73 lines
2.9 KiB
C
73 lines
2.9 KiB
C
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// Copyright (c) 2012 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef MEDIA_BASE_AUDIO_TIMESTAMP_HELPER_H_
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#define MEDIA_BASE_AUDIO_TIMESTAMP_HELPER_H_
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#include "base/time/time.h"
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#include "media/base/media_export.h"
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namespace media {
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// Generates timestamps for a sequence of audio sample frames. This class should
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// be used any place timestamps need to be calculated for a sequence of audio
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// samples. It helps avoid timestamps inaccuracies caused by rounding/truncation
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// in repeated sample count to timestamp conversions.
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//
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// The class is constructed with samples_per_second information so that it can
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// convert audio sample frame counts into timestamps. After the object is
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// constructed, SetBaseTimestamp() must be called to specify the starting
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// timestamp of the audio sequence. As audio samples are received, their frame
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// counts are added using AddFrames(). These frame counts are accumulated by
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// this class so GetTimestamp() can be used to determine the timestamp for the
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// samples that have been added. GetDuration() calculates the proper duration
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// values for samples added to the current timestamp. GetFramesToTarget()
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// determines the number of frames that need to be added/removed from the
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// accumulated frames to reach a target timestamp.
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class MEDIA_EXPORT AudioTimestampHelper {
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public:
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explicit AudioTimestampHelper(int samples_per_second);
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// Sets the base timestamp to |base_timestamp| and the sets count to 0.
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void SetBaseTimestamp(base::TimeDelta base_timestamp);
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base::TimeDelta base_timestamp() const;
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int64 frame_count() const { return frame_count_; }
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// Adds |frame_count| to the frame counter.
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// Note: SetBaseTimestamp() must be called with a value other than
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// kNoTimestamp() before this method can be called.
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void AddFrames(int frame_count);
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// Get the current timestamp. This value is computed from the base_timestamp()
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// and the number of sample frames that have been added so far.
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base::TimeDelta GetTimestamp() const;
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// Gets the duration if |frame_count| frames were added to the current
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// timestamp reported by GetTimestamp(). This method ensures that
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// (GetTimestamp() + GetFrameDuration(n)) will equal the timestamp that
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// GetTimestamp() will return if AddFrames(n) is called.
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base::TimeDelta GetFrameDuration(int frame_count) const;
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// Returns the number of frames needed to reach the target timestamp.
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// Note: |target| must be >= |base_timestamp_|.
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int64 GetFramesToTarget(base::TimeDelta target) const;
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private:
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base::TimeDelta ComputeTimestamp(int64 frame_count) const;
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double microseconds_per_frame_;
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base::TimeDelta base_timestamp_;
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// Number of frames accumulated by AddFrames() calls.
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int64 frame_count_;
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DISALLOW_IMPLICIT_CONSTRUCTORS(AudioTimestampHelper);
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};
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} // namespace media
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#endif
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