Preliminary change for new rtc rendering algorithm

media/base/video_frame_metadata.h

 // Copyright 2015 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 MEDIA_BASE_VIDEO_FRAME_METADATA_H_
 #define MEDIA_BASE_VIDEO_FRAME_METADATA_H_
 
 #include "base/compiler_specific.h"
 #include "base/time/time.h"
 #include "base/values.h"
@@ skipping 50 matching lines @@
     // maximum sustainable utilization.  Greater than 1.0 indicates the consumer
     // is likely to stall or drop frames if the data volume is not reduced.
     //
     // Example: In a system that encodes and transmits video frames over the
     // network, this value can be used to indicate whether sufficient CPU
     // is available for encoding and/or sufficient bandwidth is available for
     // transmission over the network.  The maximum of the two utilization
     // measurements would be used as feedback.
     RESOURCE_UTILIZATION,
 
+    // Render side: a TimeTicks that records the ideal time instant to render

[miu, 2015/08/04 04:35:08]

As this concept is confusing to a lot of media developers, can you provide more
detail?  FWIW, you could pretty much copy-and-paste the comment from here (with
minor changes):
https://code.google.com/p/chromium/codesearch#chromium/src/media/base/video_c...

[qiangchen, 2015/08/04 16:35:25]

Done.

+    // the current frame.
+    // Capture side: a TimeTicks that records the capture time.
+    REFERENCE_TIME,

[miu, 2015/08/04 04:35:08]

Please move this up (for alphabetizing).

[qiangchen, 2015/08/04 16:35:25]

Done.

+
+    // A TimeDelta measuring the time between the current frame and the first
+    // frame of the stream.
+    // TODO(qiangchen): Move VideoFrame::timestamp() to this KEY.
+    ELAPSED_TIME,

[miu, 2015/08/04 04:35:08]

Let's not add ELAPSED_TIME yet.  We can do that in a future change, if we decide
to move VideoFrame::timestamp() into the metadata.

[qiangchen, 2015/08/04 16:35:25]

Done.

+
     NUM_KEYS
   };
 
   VideoFrameMetadata();
   ~VideoFrameMetadata();
 
   bool HasKey(Key key) const;
 
   void Clear() { dictionary_.Clear(); }
 
@@ skipping 28 matching lines @@
   const base::BinaryValue* GetBinaryValue(Key key) const;
 
   base::DictionaryValue dictionary_;
 
   DISALLOW_COPY_AND_ASSIGN(VideoFrameMetadata);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_VIDEO_FRAME_METADATA_H_