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// Copyright 2014 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_TIME_SOURCE_H_
#define MEDIA_BASE_TIME_SOURCE_H_
#include "base/time/time.h"
#include "media/base/media_export.h"
namespace media {
// A TimeSource is capable of providing the current media time.
class MEDIA_EXPORT TimeSource {
public:
TimeSource() {}
virtual ~TimeSource() {}
// Signal the time source to start ticking. It is expected that values from
// CurrentMediaTime() will start increasing.
virtual void StartTicking() = 0;
// Signal the time source to stop ticking. It is expected that values from
// CurrentMediaTime() will remain constant.
virtual void StopTicking() = 0;
// Updates the current playback rate. It is expected that values from
// CurrentMediaTime() will eventually reflect the new playback rate (e.g., the
// media time will advance at half speed if the rate was set to 0.5f).
virtual void SetPlaybackRate(double playback_rate) = 0;
// Sets the media time to start ticking from. Only valid to call while the
// time source is not ticking.
virtual void SetMediaTime(base::TimeDelta time) = 0;
// Returns the current media timestamp relative to the timestamp set by
// SetMediaTime().
//
// Values returned are intended for informational purposes, such as displaying
// UI with the current minute and second count. While it is guaranteed values
// will never go backwards, the frequency at which they update may be low.
virtual base::TimeDelta CurrentMediaTime() = 0;
// Converts a media timestamp into a wall clock time. If the media time is
// stopped, returns a null TimeTicks.
//
// |media_time| values too far ahead of the current media time will return an
// estimated value; as such, these values may go backwards in time slightly.
//
// |media_time| values behind the current media time may be significantly
// incorrect if the playback rate has changed recently. The only guarantee is
// that the returned time will be less than the current wall clock time.
virtual base::TimeTicks GetWallClockTime(base::TimeDelta media_time) = 0;
};
} // namespace media
#endif // MEDIA_BASE_TIME_SOURCE_H_
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