Change the TimeSource interface to return wallclock time for video.

media/base/time_source.h

 // Copyright 2014 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_TIME_SOURCE_H_
 #define MEDIA_BASE_TIME_SOURCE_H_
 
 #include "base/time/time.h"
 #include "media/base/media_export.h"
 
@@ skipping 20 matching lines @@
 
   // Sets the media time to start ticking from. Only valid to call while the
   // time source is not ticking.
   virtual void SetMediaTime(base::TimeDelta time) = 0;
 
   // Returns the current media time.
   //
   // Values returned are intended for informational purposes, such as displaying
   // UI with the current minute and second count. While it is guaranteed values
   // will never go backwards, the frequency at which they update may be low.
   virtual base::TimeDelta CurrentMediaTime() = 0;

[xhwang, 2015/03/23 22:20:13]

nit: Since TimeDelta specifies a duration, we probably should make it clear
what's the base time, e.g. since the playback starts.

[DaleCurtis, 2015/03/25 00:31:44]

The current media time is relative to 0?

 
-  // Returns the current media time for use with synchronizing video.
+  // Converts a media timestamp into a wallclock timestamp. If media time is
+  // stopped, returns a null TimeTicks.
   //
-  // Differences from CurrentMediaTime():
-  //   - Values returned update at a much higher frequency (e.g., suitable for
-  //     playback of 60 FPS content).
-  //   - As a result, values may go slightly backwards depending on the
-  //     implementation (e.g., uses interpolation).
-  //
-  // TODO(scherkus): Replace with a method that returns wall clock time for a
-  // given media time for use with VideoFrameScheduler http://crbug.com/110814
-  virtual base::TimeDelta CurrentMediaTimeForSyncingVideo() = 0;
+  // Values too far ahead of or behind the current media time will return an
+  // estimated value; as such, these values may go backwards in time slightly.
+  virtual base::TimeTicks GetWallclockTimeForMediaTime(

[xhwang, 2015/03/23 22:20:13]

s/Wallclock/WallClock/

At least in WallClockTimeSource, we treat wall and clock two separate words.

[xhwang, 2015/03/23 22:20:13]

nit: how about just GetWallClockTime(base::TimeDelta media_time) ?

[DaleCurtis, 2015/03/25 00:31:44]

Done.

+      base::TimeDelta time) = 0;
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_TIME_SOURCE_H_