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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_AUDIO_TIMESTAMP_HELPER_H_
#define MEDIA_BASE_AUDIO_TIMESTAMP_HELPER_H_
#include "base/time/time.h"
#include "media/base/media_export.h"
namespace media {
// Generates timestamps for a sequence of audio sample frames. This class should
// be used any place timestamps need to be calculated for a sequence of audio
// samples. It helps avoid timestamps inaccuracies caused by rounding/truncation
// in repeated sample count to timestamp conversions.
//
// The class is constructed with samples_per_second information so that it can
// convert audio sample frame counts into timestamps. After the object is
// constructed, SetBaseTimestamp() must be called to specify the starting
// timestamp of the audio sequence. As audio samples are received, their frame
// counts are added using AddFrames(). These frame counts are accumulated by
// this class so GetTimestamp() can be used to determine the timestamp for the
// samples that have been added. GetDuration() calculates the proper duration
// values for samples added to the current timestamp. GetFramesToTarget()
// determines the number of frames that need to be added/removed from the
// accumulated frames to reach a target timestamp.
class MEDIA_EXPORT AudioTimestampHelper {
public:
explicit AudioTimestampHelper(int samples_per_second);
// Sets the base timestamp to |base_timestamp| and the sets count to 0.
void SetBaseTimestamp(base::TimeDelta base_timestamp);
base::TimeDelta base_timestamp() const;
int64 frame_count() const { return frame_count_; }
// Adds |frame_count| to the frame counter.
// Note: SetBaseTimestamp() must be called with a value other than
// kNoTimestamp() before this method can be called.
void AddFrames(int frame_count);
// Get the current timestamp. This value is computed from the base_timestamp()
// and the number of sample frames that have been added so far.
base::TimeDelta GetTimestamp() const;
// Gets the duration if |frame_count| frames were added to the current
// timestamp reported by GetTimestamp(). This method ensures that
// (GetTimestamp() + GetFrameDuration(n)) will equal the timestamp that
// GetTimestamp() will return if AddFrames(n) is called.
base::TimeDelta GetFrameDuration(int frame_count) const;
// Returns the number of frames needed to reach the target timestamp.
// Note: |target| must be >= |base_timestamp_|.
int64 GetFramesToTarget(base::TimeDelta target) const;
private:
base::TimeDelta ComputeTimestamp(int64 frame_count) const;
double microseconds_per_frame_;
base::TimeDelta base_timestamp_;
// Number of frames accumulated by AddFrames() calls.
int64 frame_count_;
DISALLOW_IMPLICIT_CONSTRUCTORS(AudioTimestampHelper);
};
} // namespace media
#endif
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