MSE: Emit a MEDIA_LOG warning on muxed sequence append mode attempt

Due to spec-compliant processing of muxed sequence mode appends
producing problematic results following discontinuities in the muxed
media, this change adds a warning to chrome://media-internals if such an
append is detected. I've also revived spec discussion on this by filing
w3c/media-source#186

BUG=728477

Change-Id: I78858ff9c0982eb76bcdb907a7a3fcfdb5d36b87
Reviewed-on: https://chromium-review.googlesource.com/546963
Commit-Queue: Matthew Wolenetz <wolenetz@chromium.org>
Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#483240}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 3a083529baf8043e94aa394b810acdc320d953c8

base/test_helpers.h

@@ -165,6 +165,12 @@ MATCHER_P(SegmentMissingFrames, track_id, "") {
                std::string(track_id));
 }
 
+MATCHER(MuxedSequenceModeWarning, "") {
+  return CONTAINS_STRING(arg,
+                         "Warning: using MSE 'sequence' AppendMode for a "
+                         "SourceBuffer with multiple tracks");
+}
+
 MATCHER(StreamParsingFailed, "") {
   return CONTAINS_STRING(arg, "Append: stream parsing failed.");
 }

filters/chunk_demuxer_unittest.cc

@@ -4770,6 +4770,34 @@ TEST_F(ChunkDemuxerTest, RemovingIdMustRemoveStreams) {
   EXPECT_EQ(nullptr, GetStream(DemuxerStream::VIDEO));
 }
 
+TEST_F(ChunkDemuxerTest, SequenceModeMuxedAppendShouldWarn) {
+  ASSERT_TRUE(InitDemuxer(HAS_AUDIO | HAS_VIDEO));
+
+  demuxer_->SetSequenceMode(kSourceId, true);
+  EXPECT_MEDIA_LOG(MuxedSequenceModeWarning());
+
+  AppendMuxedCluster(MuxedStreamInfo(kAudioTrackNum, "0D10K"),
+                     MuxedStreamInfo(kVideoTrackNum, "0D10K"));
+}
+
+TEST_F(ChunkDemuxerTest, SequenceModeSingleTrackNoWarning) {
+  std::string audio_id = "audio1";
+  std::string video_id = "video1";
+
+  EXPECT_MEDIA_LOG(MuxedSequenceModeWarning()).Times(0);
+
+  ASSERT_TRUE(InitDemuxerAudioAndVideoSources(audio_id, video_id));
+
+  demuxer_->SetSequenceMode(audio_id, true);
+  demuxer_->SetSequenceMode(video_id, true);
+
+  // Append audio and video data into separate source ids.
+  ASSERT_TRUE(AppendCluster(
+      audio_id, GenerateSingleStreamCluster(0, 23, kAudioTrackNum, 23)));
+  ASSERT_TRUE(AppendCluster(
+      video_id, GenerateSingleStreamCluster(0, 33, kVideoTrackNum, 33)));
+}
+
 TEST_F(ChunkDemuxerTest, Mp4Vp9CodecSupport) {
   ChunkDemuxer::Status expected = ChunkDemuxer::kNotSupported;
 #if BUILDFLAG(USE_PROPRIETARY_CODECS)

filters/frame_processor.cc

@@ -17,6 +17,7 @@ namespace media {
 
 const int kMaxDroppedPrerollWarnings = 10;
 const int kMaxDtsBeyondPtsWarnings = 10;
+const int kMaxMuxedSequenceModeWarnings = 1;
 
 // Helper class to capture per-track details needed by a frame processor. Some
 // of this information may be duplicated in the short-term in the associated
@@ -207,6 +208,16 @@ bool FrameProcessor::ProcessFrames(
 
   DCHECK(!frames.empty());
 
+  if (sequence_mode_ && track_buffers_.size() > 1) {
+    LIMITED_MEDIA_LOG(DEBUG, media_log_, num_muxed_sequence_mode_warnings_,
+                      kMaxMuxedSequenceModeWarnings)
+        << "Warning: using MSE 'sequence' AppendMode for a SourceBuffer with "
+           "multiple tracks may cause loss of track synchronization. In some "
+           "cases, buffered range gaps and playback stalls can occur. It is "
+           "recommended to instead use 'segments' mode for a multitrack "
+           "SourceBuffer.";
+  }
+
   // Implements the coded frame processing algorithm's outer loop for step 1.
   // Note that ProcessFrame() implements an inner loop for a single frame that
   // handles "jump to the Loop Top step to restart processing of the current

filters/frame_processor.h

@@ -175,6 +175,7 @@ class MEDIA_EXPORT FrameProcessor {
   // Counters that limit spam to |media_log_| for frame processor warnings.
   int num_dropped_preroll_warnings_ = 0;
   int num_dts_beyond_pts_warnings_ = 0;
+  int num_muxed_sequence_mode_warnings_ = 0;
 
   DISALLOW_COPY_AND_ASSIGN(FrameProcessor);
 };