Pass a TimeTicks along video capture pipeline to represent capture time

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 "base/time/time.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&)>
+       const media::VideoCaptureFormat&,
+       const base::TimeTicks& start_ticks)>

[Ami GONE FROM CHROMIUM, 2014/05/19 19:01:46]

doco this is the stream start time.

[miu, 2014/05/19 21:59:37]

Throughout this patch: Why must we pass this value with every frame deliver
callback?  It's redundant and wasteful.  Instead, we should have a separate
callback that is only invoked once, just before the first frame, to provide the
start_time.

This would also solve a second problem throughout this patch: There are a lot of
places where you just shove a "null" TimeTicks in when invoking the delivery
callback.  With my suggestion, those implementations that do not support
providing a start_time, would simply never call the
"ProvideStartTimeTicksCallback."

I know this is extra plumbing work, but we should strive to maintain clean,
simple interfaces (which helps us write clean, simple implementations).  We've
been asking this of the WebRTC folks as they clean-up the code in
chrome/renderer/media, so we should be good citizens and do the same.

     VideoSinkDeliverFrameCB;

[Ami GONE FROM CHROMIUM, 2014/05/19 22:14:16]

Is it easy to see why VideoSinkDeliverFrameCB and VideoCaptureDeliverFrameCB
should not be the same typedef?

[Alpha Left Google, 2014/05/31 00:34:50]

I have moved the VideoCaptureDeliverFrameCB to this file to eliminate the
duplication.

 
 // 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.
@@ skipping 11 matching lines @@
                                    const blink::WebMediaStreamTrack& track);
 
  protected:
   virtual ~MediaStreamVideoSink() {}
 };
 
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_RENDERER_MEDIA_STREAM_VIDEO_SINK_H_