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"
+#include "media/video/capture/video_capture_types.h"

[perkj_chrome, 2014/05/08 08:15:08]

 Can you forward declare const media::VideoCaptureFormat& the same way as
VideoFrame instead.

[Alpha Left Google, 2014/05/08 18:45:51]

Done.

 
 namespace media {
 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 can be called on an arbitrary

[perkj_chrome, 2014/05/08 08:15:08]

I like not making promises, but I think Tommmi wanted us to guarantee this is on
specific thread, namely the IO-thread currently. 

[Alpha Left Google, 2014/05/08 18:45:51]

Done.

+  // thread. Calling RemoveFromVideoTrack also does not stop frame delivery
+  // through the callback immediately because it may happen on another 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_