1 files changed, 51 insertions, 21 deletions

diff --git a/media/base/clock.h b/media/base/clock.h
index 52f3d8a..df94cad 100644
--- a/media/base/clock.h
+++ b/media/base/clock.h
@@ -1,51 +1,81 @@
-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 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.
-//
-// A clock represent a single source of time to allow audio and video streams
-// to synchronize with each other.  Clocks essentially track the media time with
-// respect to some other source of time, whether that may be the system clock,
-// audio hardware or some other OS-level API.
-//
-// Clocks start off paused with a playback rate of 1.0f and a media time of 0.
-//
-// TODO(scherkus): Clocks will some day be responsible for executing callbacks
-// given a media time.  This will be used primarily by video renderers.  For now
-// we'll keep using a poll-and-sleep solution.
 
 #ifndef MEDIA_BASE_CLOCK_H_
 #define MEDIA_BASE_CLOCK_H_
 
+#include "base/gtest_prod_util.h"
 #include "base/scoped_ptr.h"
 #include "base/time.h"
 
 namespace media {
 
+// A clock represents a single source of time to allow audio and video streams
+// to synchronize with each other.  Clock essentially tracks the media time with
+// respect to some other source of time, whether that may be the system clock or
+// updates via SetTime(). Clock uses linear interpolation to calculate the
+// current media time since the last time SetTime() was called.
+//
+// Clocks start off paused with a playback rate of 1.0f and a media time of 0.
+//
+// Clock is not thread-safe and must be externally locked.
+//
+// TODO(scherkus): Clock will some day be responsible for executing callbacks
+// given a media time.  This will be used primarily by video renderers.  For now
+// we'll keep using a poll-and-sleep solution.
 class Clock {
  public:
+  // Type for a static function pointer that acts as a time source.
+  typedef base::Time(TimeProvider)();
+
+  Clock(TimeProvider* time_provider);
+  ~Clock();
+
   // Starts the clock and returns the current media time, which will increase
   // with respect to the current playback rate.
-  virtual base::TimeDelta Play() = 0;
+  base::TimeDelta Play();
 
   // Stops the clock and returns the current media time, which will remain
   // constant until Play() is called.
-  virtual base::TimeDelta Pause() = 0;
+  base::TimeDelta Pause();
 
   // Sets a new playback rate.  The rate at which the media time will increase
   // will now change.
-  virtual void SetPlaybackRate(float playback_rate) = 0;
+  void SetPlaybackRate(float playback_rate);
 
   // Forcefully sets the media time to the given time.  This should only be used
   // where a discontinuity in the media is found (i.e., seeking).
-  virtual void SetTime(const base::TimeDelta& time) = 0;
+  void SetTime(const base::TimeDelta& time);
 
   // Returns the current elapsed media time.
-  virtual base::TimeDelta Elapsed() const = 0;
+  base::TimeDelta Elapsed() const;
+
+ private:
+  // Returns the current media time treating the given time as the latest
+  // value as returned by |time_provider_|.
+  base::TimeDelta ElapsedViaProvidedTime(const base::Time& time) const;
+
+  base::Time GetTimeFromProvider() const;
+
+  // Function returning current time in base::Time units.
+  TimeProvider* time_provider_;
+
+  // Whether the clock is running.
+  bool playing_;
+
+  // The system clock time when this clock last starting playing or had its
+  // time set via SetTime().
+  base::Time reference_;
+
+  // Current accumulated amount of media time.  The remaining portion must be
+  // calculated by comparing the system time to the reference time.
+  base::TimeDelta media_time_;
+
+  // Current playback rate.
+  float playback_rate_;
 
- protected:
-  // Only allow scoped_ptr<> to delete clocks.
-  friend class scoped_ptr<Clock>;
-  virtual ~Clock() {}
+  DISALLOW_COPY_AND_ASSIGN(Clock);
 };
 
 }  // namespace media