Generate and assign media track ids in demuxers.

media/filters/media_source_state.cc

Index: media/filters/media_source_state.cc
diff --git a/media/filters/media_source_state.cc b/media/filters/media_source_state.cc
index 6a1d95f6190f3369ab66db489c948abcafade5d1..b3cf09efcad17bc79f12e3df5634e25c70ddaf26 100644
--- a/media/filters/media_source_state.cc
+++ b/media/filters/media_source_state.cc
@@ -151,8 +151,8 @@ void MediaSourceState::SetGroupStartTimestampIfInSequenceMode(
 void MediaSourceState::SetTracksWatcher(
     const Demuxer::MediaTracksUpdatedCB& tracks_updated_cb) {
   DCHECK(init_segment_received_cb_.is_null());
+  DCHECK(!tracks_updated_cb.is_null());
   init_segment_received_cb_ = tracks_updated_cb;
-  DCHECK(!init_segment_received_cb_.is_null());
 }
 
 bool MediaSourceState::Append(const uint8_t* data,
@@ -481,9 +481,22 @@ bool MediaSourceState::OnNewConfigs(
   DCHECK_GE(state_, PENDING_PARSER_CONFIG);
   DCHECK(tracks.get());
 
-  media_tracks_ = std::move(tracks);
-  const AudioDecoderConfig& audio_config = media_tracks_->getFirstAudioConfig();
-  const VideoDecoderConfig& video_config = media_tracks_->getFirstVideoConfig();
+  MediaTrack* audio_track = nullptr;
+  MediaTrack* video_track = nullptr;
+  AudioDecoderConfig audio_config;
+  VideoDecoderConfig video_config;
+  for (const auto& track : tracks->tracks()) {

[xhwang, 2016/06/10 17:06:54]

So if we have multiple audio (or video) tracks, we'll only use the first audio
(or video) one. Maybe add a comment about this behavior.

+    const auto& track_id = track->bytestream_track_id();

[xhwang, 2016/06/10 17:06:54]

nit: It's really hard to follow that whether a |track_id| is a
bytestream_track_id, or a MediaTrack:Id... See my comment above about the
possibility to improve naming.

+    if (!audio_track && track->type() == MediaTrack::Audio &&
+        tracks->getAudioConfig(track_id).IsValidConfig()) {
+      audio_config = tracks->getAudioConfig(track_id);
+      audio_track = track.get();
+    } else if (!video_track && track->type() == MediaTrack::Video &&
+               tracks->getVideoConfig(track_id).IsValidConfig()) {
+      video_config = tracks->getVideoConfig(track_id);
+      video_track = track.get();
+    }
+  }
 
   DVLOG(1) << "OnNewConfigs(" << allow_audio << ", " << allow_video << ", "
            << audio_config.IsValidConfig() << ", "
@@ -652,12 +665,21 @@ bool MediaSourceState::OnNewConfigs(
 
   frame_processor_->SetAllTrackBuffersNeedRandomAccessPoint();
 
+  if (audio_track) {
+    DCHECK(audio_);
+    audio_track->set_id(audio_->media_track_id());
+  }
+  if (video_track) {
+    DCHECK(video_);
+    video_track->set_id(video_->media_track_id());
+  }
+
   DVLOG(1) << "OnNewConfigs() : " << (success ? "success" : "failed");
   if (success) {
     if (state_ == PENDING_PARSER_CONFIG)
       state_ = PENDING_PARSER_INIT;
     DCHECK(!init_segment_received_cb_.is_null());
-    init_segment_received_cb_.Run(std::move(media_tracks_));
+    init_segment_received_cb_.Run(std::move(tracks));
   }
 
   return success;