Base A/V synchronization on sync_labels.

talk/media/webrtc/webrtcvideoengine2.cc

 /*
  * libjingle
  * Copyright 2014 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
  *
  *  1. Redistributions of source code must retain the above copyright notice,
  *     this list of conditions and the following disclaimer.
  *  2. Redistributions in binary form must reproduce the above copyright notice,
@@ skipping 1137 matching lines @@
 
   if (!ValidateReceiveSsrcAvailability(sp))
     return false;
 
   for (uint32 used_ssrc : sp.ssrcs)
     receive_ssrcs_.insert(used_ssrc);
 
   webrtc::VideoReceiveStream::Config config;
   ConfigureReceiverRtp(&config, sp);
 
-  // Set up A/V sync if there is a VoiceChannel.
-  // TODO(pbos): The A/V is synched by the receiving channel. So we need to know
-  // the SSRC of the remote audio channel in order to sync the correct webrtc
-  // VoiceEngine channel. For now sync the first channel in non-conference to
-  // match existing behavior in WebRtcVideoEngine.
-  if (voice_channel_id_ != -1 && receive_streams_.empty() &&
-      !options_.conference_mode.GetWithDefaultIfUnset(false)) {
-    config.audio_channel_id = voice_channel_id_;
-  }
+  // Set up A/V sync group based on sync label.
+  config.sync_group = sp.sync_label;
 
   config.rtp.remb = false;
   VideoCodecSettings send_codec;
   if (send_codec_.Get(&send_codec)) {
     config.rtp.remb = HasRemb(send_codec.codec);
   }
 
   receive_streams_[ssrc] = new WebRtcVideoReceiveStream(
       call_.get(), sp, external_decoder_factory_, default_stream, config,
       recv_codecs_);
@@ skipping 1433 matching lines @@
       video_codecs[i].rtx_payload_type = rtx_mapping[video_codecs[i].codec.id];
     }
   }
 
   return video_codecs;
 }
 
 }  // namespace cricket
 
 #endif  // HAVE_WEBRTC_VIDEO