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// Copyright (c) 2012 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/basictypes.h"
#include "base/time/time.h"
#include "media/base/media_export.h"
namespace base {
class TickClock;
} // namespace base
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 monotonic
// 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.
//
// TODO(miu): Rename media::Clock to avoid confusion (and tripping up the media
// PRESUBMIT script on future changes).
class MEDIA_EXPORT Clock {
public:
explicit Clock(base::TickClock* clock);
~Clock();
// Returns true if the clock is running.
bool IsPlaying() const;
// 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 |current_time|. The second parameter is
// the |max_time| that the clock should progress after a call to Play(). This
// value is often the time of the end of the last frame buffered and decoded.
//
// These values are clamped to the duration of the video, which is initially
// set to 0 (before SetDuration() is called).
void SetTime(base::TimeDelta current_time, base::TimeDelta max_time);
// Sets the |max_time| to be returned by a call to Elapsed().
void SetMaxTime(base::TimeDelta max_time);
// Returns the current elapsed media time. Returns 0 if SetDuration() has
// never been called.
base::TimeDelta Elapsed();
// Sets the duration of the video. Clock expects the duration will be set
// exactly once.
void SetDuration(base::TimeDelta duration);
// Returns the duration of the clock, or 0 if not set.
base::TimeDelta Duration() const;
private:
// Updates the reference points based on the current calculated time.
void UpdateReferencePoints();
// Updates the reference points based on the given |current_time|.
void UpdateReferencePoints(base::TimeDelta current_time);
// Returns the time elapsed based on the current reference points, ignoring
// the |max_time_| cap.
base::TimeDelta EstimatedElapsedTime();
// Translates |time| into the current media time, based on the perspective of
// the monotonically-increasing system clock.
base::TimeDelta ElapsedViaProvidedTime(const base::TimeTicks& time) const;
base::TimeDelta ClampToValidTimeRange(base::TimeDelta time) const;
base::TickClock* const clock_;
// Whether the clock is running.
bool playing_;
// Whether the clock is stalled because it has reached the |max_time_|
// allowed.
bool underflow_;
// The monotonic system clock time when this Clock last started playing or had
// its time set via SetTime().
base::TimeTicks 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_;
// The maximum time that can be returned by calls to Elapsed().
base::TimeDelta max_time_;
// Duration of the media.
base::TimeDelta duration_;
DISALLOW_COPY_AND_ASSIGN(Clock);
};
} // namespace media
#endif // MEDIA_BASE_CLOCK_H_
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