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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_DELTA_INTERPOLATOR_H_
#define MEDIA_BASE_TIME_DELTA_INTERPOLATOR_H_
#include "base/basictypes.h"
#include "base/time/time.h"
#include "media/base/media_export.h"
namespace base {
class TickClock;
} // namespace base
namespace media {
// Interpolates between two TimeDeltas based on the passage of wall clock time
// and the current playback rate.
//
// TimeDeltaInterpolator is not thread-safe and must be externally locked.
class MEDIA_EXPORT TimeDeltaInterpolator {
public:
// Constructs an interpolator initialized to zero with a rate of 1.0.
//
// |tick_clock| is used for sampling wall clock time for interpolating.
explicit TimeDeltaInterpolator(base::TickClock* tick_clock);
~TimeDeltaInterpolator();
bool interpolating() { return interpolating_; }
// Starts returning interpolated TimeDelta values.
//
// |tick_clock| will be queried for a new reference time value.
base::TimeDelta StartInterpolating();
// Stops returning interpolated TimeDelta values.
//
// |tick_clock| will be queried for a new reference time value.
base::TimeDelta StopInterpolating();
// Sets a new rate at which to interpolate.
//
// |tick_clock| will be queried for a new reference time value.
void SetPlaybackRate(float playback_rate);
// Sets the two timestamps to interpolate between at |playback_rate_|.
// |upper_bound| must be greater or equal to |lower_bound|.
//
// |upper_bound| is typically the media timestamp of the last audio frame
// buffered by the audio hardware.
void SetBounds(base::TimeDelta lower_bound, base::TimeDelta upper_bound);
// Sets the upper bound used for interpolation. Note that if |upper_bound| is
// less than what was previously set via SetTime(), then all future calls
// to GetInterpolatedTime() will return |upper_bound|.
void SetUpperBound(base::TimeDelta upper_bound);
// Computes an interpolated time based on SetTime().
base::TimeDelta GetInterpolatedTime();
private:
base::TickClock* const tick_clock_;
bool interpolating_;
// The range of time to interpolate between.
base::TimeDelta lower_bound_;
base::TimeDelta upper_bound_;
// The monotonic system clock time used for interpolating between
// |lower_bound_| and |upper_bound_|.
base::TimeTicks reference_;
float playback_rate_;
DISALLOW_COPY_AND_ASSIGN(TimeDeltaInterpolator);
};
} // namespace media
#endif // MEDIA_BASE_TIME_DELTA_INTERPOLATOR_H_
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