New FRAME_DURATION VideoFrameMetadata, with Cast Streaming use case.

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 31fbe74989253c92dab9dd0adc082a8223b2aa2d..f6b5ec25a7ad257b66a879068ecbd81f37d7aa1c 100644
--- a/media/base/video_frame_metadata.h
+++ b/media/base/video_frame_metadata.h
@@ -21,6 +21,11 @@ class MEDIA_EXPORT VideoFrameMetadata {
     CAPTURE_BEGIN_TIME,
     CAPTURE_END_TIME,
 
+    // The estimated duration of this frame (i.e., the amount of time between
+    // the media timestamp of this frame and the next).  Use Get/SetTimeDelta()
+    // for this key.
+    FRAME_DURATION,

[hubbe, 2015/05/19 17:58:32]

I think some additional explanation is needed.
I mean, isn't FRAME_DURATION equal to 1/FRAME_RATE ?

[miu, 2015/05/19 20:14:52]

Done.

+
     // Represents either the fixed frame rate, or the maximum frame rate to
     // expect from a variable-rate source.  Use Get/SetDouble() for this key.
     FRAME_RATE,
@@ -40,6 +45,7 @@ class MEDIA_EXPORT VideoFrameMetadata {
   void SetInteger(Key key, int value);
   void SetDouble(Key key, double value);
   void SetString(Key key, const std::string& value);
+  void SetTimeDelta(Key key, const base::TimeDelta& value);
   void SetTimeTicks(Key key, const base::TimeTicks& value);
   void SetValue(Key key, scoped_ptr<base::Value> value);
 
@@ -48,6 +54,7 @@ class MEDIA_EXPORT VideoFrameMetadata {
   bool GetInteger(Key key, int* value) const WARN_UNUSED_RESULT;
   bool GetDouble(Key key, double* value) const WARN_UNUSED_RESULT;
   bool GetString(Key key, std::string* value) const WARN_UNUSED_RESULT;
+  bool GetTimeDelta(Key key, base::TimeDelta* value) const WARN_UNUSED_RESULT;
   bool GetTimeTicks(Key key, base::TimeTicks* value) const WARN_UNUSED_RESULT;
 
   // Returns null if |key| was not present.