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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 <stdint.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:
- // Returns the time duration of the given number of frames of audio with the
- // given sample rate (in samples per second).
- static base::TimeDelta FramesToTime(int64_t frames, int samples_per_second);
- // Returns the number of frames in the given duration of audio with the given
- // sample rate (in samples per second).
- static int64_t TimeToFrames(base::TimeDelta time, int samples_per_second);
- AudioTimestampHelper() = delete;
- explicit AudioTimestampHelper(int samples_per_second);
- AudioTimestampHelper(const AudioTimestampHelper&) = delete;
- AudioTimestampHelper& operator=(const AudioTimestampHelper&) = delete;
- // 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_t 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 of |frame_count| frames by calculating the difference
- // between the current timestamp and what the timestamp would be if
- // |frame_count| frames were added.
- 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_t GetFramesToTarget(base::TimeDelta target) const;
- private:
- base::TimeDelta ComputeTimestamp(int64_t frame_count) const;
- double microseconds_per_frame_;
- base::TimeDelta base_timestamp_;
- // Number of frames accumulated by AddFrames() calls.
- int64_t frame_count_;
- };
- } // namespace media
- #endif // MEDIA_BASE_AUDIO_TIMESTAMP_HELPER_H_
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