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// 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.
#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.
base::TimeDelta Play();
// Stops the clock and returns the current media time, which will remain
// constant until Play() is called.
base::TimeDelta Pause();
// Sets a new playback rate. The rate at which the media time will increase
// will now change.
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).
void SetTime(const base::TimeDelta& time);
// Returns the current elapsed media time.
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_;
DISALLOW_COPY_AND_ASSIGN(Clock);
};
} // namespace media
#endif // MEDIA_BASE_CLOCK_H_
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