack2, {kMediaStream2}, 1, &opts);
+
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video_2",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  AttachSenderToMediaDescriptionOptions(
+      "video_2", MEDIA_TYPE_VIDEO, kVideoTrack2, {kMediaStream2}, 1, &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  ASSERT_TRUE(offer);
+
+  ASSERT_EQ(4u, offer->contents().size());
+  EXPECT_FALSE(offer->contents()[0].rejected);
+  const AudioContentDescription* acd =
+      offer->contents()[0].media_description()->as_audio();
+  ASSERT_EQ(1u, acd->streams().size());
+  EXPECT_EQ(kAudioTrack1, acd->streams()[0].id);
+  EXPECT_EQ(RtpTransceiverDirection::kSendRecv, acd->direction());
+
+  EXPECT_FALSE(offer->contents()[1].rejected);
+  const VideoContentDescription* vcd =
+      offer->contents()[1].media_description()->as_video();
+  ASSERT_EQ(1u, vcd->streams().size());
+  EXPECT_EQ(kVideoTrack1, vcd->streams()[0].id);
+  EXPECT_EQ(RtpTransceiverDirection::kSendRecv, vcd->direction());
+
+  EXPECT_FALSE(offer->contents()[2].rejected);
+  acd = offer->contents()[2].media_description()->as_audio();
+  ASSERT_EQ(1u, acd->streams().size());
+  EXPECT_EQ(kAudioTrack2, acd->streams()[0].id);
+  EXPECT_EQ(RtpTransceiverDirection::kSendRecv, acd->direction());
+
+  EXPECT_FALSE(offer->contents()[3].rejected);
+  vcd = offer->contents()[3].media_description()->as_video();
+  ASSERT_EQ(1u, vcd->streams().size());
+  EXPECT_EQ(kVideoTrack2, vcd->streams()[0].id);
+  EXPECT_EQ(RtpTransceiverDirection::kSendRecv, vcd->direction());
+}
+
+// Test that we can create an answer with multiple media sections of same media
+// type.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       CreateAnswerWithMultipleAVMediaSections) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio_1",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  AttachSenderToMediaDescriptionOptions(
+      "audio_1", MEDIA_TYPE_AUDIO, kAudioTrack1, {kMediaStream1}, 1, &opts);
+
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video_1",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  AttachSenderToMediaDescriptionOptions(
+      "video_1", MEDIA_TYPE_VIDEO, kVideoTrack1, {kMediaStream1}, 1, &opts);
+
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio_2",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  AttachSenderToMediaDescriptionOptions(
+      "audio_2", MEDIA_TYPE_AUDIO, kAudioTrack2, {kMediaStream2}, 1, &opts);
+
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video_2",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  AttachSenderToMediaDescriptionOptions(
+      "video_2", MEDIA_TYPE_VIDEO, kVideoTrack2, {kMediaStream2}, 1, &opts);
+
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  ASSERT_TRUE(offer);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+
+  ASSERT_EQ(4u, answer->contents().size());
+  EXPECT_FALSE(answer->contents()[0].rejected);
+  const AudioContentDescription* acd =
+      answer->contents()[0].media_description()->as_audio();
+  ASSERT_EQ(1u, acd->streams().size());
+  EXPECT_EQ(kAudioTrack1, acd->streams()[0].id);
+  EXPECT_EQ(RtpTransceiverDirection::kSendRecv, acd->direction());
+
+  EXPECT_FALSE(answer->contents()[1].rejected);
+  const VideoContentDescription* vcd =
+      answer->contents()[1].media_description()->as_video();
+  ASSERT_EQ(1u, vcd->streams().size());
+  EXPECT_EQ(kVideoTrack1, vcd->streams()[0].id);
+  EXPECT_EQ(RtpTransceiverDirection::kSendRecv, vcd->direction());
+
+  EXPECT_FALSE(answer->contents()[2].rejected);
+  acd = answer->contents()[2].media_description()->as_audio();
+  ASSERT_EQ(1u, acd->streams().size());
+  EXPECT_EQ(kAudioTrack2, acd->streams()[0].id);
+  EXPECT_EQ(RtpTransceiverDirection::kSendRecv, acd->direction());
+
+  EXPECT_FALSE(answer->contents()[3].rejected);
+  vcd = answer->contents()[3].media_description()->as_video();
+  ASSERT_EQ(1u, vcd->streams().size());
+  EXPECT_EQ(kVideoTrack2, vcd->streams()[0].id);
+  EXPECT_EQ(RtpTransceiverDirection::kSendRecv, vcd->direction());
+}
+
+// Test that the media section will be rejected in offer if the corresponding
+// MediaDescriptionOptions is stopped by the offerer.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       CreateOfferWithMediaSectionStoppedByOfferer) {
+  // Create an offer with two audio sections and one of them is stopped.
