Preliminary change for new rtc rendering algorithm

media/base/video_frame_metadata.h

Index: media/base/video_frame_metadata.h
diff --git a/media/base/video_frame_metadata.h b/media/base/video_frame_metadata.h
index bd330f0ed3bfa598ded89b9cc9915a58e7405ca0..86f36cf4447592d2d4a929d3e0696ccefeea1601 100644
--- a/media/base/video_frame_metadata.h
+++ b/media/base/video_frame_metadata.h
@@ -50,6 +50,11 @@ class MEDIA_EXPORT VideoFrameMetadata {
     // key.
     FRAME_RATE,
 
+    // This field represents the local time at which either: 1) the frame was
+    // generated, if it was done so locally; or 2) the targeted play-out time
+    // of the frame, if it was generated from a remote source.

[miu, 2015/08/04 20:37:32]

Please also add: "This value is NOT a high-resolution timestamp, and so it
should not be used as a presentation time; but, instead, it should be used for
buffering playback and for A/V synchronization purposes."

[qiangchen, 2015/08/04 20:56:13]

Done.

+    REFERENCE_TIME,

[miu, 2015/08/04 20:38:19]

Oh, also please mention "Use Get/SetTimeTicks() for this key." as we do for the
other enums here.

[qiangchen, 2015/08/04 20:56:13]

Done.

+
     // A feedback signal that indicates the fraction of the tolerable maximum
     // amount of resources that were utilized to process this frame.  A producer
     // can check this value after-the-fact, usually via a VideoFrame destruction