Implement mapping blink track id to demuxer streams

media/filters/chunk_demuxer_unittest.cc

Index: media/filters/chunk_demuxer_unittest.cc
diff --git a/media/filters/chunk_demuxer_unittest.cc b/media/filters/chunk_demuxer_unittest.cc
index db320ba00e0e5ea5a0afccbcc2b0e2beb0222b25..c1864f7056845af72ab1064fd2f4e24a9168589d 100644
--- a/media/filters/chunk_demuxer_unittest.cc
+++ b/media/filters/chunk_demuxer_unittest.cc
@@ -82,6 +82,8 @@ const int kVideoTrackSizeWidth = 8;
 const int kVideoTrackEntryHeaderSize =
     kVideoTrackSizeOffset + kVideoTrackSizeWidth;
 

[chcunningham, 2016/06/02 21:24:45]

Similar test for ffmpeg_demuxer would be good

[servolk, 2016/06/02 23:53:11]

FFmpeg demuxer currently doesn't support mid-stream config changes, so there's
only one set of tracks that is determined at the beginning of playback and never
changes after that.

+// Track numbers AKA bytestream track ids. Bytestream track ids might change
+// within a single playback session if there is only one track of a given type.
 const int kVideoTrackNum = 1;
 const int kAudioTrackNum = 2;
 const int kTextTrackNum = 3;
@@ -89,6 +91,14 @@ const int kAlternateVideoTrackNum = 4;
 const int kAlternateAudioTrackNum = 5;
 const int kAlternateTextTrackNum = 6;
 
+// These value represent externally assigned track ids (for example track ids
+// assigned by blink). Not to be confused with bytestream track ids above. The
+// main difference is that these track ids must stay the same for the duration
+// of the playback session, whereas track numbers / bytestream track ids might

[chcunningham, 2016/06/02 21:24:45]

I was surprised to read this. Looking at the code here [0] it seems we expect
bytestream track ids to map to blink track ids. And if we encounter a new
bytstream track id, we seem to expect that it is already known (existing) in
SourceBuffer if we've already processed the first init segment? What am I
missing? 

[0]
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

[servolk, 2016/06/02 23:53:11]

That's right. If we encounter a new bytestream track id and there's only one
track of the given type, then we assume that new bytestream track corresponds to
the same track, even if the actual bytestream id is different. So the
external/blink track ids below map to the k*TrackNum in the first init segment
and kAlternate*TrackNum in the second init segment.

[chcunningham, 2016/06/03 20:42:49]

I see. Are we missing some code in SourceBuffer.cpp? IIUC we add tracks with the
original bystream track ids upon receiving the first init segment. But if a
later init segment changes the bytstream track id, we seem to expect to find a
track with that bytstream id already in the track list?

+// change in subsequent init segments.
+const int kVideoTrackId = 10;

[chcunningham, 2016/06/02 21:24:45]

Also, can you name these in a way that describes their different purpose? E.g.
kExternalVideoTrackId vs kBystreamVideoTrackId

[servolk, 2016/06/02 23:53:11]

Done.

+const int kAudioTrackId = 11;
+
 const int kAudioBlockDuration = 23;
 const int kVideoBlockDuration = 33;
 const int kTextBlockDuration = 100;
@@ -1404,6 +1414,18 @@ class ChunkDemuxerTest : public ::testing::Test {
     DCHECK(tracks.get());
     DCHECK_GT(tracks->tracks().size(), 0u);
 

[chcunningham, 2016/06/02 21:24:45]

This is busted for multi-track right? You might assert that you only see one
track of a given type

[servolk, 2016/06/02 23:53:11]

Yes, but there are many other places in Chromium media pipeline where we assume
there's only one audio and one video track (e.g.
DemuxerStreamProvider::GetStream and media::Renderer implementations).

+    std::vector<unsigned> track_ids;
+    for (const auto& track : tracks->tracks()) {
+      if (track->type() == MediaTrack::Audio) {
+        track_ids.push_back(kAudioTrackId);
+      } else if (track->type() == MediaTrack::Video) {
+        track_ids.push_back(kVideoTrackId);
+      } else {
+        NOTREACHED();
+      }
+    }
+    demuxer_->OnTrackIdsAssigned(*tracks.get(), track_ids);
+
     InitSegmentReceivedMock(tracks);
   }
 
@@ -1603,6 +1625,8 @@ TEST_F(ChunkDemuxerTest, AudioVideoTrackIdsChange) {
   DemuxerStream* video_stream = demuxer_->GetStream(DemuxerStream::VIDEO);
   ASSERT_TRUE(audio_stream);
   ASSERT_TRUE(video_stream);
+  ASSERT_EQ(audio_stream, demuxer_->GetDemuxerStreamByTrackId(kAudioTrackId));
+  ASSERT_EQ(video_stream, demuxer_->GetDemuxerStreamByTrackId(kVideoTrackId));
 
   AppendMuxedCluster(MuxedStreamInfo(kAudioTrackNum, "0K 23K", 23),
                      MuxedStreamInfo(kVideoTrackNum, "0K 30", 30));
@@ -1616,6 +1640,8 @@ TEST_F(ChunkDemuxerTest, AudioVideoTrackIdsChange) {
   CheckExpectedRanges("{ [0,92) }");
   CheckExpectedBuffers(audio_stream, "0K 23K 46K 69K");
   CheckExpectedBuffers(video_stream, "0K 30 60K");
+  ASSERT_EQ(audio_stream, demuxer_->GetDemuxerStreamByTrackId(kAudioTrackId));
+  ASSERT_EQ(video_stream, demuxer_->GetDemuxerStreamByTrackId(kVideoTrackId));
 
   ShutdownDemuxer();
 }