+  MediaSessionOptions offer_opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio1",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &offer_opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio2",
+                             RtpTransceiverDirection::kInactive, kStopped,
+                             &offer_opts);
+  std::unique_ptr<SessionDescription> offer =
+      f1_.CreateOffer(offer_opts, nullptr);
+  ASSERT_TRUE(offer);
+  ASSERT_EQ(2u, offer->contents().size());
+  EXPECT_FALSE(offer->contents()[0].rejected);
+  EXPECT_TRUE(offer->contents()[1].rejected);
+}
+
+// Test that the media section will be rejected in answer if the corresponding
+// MediaDescriptionOptions is stopped by the offerer.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       CreateAnswerWithMediaSectionStoppedByOfferer) {
+  // Create an offer with two audio sections and one of them is stopped.
+  MediaSessionOptions offer_opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio1",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &offer_opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio2",
+                             RtpTransceiverDirection::kInactive, kStopped,
+                             &offer_opts);
+  std::unique_ptr<SessionDescription> offer =
+      f1_.CreateOffer(offer_opts, nullptr);
+  ASSERT_TRUE(offer);
+  ASSERT_EQ(2u, offer->contents().size());
+  EXPECT_FALSE(offer->contents()[0].rejected);
+  EXPECT_TRUE(offer->contents()[1].rejected);
+
+  // Create an answer based on the offer.
+  MediaSessionOptions answer_opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio1",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &answer_opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio2",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &answer_opts);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), answer_opts, nullptr);
+  ASSERT_EQ(2u, answer->contents().size());
+  EXPECT_FALSE(answer->contents()[0].rejected);
+  EXPECT_TRUE(answer->contents()[1].rejected);
+}
+
+// Test that the media section will be rejected in answer if the corresponding
+// MediaDescriptionOptions is stopped by the answerer.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       CreateAnswerWithMediaSectionRejectedByAnswerer) {
+  // Create an offer with two audio sections.
+  MediaSessionOptions offer_opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio1",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &offer_opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio2",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &offer_opts);
+  std::unique_ptr<SessionDescription> offer =
+      f1_.CreateOffer(offer_opts, nullptr);
+  ASSERT_TRUE(offer);
+  ASSERT_EQ(2u, offer->contents().size());
+  ASSERT_FALSE(offer->contents()[0].rejected);
+  ASSERT_FALSE(offer->contents()[1].rejected);
+
+  // The answerer rejects one of the audio sections.
+  MediaSessionOptions answer_opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio1",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &answer_opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio2",
+                             RtpTransceiverDirection::kInactive, kStopped,
+                             &answer_opts);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), answer_opts, nullptr);
+  ASSERT_EQ(2u, answer->contents().size());
+  EXPECT_FALSE(answer->contents()[0].rejected);
+  EXPECT_TRUE(answer->contents()[1].rejected);
+
+  // The TransportInfo of the rejected m= section is expected to be added in the
+  // answer.
+  EXPECT_EQ(offer->transport_infos().size(), answer->transport_infos().size());
+}
+
+// Test the generated media sections has the same order of the
+// corresponding MediaDescriptionOptions.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       CreateOfferRespectsMediaDescriptionOptionsOrder) {
+  MediaSessionOptions opts;
+  // This tests put video section first because normally audio comes first by
+  // default.
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+
+  ASSERT_TRUE(offer);
+  ASSERT_EQ(2u, offer->contents().size());
+  EXPECT_EQ("video", offer->contents()[0].name);
+  EXPECT_EQ("audio", offer->contents()[1].name);
+}
+
+// Test that different media sections using the same codec have same payload
+// type.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       PayloadTypesSharedByMediaSectionsOfSameType) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video1",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video2",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  // Create an offer with two video sections using same codecs.
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  ASSERT_TRUE(offer);
+  ASSERT_EQ(2u, offer->contents().size());
+  const VideoContentDescription* vcd1 =
+      offer->contents()[0].media_description()->as_video();
+  const VideoContentDescription* vcd2 =
+      offer->contents()[1].media_description()->as_video();
+  EXPECT_EQ(vcd1->codecs().size(), vcd2->codecs().size());
+  ASSERT_EQ(2u, vcd1->codecs().size());
+  EXPECT_EQ(vcd1->codecs()[0].name, vcd2->codecs()[0].name);
+  EXPECT_EQ(vcd1->codecs()[0].id, vcd2->codecs()[0].id);
+  EXPECT_EQ(vcd1->codecs()[1].name, vcd2->codecs()[1].name);
+  EXPECT_EQ(vcd1->codecs()[1].id, vcd2->codecs()[1].id);
+
+  // Create answer and negotiate the codecs.
