1 files changed, 181 insertions, 0 deletions
diff --git a/dom/media/webm/EbmlComposer.cpp b/dom/media/webm/EbmlComposer.cpp
new file mode 100644
index 0000000000..7a83b8664c
--- /dev/null
+++ b/dom/media/webm/EbmlComposer.cpp
@@ -0,0 +1,181 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-*/
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "EbmlComposer.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/EndianUtils.h"
+#include "libmkv/EbmlIDs.h"
+#include "libmkv/EbmlWriter.h"
+#include "libmkv/WebMElement.h"
+#include "prtime.h"
+#include "limits.h"
+
+namespace mozilla {
+
+// Timecode scale in nanoseconds
+constexpr unsigned long TIME_CODE_SCALE = 1000000;
+// The WebM header size without audio CodecPrivateData
+constexpr int32_t DEFAULT_HEADER_SIZE = 1024;
+// Number of milliseconds after which we flush audio-only clusters
+constexpr int32_t FLUSH_AUDIO_ONLY_AFTER_MS = 1000;
+
+void EbmlComposer::GenerateHeader() {
+  MOZ_RELEASE_ASSERT(!mMetadataFinished);
+  MOZ_RELEASE_ASSERT(mHasAudio || mHasVideo);
+
+  // Write the EBML header.
+  EbmlGlobal ebml;
+  // The WEbM header default size usually smaller than 1k.
+  auto buffer =
+      MakeUnique<uint8_t[]>(DEFAULT_HEADER_SIZE + mCodecPrivateData.Length());
+  ebml.buf = buffer.get();
+  ebml.offset = 0;
+  writeHeader(&ebml);
+  {
+    EbmlLoc segEbmlLoc, ebmlLocseg, ebmlLoc;
+    Ebml_StartSubElement(&ebml, &segEbmlLoc, Segment);
+    {
+      Ebml_StartSubElement(&ebml, &ebmlLocseg, SeekHead);
+      // Todo: We don't know the exact sizes of encoded data and
+      // ignore this section.
+      Ebml_EndSubElement(&ebml, &ebmlLocseg);
+      writeSegmentInformation(&ebml, &ebmlLoc, TIME_CODE_SCALE, 0);
+      {
+        EbmlLoc trackLoc;
+        Ebml_StartSubElement(&ebml, &trackLoc, Tracks);
+        {
+          // Video
+          if (mWidth > 0 && mHeight > 0) {
+            writeVideoTrack(&ebml, 0x1, 0, "V_VP8", mWidth, mHeight,
+                            mDisplayWidth, mDisplayHeight);
+          }
+          // Audio
+          if (mCodecPrivateData.Length() > 0) {
+            // Extract the pre-skip from mCodecPrivateData
+            // then convert it to nanoseconds.
+            // For more details see
+            // https://tools.ietf.org/html/rfc7845#section-4.2
+            uint64_t codecDelay = (uint64_t)LittleEndian::readUint16(
+                                      mCodecPrivateData.Elements() + 10) *
+                                  PR_NSEC_PER_SEC / 48000;
+            // Fixed 80ms, convert into nanoseconds.
+            uint64_t seekPreRoll = 80 * PR_NSEC_PER_MSEC;
+            writeAudioTrack(&ebml, 0x2, 0x0, "A_OPUS", mSampleFreq, mChannels,
+                            codecDelay, seekPreRoll,
+                            mCodecPrivateData.Elements(),
+                            mCodecPrivateData.Length());
+          }
+        }
+        Ebml_EndSubElement(&ebml, &trackLoc);
+      }
+    }
+    // The Recording length is unknown and
+    // ignore write the whole Segment element size
+  }
+  MOZ_ASSERT(ebml.offset <= DEFAULT_HEADER_SIZE + mCodecPrivateData.Length(),
+             "write more data > EBML_BUFFER_SIZE");
+  auto block = mBuffer.AppendElement();
+  block->SetLength(ebml.offset);
+  memcpy(block->Elements(), ebml.buf, ebml.offset);
+  mMetadataFinished = true;
+}
+
+nsresult EbmlComposer::WriteSimpleBlock(EncodedFrame* aFrame) {
+  MOZ_RELEASE_ASSERT(mMetadataFinished);
+  auto frameType = aFrame->mFrameType;
+  const bool isVP8IFrame = (frameType == EncodedFrame::FrameType::VP8_I_FRAME);
+  const bool isVP8PFrame = (frameType == EncodedFrame::FrameType::VP8_P_FRAME);
+  const bool isOpus = (frameType == EncodedFrame::FrameType::OPUS_AUDIO_FRAME);
+
+  MOZ_ASSERT_IF(isVP8IFrame, mHasVideo);
+  MOZ_ASSERT_IF(isVP8PFrame, mHasVideo);
+  MOZ_ASSERT_IF(isOpus, mHasAudio);
+
+  if (isVP8PFrame && !mHasWrittenCluster) {
+    // We ensure there is a cluster header and an I-frame prior to any P-frame.
