Base A/V synchronization on sync_labels.

webrtc/video_receive_stream.h

 /*
  *  Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 127 matching lines @@
 
     // VideoRenderer will be called for each decoded frame. 'nullptr' disables
     // rendering of this stream.
     VideoRenderer* renderer = nullptr;
 
     // Expected delay needed by the renderer, i.e. the frame will be delivered
     // this many milliseconds, if possible, earlier than the ideal render time.
     // Only valid if 'renderer' is set.
     int render_delay_ms = 10;
 
-    // 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 = -1;
+    // 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
     // saving the stream to a file. 'nullptr' disables the callback.
     EncodedFrameObserver* pre_decode_callback = nullptr;
 
     // Called for each decoded frame. E.g. used when adding effects to the
     // decoded
     // stream. 'nullptr' disables the callback.
     I420FrameCallback* pre_render_callback = nullptr;
 
     // Target delay in milliseconds. A positive value indicates this stream is
     // used for streaming instead of a real-time call.
     int target_delay_ms = 0;
   };
 
   virtual void Start() = 0;
   virtual void Stop() = 0;
 
   // TODO(pbos): Add info on currently-received codec to Stats.
   virtual Stats GetStats() const = 0;
 
  protected:
   virtual ~VideoReceiveStream() {}
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_VIDEO_RECEIVE_STREAM_H_