1 files changed, 109 insertions, 0 deletions
diff --git a/third_party/libwebrtc/modules/rtp_rtcp/source/remote_ntp_time_estimator.cc b/third_party/libwebrtc/modules/rtp_rtcp/source/remote_ntp_time_estimator.cc
new file mode 100644
index 0000000000..6f90cd175c
--- /dev/null
+++ b/third_party/libwebrtc/modules/rtp_rtcp/source/remote_ntp_time_estimator.cc
@@ -0,0 +1,109 @@
+/*
+ *  Copyright (c) 2014 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 "modules/rtp_rtcp/include/remote_ntp_time_estimator.h"
+
+#include <cstdint>
+
+#include "modules/rtp_rtcp/source/time_util.h"
+#include "rtc_base/logging.h"
+#include "system_wrappers/include/clock.h"
+#include "system_wrappers/include/ntp_time.h"
+
+namespace webrtc {
+
+namespace {
+
+constexpr int kMinimumNumberOfSamples = 2;
+constexpr TimeDelta kTimingLogInterval = TimeDelta::Seconds(10);
+constexpr int kClocksOffsetSmoothingWindow = 100;
+
+// Subtracts two NtpTime values keeping maximum precision.
+int64_t Subtract(NtpTime minuend, NtpTime subtrahend) {
+  uint64_t a = static_cast<uint64_t>(minuend);
+  uint64_t b = static_cast<uint64_t>(subtrahend);
+  return a >= b ? static_cast<int64_t>(a - b) : -static_cast<int64_t>(b - a);
+}
+
+NtpTime Add(NtpTime lhs, int64_t rhs) {
+  uint64_t result = static_cast<uint64_t>(lhs);
+  if (rhs >= 0) {
+    result += static_cast<uint64_t>(rhs);
+  } else {
+    result -= static_cast<uint64_t>(-rhs);
+  }
+  return NtpTime(result);
+}
+
+}  // namespace
+
+// TODO(wu): Refactor this class so that it can be shared with
+// vie_sync_module.cc.
+RemoteNtpTimeEstimator::RemoteNtpTimeEstimator(Clock* clock)
+    : clock_(clock),
+      ntp_clocks_offset_estimator_(kClocksOffsetSmoothingWindow) {}
+
+bool RemoteNtpTimeEstimator::UpdateRtcpTimestamp(TimeDelta rtt,
+                                                 NtpTime sender_send_time,
+                                                 uint32_t rtp_timestamp) {
+  switch (rtp_to_ntp_.UpdateMeasurements(sender_send_time, rtp_timestamp)) {
+    case RtpToNtpEstimator::kInvalidMeasurement:
+      return false;
+    case RtpToNtpEstimator::kSameMeasurement:
+      // No new RTCP SR since last time this function was called.
+      return true;
+    case RtpToNtpEstimator::kNewMeasurement:
+      break;
+  }
+
+  // Assume connection is symmetric and thus time to deliver the packet is half
+  // the round trip time.
+  int64_t deliver_time_ntp = ToNtpUnits(rtt) / 2;
+
+  // Update extrapolator with the new arrival time.
+  NtpTime receiver_arrival_time = clock_->CurrentNtpTime();
+  int64_t remote_to_local_clocks_offset =
+      Subtract(receiver_arrival_time, sender_send_time) - deliver_time_ntp;
+  ntp_clocks_offset_estimator_.Insert(remote_to_local_clocks_offset);
+  return true;
+}
+
+NtpTime RemoteNtpTimeEstimator::EstimateNtp(uint32_t rtp_timestamp) {
+  NtpTime sender_capture = rtp_to_ntp_.Estimate(rtp_timestamp);
+  if (!sender_capture.Valid()) {
+    return sender_capture;
+  }
+
+  int64_t remote_to_local_clocks_offset =
+      ntp_clocks_offset_estimator_.GetFilteredValue();
+  NtpTime receiver_capture = Add(sender_capture, remote_to_local_clocks_offset);
+
+  Timestamp now = clock_->CurrentTime();
+  if (now - last_timing_log_ > kTimingLogInterval) {
+    RTC_LOG(LS_INFO) << "RTP timestamp: " << rtp_timestamp
+                     << " in NTP clock: " << sender_capture.ToMs()
+                     << " estimated time in receiver NTP clock: "
+                     << receiver_capture.ToMs();
+    last_timing_log_ = now;
+  }
+
+  return receiver_capture;
+}
+
+absl::optional<int64_t>
+RemoteNtpTimeEstimator::EstimateRemoteToLocalClockOffset() {
+  if (ntp_clocks_offset_estimator_.GetNumberOfSamplesStored() <
+      kMinimumNumberOfSamples) {
+    return absl::nullopt;
+  }
+  return ntp_clocks_offset_estimator_.GetFilteredValue();
+}
+
+}  // namespace webrtc