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+  ASSERT_TRUE(answer);
+  ASSERT_EQ(2u, answer->contents().size());
+  vcd1 = answer->contents()[0].media_description()->as_video();
+  vcd2 = answer->contents()[1].media_description()->as_video();
+  EXPECT_EQ(vcd1->codecs().size(), vcd2->codecs().size());
+  ASSERT_EQ(1u, vcd1->codecs().size());
+  EXPECT_EQ(vcd1->codecs()[0].name, vcd2->codecs()[0].name);
+  EXPECT_EQ(vcd1->codecs()[0].id, vcd2->codecs()[0].id);
+}
+
+// Test that the codec preference order per media section is respected in
+// subsequent offer.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       CreateOfferRespectsCodecPreferenceOrder) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video1",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video2",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  // Create an offer with two video sections using same codecs.
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  ASSERT_TRUE(offer);
+  ASSERT_EQ(2u, offer->contents().size());
+  VideoContentDescription* vcd1 =
+      offer->contents()[0].media_description()->as_video();
+  const VideoContentDescription* vcd2 =
+      offer->contents()[1].media_description()->as_video();
+  auto video_codecs = MAKE_VECTOR(kVideoCodecs1);
+  EXPECT_EQ(video_codecs, vcd1->codecs());
+  EXPECT_EQ(video_codecs, vcd2->codecs());
+
+  // Change the codec preference of the first video section and create a
+  // follow-up offer.
+  auto video_codecs_reverse = MAKE_VECTOR(kVideoCodecs1Reverse);
+  vcd1->set_codecs(video_codecs_reverse);
+  std::unique_ptr<SessionDescription> updated_offer(
+      f1_.CreateOffer(opts, offer.get()));
+  vcd1 = updated_offer->contents()[0].media_description()->as_video();
+  vcd2 = updated_offer->contents()[1].media_description()->as_video();
+  // The video codec preference order should be respected.
+  EXPECT_EQ(video_codecs_reverse, vcd1->codecs());
+  EXPECT_EQ(video_codecs, vcd2->codecs());
+}
+
+// Test that the codec preference order per media section is respected in
+// the answer.
+TEST_F(MediaSessionDescriptionFactoryTest,
+       CreateAnswerRespectsCodecPreferenceOrder) {
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video1",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video2",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  // Create an offer with two video sections using same codecs.
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  ASSERT_TRUE(offer);
+  ASSERT_EQ(2u, offer->contents().size());
+  VideoContentDescription* vcd1 =
+      offer->contents()[0].media_description()->as_video();
+  const VideoContentDescription* vcd2 =
+      offer->contents()[1].media_description()->as_video();
+  auto video_codecs = MAKE_VECTOR(kVideoCodecs1);
+  EXPECT_EQ(video_codecs, vcd1->codecs());
+  EXPECT_EQ(video_codecs, vcd2->codecs());
+
+  // Change the codec preference of the first video section and create an
+  // answer.
+  auto video_codecs_reverse = MAKE_VECTOR(kVideoCodecs1Reverse);
+  vcd1->set_codecs(video_codecs_reverse);
+  std::unique_ptr<SessionDescription> answer =
+      f1_.CreateAnswer(offer.get(), opts, nullptr);
+  vcd1 = answer->contents()[0].media_description()->as_video();
+  vcd2 = answer->contents()[1].media_description()->as_video();
+  // The video codec preference order should be respected.
+  EXPECT_EQ(video_codecs_reverse, vcd1->codecs());
+  EXPECT_EQ(video_codecs, vcd2->codecs());
+}
+
+// Test that when creating an answer, the codecs use local parameters instead of
+// the remote ones.
+TEST_F(MediaSessionDescriptionFactoryTest, CreateAnswerWithLocalCodecParams) {
+  const std::string audio_param_name = "audio_param";
+  const std::string audio_value1 = "audio_v1";
+  const std::string audio_value2 = "audio_v2";
+  const std::string video_param_name = "video_param";
+  const std::string video_value1 = "video_v1";
+  const std::string video_value2 = "video_v2";
+
+  auto audio_codecs1 = MAKE_VECTOR(kAudioCodecs1);
+  auto audio_codecs2 = MAKE_VECTOR(kAudioCodecs1);
+  auto video_codecs1 = MAKE_VECTOR(kVideoCodecs1);
+  auto video_codecs2 = MAKE_VECTOR(kVideoCodecs1);
+
+  // Set the parameters for codecs.