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  int64_t timeCode = aFrame->mTime.ToMicroseconds() / PR_USEC_PER_MSEC -
+                     mCurrentClusterTimecode;
+
+  const bool needClusterHeader =
+      !mHasWrittenCluster ||
+      (!mHasVideo && timeCode >= FLUSH_AUDIO_ONLY_AFTER_MS) || isVP8IFrame;
+
+  auto block = mBuffer.AppendElement();
+  block->SetLength(aFrame->mFrameData->Length() + DEFAULT_HEADER_SIZE);
+
+  EbmlGlobal ebml;
+  ebml.offset = 0;
+  ebml.buf = block->Elements();
+
+  if (needClusterHeader) {
+    mHasWrittenCluster = true;
+    EbmlLoc ebmlLoc;
+    // This starts the Cluster element. Note that we never end this element
+    // through Ebml_EndSubElement. What the ending would allow us to do is write
+    // the full length of the cluster in the element header. That would also
+    // force us to keep the entire cluster in memory until we know where it
+    // ends. Now it instead ends through the start of the next cluster. This
+    // allows us to stream the muxed data with much lower latency than if we
+    // would have to wait for clusters to end.
+    Ebml_StartSubElement(&ebml, &ebmlLoc, Cluster);
+    // if timeCode didn't under/overflow before, it shouldn't after this
+    mCurrentClusterTimecode = aFrame->mTime.ToMicroseconds() / PR_USEC_PER_MSEC;
+    Ebml_SerializeUnsigned(&ebml, Timecode, mCurrentClusterTimecode);
+
+    // Can't under-/overflow now
+    timeCode = 0;
+  }
+
+  MOZ_RELEASE_ASSERT(timeCode >= SHRT_MIN);
+  MOZ_RELEASE_ASSERT(timeCode <= SHRT_MAX);
+
+  writeSimpleBlock(&ebml, isOpus ? 0x2 : 0x1, static_cast<short>(timeCode),
+                   isVP8IFrame, 0, 0,
+                   (unsigned char*)aFrame->mFrameData->Elements(),
+                   aFrame->mFrameData->Length());
+  MOZ_ASSERT(ebml.offset <= DEFAULT_HEADER_SIZE + aFrame->mFrameData->Length(),
+             "write more data > EBML_BUFFER_SIZE");
+  block->SetLength(ebml.offset);
+
+  return NS_OK;
+}
+
+void EbmlComposer::SetVideoConfig(uint32_t aWidth, uint32_t aHeight,
+                                  uint32_t aDisplayWidth,
+                                  uint32_t aDisplayHeight) {
+  MOZ_RELEASE_ASSERT(!mMetadataFinished);
+  MOZ_ASSERT(aWidth > 0, "Width should > 0");
+  MOZ_ASSERT(aHeight > 0, "Height should > 0");
+  MOZ_ASSERT(aDisplayWidth > 0, "DisplayWidth should > 0");
+  MOZ_ASSERT(aDisplayHeight > 0, "DisplayHeight should > 0");
+  mWidth = aWidth;
+  mHeight = aHeight;
+  mDisplayWidth = aDisplayWidth;
+  mDisplayHeight = aDisplayHeight;
+  mHasVideo = true;
+}
+
+void EbmlComposer::SetAudioConfig(uint32_t aSampleFreq, uint32_t aChannels) {
+  MOZ_RELEASE_ASSERT(!mMetadataFinished);
+  MOZ_ASSERT(aSampleFreq > 0, "SampleFreq should > 0");
+  MOZ_ASSERT(aChannels > 0, "Channels should > 0");
+  mSampleFreq = aSampleFreq;
+  mChannels = aChannels;
+  mHasAudio = true;
+}
+
+void EbmlComposer::ExtractBuffer(nsTArray<nsTArray<uint8_t> >* aDestBufs,
+                                 uint32_t aFlag) {
+  if (!mMetadataFinished) {
+    return;
+  }
+  aDestBufs->AppendElements(std::move(mBuffer));
+  MOZ_ASSERT(mBuffer.IsEmpty());
+}
+
+}  // namespace mozilla