Implemented a proper clock for audio/video synchronization.

media/base/clock_impl.h

+// Copyright (c) 2009 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.
+//
+// An implementation of Clock based on the system clock.  ClockImpl uses linear
+// interpolation to calculate the current media time since the last time
+// SetTime() was called.
+//
+// ClockImpl is not thread-safe and must be externally locked.
+
+#ifndef MEDIA_BASE_CLOCK_IMPL_H_
+#define MEDIA_BASE_CLOCK_IMPL_H_
+
+#include "media/base/clock.h"
+
+namespace media {
+
+// Type for a static function pointer that acts as a time source.
+typedef base::Time(TimeProvider)();
+
+class ClockImpl : public Clock {
+ public:
+  ClockImpl(TimeProvider* time_provider);
+  virtual ~ClockImpl();
+
+  // Clock implementation.
+  virtual base::TimeDelta Play();
+  virtual base::TimeDelta Pause();
+  virtual void SetPlaybackRate(float playback_rate);
+  virtual void SetTime(const base::TimeDelta& time);
+  virtual 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;
+
+  // 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_;
+
+  DISALLOW_COPY_AND_ASSIGN(ClockImpl);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_CLOCK_IMPL_H_