New FRAME_DURATION VideoFrameMetadata, with Cast Streaming use case.

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"
 #include "media/base/media_export.h"
 
 namespace media {
 
 class MEDIA_EXPORT VideoFrameMetadata {
  public:
   enum Key {
     // Video capture begin/end timestamps.  Consumers can use these values for
     // dynamic optimizations, logging stats, etc.  Use Get/SetTimeTicks() for
     // these keys.
     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).  Note that this is not
+    // the same information provided by FRAME_RATE as the FRAME_DURATION can
+    // vary unpredictably for every frame.  Consumers can use this to optimize
+    // playback scheduling, make encoding quality decisions, and/or compute
+    // frame-level resource utilization stats.  Use Get/SetTimeDelta() for this
+    // key.
+    FRAME_DURATION,
+
     // Represents either the fixed frame rate, or the maximum frame rate to
-    // expect from a variable-rate source.  Use Get/SetDouble() for this key.
+    // expect from a variable-rate source.  This value generally remains the
+    // same for all frames in the same session.  Use Get/SetDouble() for this
+    // key.
     FRAME_RATE,
 
     NUM_KEYS
   };
 
   VideoFrameMetadata();
   ~VideoFrameMetadata();
 
   bool HasKey(Key key) const;
 
   void Clear() { dictionary_.Clear(); }
 
   // Setters.  Overwrites existing value, if present.
   void SetBoolean(Key key, bool value);
   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);
 
   // Getters.  Returns true if |key| was present and has the value has been set.
   bool GetBoolean(Key key, bool* value) const WARN_UNUSED_RESULT;
   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.
   const base::Value* GetValue(Key key) const WARN_UNUSED_RESULT;
 
   // For serialization.
   void MergeInternalValuesInto(base::DictionaryValue* out) const;
   void MergeInternalValuesFrom(const base::DictionaryValue& in);
 
  private:
   const base::BinaryValue* GetBinaryValue(Key key) const;
 
   base::DictionaryValue dictionary_;
 
   DISALLOW_COPY_AND_ASSIGN(VideoFrameMetadata);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_VIDEO_FRAME_METADATA_H_