+  audio_codecs1[0].SetParam(audio_param_name, audio_value1);
+  video_codecs1[0].SetParam(video_param_name, video_value1);
+  audio_codecs2[0].SetParam(audio_param_name, audio_value2);
+  video_codecs2[0].SetParam(video_param_name, video_value2);
+
+  f1_.set_audio_codecs(audio_codecs1, audio_codecs1);
+  f1_.set_video_codecs(video_codecs1, video_codecs1);
+  f2_.set_audio_codecs(audio_codecs2, audio_codecs2);
+  f2_.set_video_codecs(video_codecs2, video_codecs2);
+
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  ASSERT_TRUE(offer);
+  auto offer_acd = offer->contents()[0].media_description()->as_audio();
+  auto offer_vcd = offer->contents()[1].media_description()->as_video();
+  std::string value;
+  EXPECT_TRUE(offer_acd->codecs()[0].GetParam(audio_param_name, &value));
+  EXPECT_EQ(audio_value1, value);
+  EXPECT_TRUE(offer_vcd->codecs()[0].GetParam(video_param_name, &value));
+  EXPECT_EQ(video_value1, value);
+
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+  ASSERT_TRUE(answer);
+  auto answer_acd = answer->contents()[0].media_description()->as_audio();
+  auto answer_vcd = answer->contents()[1].media_description()->as_video();
+  // Use the parameters from the local codecs.
+  EXPECT_TRUE(answer_acd->codecs()[0].GetParam(audio_param_name, &value));
+  EXPECT_EQ(audio_value2, value);
+  EXPECT_TRUE(answer_vcd->codecs()[0].GetParam(video_param_name, &value));
+  EXPECT_EQ(video_value2, value);
+}
+
+// Test that matching packetization-mode is part of the criteria for matching
+// H264 codecs (in addition to profile-level-id). Previously, this was not the
+// case, so the first H264 codec with the same profile-level-id would match and
+// the payload type in the answer would be incorrect.
+// This is a regression test for bugs.webrtc.org/8808
+TEST_F(MediaSessionDescriptionFactoryTest,
+       H264MatchCriteriaIncludesPacketizationMode) {
+  // Create two H264 codecs with the same profile level ID and different
+  // packetization modes.
+  VideoCodec h264_pm0(96, "H264");
+  h264_pm0.params[cricket::kH264FmtpProfileLevelId] = "42c01f";
+  h264_pm0.params[cricket::kH264FmtpPacketizationMode] = "0";
+  VideoCodec h264_pm1(97, "H264");
+  h264_pm1.params[cricket::kH264FmtpProfileLevelId] = "42c01f";
+  h264_pm1.params[cricket::kH264FmtpPacketizationMode] = "1";
+
+  // Offerer will send both codecs, answerer should choose the one with matching
+  // packetization mode (and not the first one it sees).
+  f1_.set_video_codecs({h264_pm0, h264_pm1}, {h264_pm0, h264_pm1});
+  f2_.set_video_codecs({h264_pm1}, {h264_pm1});
+
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
+                             RtpTransceiverDirection::kSendRecv, kActive,
+                             &opts);
+
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  ASSERT_TRUE(offer);
+
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+  ASSERT_TRUE(answer);
+
+  // Answer should have one negotiated codec with packetization-mode=1 using the
+  // offered payload type.
+  ASSERT_EQ(1u, answer->contents().size());
+  auto answer_vcd = answer->contents()[0].media_description()->as_video();
+  ASSERT_EQ(1u, answer_vcd->codecs().size());
+  auto answer_codec = answer_vcd->codecs()[0];
+  EXPECT_EQ(h264_pm1.id, answer_codec.id);
+}
+
+class MediaProtocolTest : public ::testing::TestWithParam<const char*> {
+ public:
+  MediaProtocolTest()
+      : tdf1_(field_trials_),
+        tdf2_(field_trials_),
+        f1_(&tdf1_, &ssrc_generator1),
+        f2_(&tdf2_, &ssrc_generator2) {
+    f1_.set_audio_codecs(MAKE_VECTOR(kAudioCodecs1),
+                         MAKE_VECTOR(kAudioCodecs1));
+    f1_.set_video_codecs(MAKE_VECTOR(kVideoCodecs1),
+                         MAKE_VECTOR(kVideoCodecs1));
+    f2_.set_audio_codecs(MAKE_VECTOR(kAudioCodecs2),
+                         MAKE_VECTOR(kAudioCodecs2));
+    f2_.set_video_codecs(MAKE_VECTOR(kVideoCodecs2),
+                         MAKE_VECTOR(kVideoCodecs2));
+    f1_.set_secure(SEC_ENABLED);
+    f2_.set_secure(SEC_ENABLED);
+    tdf1_.set_certificate(rtc::RTCCertificate::Create(
+        std::unique_ptr<rtc::SSLIdentity>(new rtc::FakeSSLIdentity("id1"))));
+    tdf2_.set_certificate(rtc::RTCCertificate::Create(
+        std::unique_ptr<rtc::SSLIdentity>(new rtc::FakeSSLIdentity("id2"))));
+    tdf1_.set_secure(SEC_ENABLED);
+    tdf2_.set_secure(SEC_ENABLED);
+  }
+
+ protected:
+  webrtc::test::ScopedKeyValueConfig field_trials_;
+  TransportDescriptionFactory tdf1_;
+  TransportDescriptionFactory tdf2_;
+  MediaSessionDescriptionFactory f1_;
+  MediaSessionDescriptionFactory f2_;
+  UniqueRandomIdGenerator ssrc_generator1;
+  UniqueRandomIdGenerator ssrc_generator2;
+};
+
+TEST_P(MediaProtocolTest, TestAudioVideoAcceptance) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  ASSERT_TRUE(offer.get() != nullptr);
+  // Set the protocol for all the contents.
