Cast: deliver video frames on the IO thread

content/public/renderer/media_stream_video_sink.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_PUBLIC_RENDERER_MEDIA_STREAM_VIDEO_SINK_H_
 #define CONTENT_PUBLIC_RENDERER_MEDIA_STREAM_VIDEO_SINK_H_
 
+#include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/memory/ref_counted.h"
 #include "content/common/content_export.h"
 #include "content/public/renderer/media_stream_sink.h"
 
 namespace media {
+class VideoCaptureFormat;
 class VideoFrame;
 }
 
 namespace blink {
 class WebMediaStreamTrack;
 }
 
 namespace content {
 
+typedef base::Callback<
+  void(const scoped_refptr<media::VideoFrame>&,
+       const media::VideoCaptureFormat&)>
+    VideoSinkDeliverFrameCB;
+
 // MediaStreamVideoSink is an interface used for receiving video frames from a
 // Video Stream Track or a Video Source.
 // http://dev.w3.org/2011/webrtc/editor/getusermedia.html
 // All methods calls will be done from the main render thread.
 class CONTENT_EXPORT MediaStreamVideoSink : public MediaStreamSink {
  public:
   // An implementation of MediaStreamVideoSink should call AddToVideoTrack when
   // it is ready to receive data from a video track. Before the implementation
   // is destroyed, RemoveFromVideoTrack must be called.
+  //
   // Calls to these methods must be done on the main render thread.
+  // Note that |callback| for frame delivery happens on the IO thread.
+  //
+  // Calling RemoveFromVideoTrack also not stop frame delivery through the
+  // callback immediately because it may happen on another thread.
+  // The added callback will be reset on the render thread.
   static void AddToVideoTrack(MediaStreamVideoSink* sink,
+                              const VideoSinkDeliverFrameCB& callback,
                               const blink::WebMediaStreamTrack& track);
   static void RemoveFromVideoTrack(MediaStreamVideoSink* sink,
                                    const blink::WebMediaStreamTrack& track);
 
-  virtual void OnVideoFrame(const scoped_refptr<media::VideoFrame>& frame) = 0;
-
  protected:
   virtual ~MediaStreamVideoSink() {}
 };
 
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_RENDERER_MEDIA_STREAM_VIDEO_SINK_H_