Base A/V synchronization on sync_labels.

webrtc/video_receive_stream.h

Index: webrtc/video_receive_stream.h
diff --git a/webrtc/video_receive_stream.h b/webrtc/video_receive_stream.h
index 5e5ece5a2004f691b2b806bd1d000198d9ce2e5f..f4d059fc8a15af041f238534d5b7be1f6feb5c42 100644
--- a/webrtc/video_receive_stream.h
+++ b/webrtc/video_receive_stream.h
@@ -93,7 +93,6 @@ class VideoReceiveStream {
     Config()
         : renderer(NULL),
           render_delay_ms(10),
-          audio_channel_id(-1),
           pre_decode_callback(NULL),
           pre_render_callback(NULL),
           target_delay_ms(0) {}
@@ -166,10 +165,10 @@ class VideoReceiveStream {
     // Only valid if 'renderer' is set.
     int render_delay_ms;
 
-    // Audio channel corresponding to this video stream, used for audio/video
-    // synchronization. 'audio_channel_id' is ignored if no VoiceEngine is set
-    // when creating the VideoEngine instance. '-1' disables a/v sync.
-    int audio_channel_id;
+    // Identifier for an A/V synchronization group. Empty string to disable.
+    // TODO(pbos): Synchronize streams in a sync group, not just video streams
+    // to one of the audio streams.
+    std::string sync_group;
 
     // Called for each incoming video frame, i.e. in encoded state. E.g. used
     // when