+  for (auto& content : offer.get()->contents()) {
+    content.media_description()->set_protocol(GetParam());
+  }
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+  const ContentInfo* ac = answer->GetContentByName("audio");
+  const ContentInfo* vc = answer->GetContentByName("video");
+  ASSERT_TRUE(ac != nullptr);
+  ASSERT_TRUE(vc != nullptr);
+  EXPECT_FALSE(ac->rejected);  // the offer is accepted
+  EXPECT_FALSE(vc->rejected);
+  const AudioContentDescription* acd = ac->media_description()->as_audio();
+  const VideoContentDescription* vcd = vc->media_description()->as_video();
+  EXPECT_EQ(GetParam(), acd->protocol());
+  EXPECT_EQ(GetParam(), vcd->protocol());
+}
+
+INSTANTIATE_TEST_SUITE_P(MediaProtocolPatternTest,
+                         MediaProtocolTest,
+                         ::testing::ValuesIn(kMediaProtocols));
+INSTANTIATE_TEST_SUITE_P(MediaProtocolDtlsPatternTest,
+                         MediaProtocolTest,
+                         ::testing::ValuesIn(kMediaProtocolsDtls));
+
+TEST_F(MediaSessionDescriptionFactoryTest, TestSetAudioCodecs) {
+  webrtc::test::ScopedKeyValueConfig field_trials;
+  TransportDescriptionFactory tdf(field_trials);
+  UniqueRandomIdGenerator ssrc_generator;
+  MediaSessionDescriptionFactory sf(&tdf, &ssrc_generator);
+  std::vector<AudioCodec> send_codecs = MAKE_VECTOR(kAudioCodecs1);
+  std::vector<AudioCodec> recv_codecs = MAKE_VECTOR(kAudioCodecs2);
+
+  // The merged list of codecs should contain any send codecs that are also
+  // nominally in the receive codecs list. Payload types should be picked from
+  // the send codecs and a number-of-channels of 0 and 1 should be equivalent
+  // (set to 1). This equals what happens when the send codecs are used in an
+  // offer and the receive codecs are used in the following answer.
+  const std::vector<AudioCodec> sendrecv_codecs =
+      MAKE_VECTOR(kAudioCodecsAnswer);
+  const std::vector<AudioCodec> no_codecs;
+
+  RTC_CHECK_EQ(send_codecs[1].name, "iLBC")
+      << "Please don't change shared test data!";
+  RTC_CHECK_EQ(recv_codecs[2].name, "iLBC")
+      << "Please don't change shared test data!";
+  // Alter iLBC send codec to have zero channels, to test that that is handled
+  // properly.
+  send_codecs[1].channels = 0;
+
+  // Alter iLBC receive codec to be lowercase, to test that case conversions
+  // are handled properly.
+  recv_codecs[2].name = "ilbc";
+
+  // Test proper merge
+  sf.set_audio_codecs(send_codecs, recv_codecs);
+  EXPECT_EQ(send_codecs, sf.audio_send_codecs());
+  EXPECT_EQ(recv_codecs, sf.audio_recv_codecs());
+  EXPECT_EQ(sendrecv_codecs, sf.audio_sendrecv_codecs());
+
+  // Test empty send codecs list
+  sf.set_audio_codecs(no_codecs, recv_codecs);
+  EXPECT_EQ(no_codecs, sf.audio_send_codecs());
+  EXPECT_EQ(recv_codecs, sf.audio_recv_codecs());
+  EXPECT_EQ(no_codecs, sf.audio_sendrecv_codecs());
+
+  // Test empty recv codecs list
+  sf.set_audio_codecs(send_codecs, no_codecs);
+  EXPECT_EQ(send_codecs, sf.audio_send_codecs());
+  EXPECT_EQ(no_codecs, sf.audio_recv_codecs());
+  EXPECT_EQ(no_codecs, sf.audio_sendrecv_codecs());
+
+  // Test all empty codec lists
+  sf.set_audio_codecs(no_codecs, no_codecs);
+  EXPECT_EQ(no_codecs, sf.audio_send_codecs());
+  EXPECT_EQ(no_codecs, sf.audio_recv_codecs());
+  EXPECT_EQ(no_codecs, sf.audio_sendrecv_codecs());
+}
+
+namespace {
+// Compare the two vectors of codecs ignoring the payload type.
