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..55adf2a682c2d9308e7dd892fe4cfaea6bd34862 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;
 
+// 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
+// change in subsequent init segments.
+const int kExternalVideoTrackId = 10;
+const int kExternalAudioTrackId = 11;
+
 const int kAudioBlockDuration = 23;
 const int kVideoBlockDuration = 33;
 const int kTextBlockDuration = 100;
@@ -1404,6 +1414,24 @@ class ChunkDemuxerTest : public ::testing::Test {
     DCHECK(tracks.get());
     DCHECK_GT(tracks->tracks().size(), 0u);
 
+    std::vector<unsigned> track_ids;
+    bool found_audio_track = false;
+    bool found_video_track = false;
+    for (const auto& track : tracks->tracks()) {
+      if (track->type() == MediaTrack::Audio) {
+        DCHECK(!found_audio_track);
+        found_audio_track = true;
+        track_ids.push_back(kExternalAudioTrackId);
+      } else if (track->type() == MediaTrack::Video) {
+        DCHECK(!found_video_track);
+        found_video_track = true;
+        track_ids.push_back(kExternalVideoTrackId);
+      } else {
+        NOTREACHED();
+      }
+    }
+    demuxer_->OnTrackIdsAssigned(*tracks.get(), track_ids);
+
     InitSegmentReceivedMock(tracks);
   }
 
@@ -1603,6 +1631,10 @@ 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(kExternalAudioTrackId));
+  ASSERT_EQ(video_stream,
+            demuxer_->GetDemuxerStreamByTrackId(kExternalVideoTrackId));
 
   AppendMuxedCluster(MuxedStreamInfo(kAudioTrackNum, "0K 23K", 23),
                      MuxedStreamInfo(kVideoTrackNum, "0K 30", 30));
@@ -1616,6 +1648,10 @@ 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(kExternalAudioTrackId));
+  ASSERT_EQ(video_stream,
+            demuxer_->GetDemuxerStreamByTrackId(kExternalVideoTrackId));
 
   ShutdownDemuxer();
 }