+template <class Codec>
+bool CodecsMatch(const std::vector<Codec>& codecs1,
+                 const std::vector<Codec>& codecs2,
+                 const webrtc::FieldTrialsView* field_trials) {
+  if (codecs1.size() != codecs2.size()) {
+    return false;
+  }
+
+  for (size_t i = 0; i < codecs1.size(); ++i) {
+    if (!codecs1[i].Matches(codecs2[i], field_trials)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+void TestAudioCodecsOffer(RtpTransceiverDirection direction) {
+  webrtc::test::ScopedKeyValueConfig field_trials;
+  TransportDescriptionFactory tdf(field_trials);
+  UniqueRandomIdGenerator ssrc_generator;
+  MediaSessionDescriptionFactory sf(&tdf, &ssrc_generator);
+  const std::vector<AudioCodec> send_codecs = MAKE_VECTOR(kAudioCodecs1);
+  const std::vector<AudioCodec> recv_codecs = MAKE_VECTOR(kAudioCodecs2);
+  const std::vector<AudioCodec> sendrecv_codecs =
+      MAKE_VECTOR(kAudioCodecsAnswer);
+  sf.set_audio_codecs(send_codecs, recv_codecs);
+
+  MediaSessionOptions opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio", direction, kActive,
+                             &opts);
+
+  if (direction == RtpTransceiverDirection::kSendRecv ||
+      direction == RtpTransceiverDirection::kSendOnly) {
+    AttachSenderToMediaDescriptionOptions(
+        "audio", MEDIA_TYPE_AUDIO, kAudioTrack1, {kMediaStream1}, 1, &opts);
+  }
+
+  std::unique_ptr<SessionDescription> offer = sf.CreateOffer(opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+  ContentInfo* ac = offer->GetContentByName("audio");
+
+  // If the factory didn't add any audio content to the offer, we cannot check
+  // that the codecs put in are right. This happens when we neither want to
+  // send nor receive audio. The checks are still in place if at some point
+  // we'd instead create an inactive stream.
+  if (ac) {
+    AudioContentDescription* acd = ac->media_description()->as_audio();
+    // sendrecv and inactive should both present lists as if the channel was
+    // to be used for sending and receiving. Inactive essentially means it
+    // might eventually be used anything, but we don't know more at this
+    // moment.
+    if (acd->direction() == RtpTransceiverDirection::kSendOnly) {
+      EXPECT_TRUE(
+          CodecsMatch<AudioCodec>(send_codecs, acd->codecs(), &field_trials));
+    } else if (acd->direction() == RtpTransceiverDirection::kRecvOnly) {
+      EXPECT_TRUE(
+          CodecsMatch<AudioCodec>(recv_codecs, acd->codecs(), &field_trials));
+    } else {
+      EXPECT_TRUE(CodecsMatch<AudioCodec>(sendrecv_codecs, acd->codecs(),
+                                          &field_trials));
+    }
+  }
+}
+
+static const AudioCodec kOfferAnswerCodecs[] = {
+    AudioCodec(0, "codec0", 16000, -1, 1),
+    AudioCodec(1, "codec1", 8000, 13300, 1),
+    AudioCodec(2, "codec2", 8000, 64000, 1),
+    AudioCodec(3, "codec3", 8000, 64000, 1),
+    AudioCodec(4, "codec4", 8000, 0, 2),
+    AudioCodec(5, "codec5", 32000, 0, 1),
+    AudioCodec(6, "codec6", 48000, 0, 1)};
+
+/* The codecs groups below are chosen as per the matrix below. The objective
+ * is to have different sets of codecs in the inputs, to get unique sets of
+ * codecs after negotiation, depending on offer and answer communication
+ * directions. One-way directions in the offer should either result in the
+ * opposite direction in the answer, or an inactive answer. Regardless, the
+ * choice of codecs should be as if the answer contained the opposite
+ * direction. Inactive offers should be treated as sendrecv/sendrecv.
+ *
+ *         |     Offer   |      Answer  |         Result
+ *    codec|send recv sr | send recv sr | s/r  r/s sr/s sr/r sr/sr
+ *     0   | x    -    - |  -    x    - |  x    -    -    -    -
+ *     1   | x    x    x |  -    x    - |  x    -    -    x    -
+ *     2   | -    x    - |  x    -    - |  -    x    -    -    -
+ *     3   | x    x    x |  x    -    - |  -    x    x    -    -
+ *     4   | -    x    - |  x    x    x |  -    x    -    -    -
+ *     5   | x    -    - |  x    x    x |  x    -    -    -    -
+ *     6   | x    x    x |  x    x    x |  x    x    x    x    x
+ */
+// Codecs used by offerer in the AudioCodecsAnswerTest
+static const int kOfferSendCodecs[] = {0, 1, 3, 5, 6};
+static const int kOfferRecvCodecs[] = {1, 2, 3, 4, 6};
+// Codecs used in the answerer in the AudioCodecsAnswerTest.  The order is
+// jumbled to catch the answer not following the order in the offer.
+static const int kAnswerSendCodecs[] = {6, 5, 2, 3, 4};
+static const int kAnswerRecvCodecs[] = {6, 5, 4, 1, 0};
+// The resulting sets of codecs in the answer in the AudioCodecsAnswerTest
+static const int kResultSend_RecvCodecs[] = {0, 1, 5, 6};
+static const int kResultRecv_SendCodecs[] = {2, 3, 4, 6};
+static const int kResultSendrecv_SendCodecs[] = {3, 6};
+static const int kResultSendrecv_RecvCodecs[] = {1, 6};
+static const int kResultSendrecv_SendrecvCodecs[] = {6};
+
+template <typename T, int IDXS>
+std::vector<T> VectorFromIndices(const T* array, const int (&indices)[IDXS]) {
+  std::vector<T> out;
+  out.reserve(IDXS);
+  for (int idx : indices)
+    out.push_back(array[idx]);
+
+  return out;
+}
+
+void TestAudioCodecsAnswer(RtpTransceiverDirection offer_direction,
+                           RtpTransceiverDirection answer_direction,
+                           bool add_legacy_stream) {
+  webrtc::test::ScopedKeyValueConfig field_trials;
+  TransportDescriptionFactory offer_tdf(field_trials);
+  TransportDescriptionFactory answer_tdf(field_trials);
+  UniqueRandomIdGenerator ssrc_generator1, ssrc_generator2;
+  MediaSessionDescriptionFactory offer_factory(&offer_tdf, &ssrc_generator1);
+  MediaSessionDescriptionFactory answer_factory(&answer_tdf, &ssrc_generator2);
+
+  offer_factory.set_audio_codecs(
+      VectorFromIndices(kOfferAnswerCodecs, kOfferSendCodecs),
+      VectorFromIndices(kOfferAnswerCodecs, kOfferRecvCodecs));
+  answer_factory.set_audio_codecs(
+      VectorFromIndices(kOfferAnswerCodecs, kAnswerSendCodecs),
+      VectorFromIndices(kOfferAnswerCodecs, kAnswerRecvCodecs));
+
+  MediaSessionOptions offer_opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio", offer_direction,
+                             kActive, &offer_opts);
+
+  if (webrtc::RtpTransceiverDirectionHasSend(offer_direction)) {
+    AttachSenderToMediaDescriptionOptions("audio", MEDIA_TYPE_AUDIO,
+                                          kAudioTrack1, {kMediaStream1}, 1,
+                                          &offer_opts);
+  }
+
+  std::unique_ptr<SessionDescription> offer =
+      offer_factory.CreateOffer(offer_opts, NULL);
+  ASSERT_TRUE(offer.get() != NULL);
+
+  MediaSessionOptions answer_opts;
+  AddMediaDescriptionOptions(MEDIA_TYPE_AUDIO, "audio", answer_direction,
+                             kActive, &answer_opts);
+
+  if (webrtc::RtpTransceiverDirectionHasSend(answer_direction)) {
+    AttachSenderToMediaDescriptionOptions("audio", MEDIA_TYPE_AUDIO,
+                                          kAudioTrack1, {kMediaStream1}, 1,
+                                          &answer_opts);
+  }
+  std::unique_ptr<SessionDescription> answer =
+      answer_factory.CreateAnswer(offer.get(), answer_opts, NULL);
+  const ContentInfo* ac = answer->GetContentByName("audio");
+
+  // If the factory didn't add any audio content to the answer, we cannot
+  // check that the codecs put in are right. This happens when we neither want
+  // to send nor receive audio. The checks are still in place if at some point
+  // we'd instead create an inactive stream.
+  if (ac) {
+    ASSERT_EQ(MEDIA_TYPE_AUDIO, ac->media_description()->type());
+    const AudioContentDescription* acd = ac->media_description()->as_audio();
+
+    std::vector<AudioCodec> target_codecs;
+    // For offers with sendrecv or inactive, we should never reply with more
+    // codecs than offered, with these codec sets.
+    switch (offer_direction) {
+      case RtpTransceiverDirection::kInactive:
+        target_codecs = VectorFromIndices(kOfferAnswerCodecs,
+                                          kResultSendrecv_SendrecvCodecs);
+        break;
+      case RtpTransceiverDirection::kSendOnly:
+        target_codecs =
+            VectorFromIndices(kOfferAnswerCodecs, kResultSend_RecvCodecs);
+        break;
+      case RtpTransceiverDirection::kRecvOnly:
+        target_codecs =
+            VectorFromIndices(kOfferAnswerCodecs, kResultRecv_SendCodecs);
+        break;
+      case RtpTransceiverDirection::kSendRecv:
+        if (acd->direction() == RtpTransceiverDirection::kSendOnly) {
+          target_codecs =
+              VectorFromIndices(kOfferAnswerCodecs, kResultSendrecv_SendCodecs);
+        } else if (acd->direction() == RtpTransceiverDirection::kRecvOnly) {
+          target_codecs =
+              VectorFromIndices(kOfferAnswerCodecs, kResultSendrecv_RecvCodecs);
+        } else {
+          target_codecs = VectorFromIndices(kOfferAnswerCodecs,
+                                            kResultSendrecv_SendrecvCodecs);
+        }
+        break;
+      case RtpTransceiverDirection::kStopped:
+        // This does not happen in any current test.
+        RTC_DCHECK_NOTREACHED();
+    }
+
+    auto format_codecs = [](const std::vector<AudioCodec>& codecs) {
+      rtc::StringBuilder os;
+      bool first = true;
+      os << "{";
+      for (const auto& c : codecs) {
+        os << (first ? " " : ", ") << c.id;
+        first = false;
+      }
+      os << " }";
+      return os.Release();
+    };
+
+    EXPECT_TRUE(acd->codecs() == target_codecs)
+        << "Expected: " << format_codecs(target_codecs)
+        << ", got: " << format_codecs(acd->codecs()) << "; Offered: "
+        << webrtc::RtpTransceiverDirectionToString(offer_direction)
+        << ", answerer wants: "
+        << webrtc::RtpTransceiverDirectionToString(answer_direction)
+        << "; got: "
+        << webrtc::RtpTransceiverDirectionToString(acd->direction());
+  } else {
+    EXPECT_EQ(offer_direction, RtpTransceiverDirection::kInactive)
+        << "Only inactive offers are allowed to not generate any audio "
+           "content";
+  }
+}
+
+}  // namespace
+
+class AudioCodecsOfferTest
+    : public ::testing::TestWithParam<RtpTransceiverDirection> {};
+
+TEST_P(AudioCodecsOfferTest, TestCodecsInOffer) {
+  TestAudioCodecsOffer(GetParam());
+}
+
+INSTANTIATE_TEST_SUITE_P(MediaSessionDescriptionFactoryTest,
+                         AudioCodecsOfferTest,
+                         ::testing::Values(RtpTransceiverDirection::kSendOnly,
+                                           RtpTransceiverDirection::kRecvOnly,
+                                           RtpTransceiverDirection::kSendRecv,
+                                           RtpTransceiverDirection::kInactive));
+
+class AudioCodecsAnswerTest
+    : public ::testing::TestWithParam<::testing::tuple<RtpTransceiverDirection,
+                                                       RtpTransceiverDirection,
+                                                       bool>> {};
+
+TEST_P(AudioCodecsAnswerTest, TestCodecsInAnswer) {
+  TestAudioCodecsAnswer(::testing::get<0>(GetParam()),
+                        ::testing::get<1>(GetParam()),
+                        ::testing::get<2>(GetParam()));
+}
+
+INSTANTIATE_TEST_SUITE_P(
+    MediaSessionDescriptionFactoryTest,
+    AudioCodecsAnswerTest,
+    ::testing::Combine(::testing::Values(RtpTransceiverDirection::kSendOnly,
+                                         RtpTransceiverDirection::kRecvOnly,
+                                         RtpTransceiverDirection::kSendRecv,
+                                         RtpTransceiverDirection::kInactive),
+                       ::testing::Values(RtpTransceiverDirection::kSendOnly,
+                                         RtpTransceiverDirection::kRecvOnly,
+                                         RtpTransceiverDirection::kSendRecv,
+                                         RtpTransceiverDirection::kInactive),
+                       ::testing::Bool()));