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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_AUDIO_DISCARD_HELPER_H_
#define MEDIA_BASE_AUDIO_DISCARD_HELPER_H_
#include <stddef.h>
#include "base/memory/ref_counted.h"
#include "base/time/time.h"
#include "media/base/audio_timestamp_helper.h"
#include "media/base/decoder_buffer.h"
#include "media/base/media_export.h"
#include "media/base/timestamp_constants.h"
namespace media {
class AudioBuffer;
// Helper class for managing timestamps and discard events around decoding.
class MEDIA_EXPORT AudioDiscardHelper {
public:
AudioDiscardHelper() = delete;
// |sample_rate| is the sample rate of decoded data which will be handed into
// the ProcessBuffers() call.
//
// |decoder_delay| is the number of frames a decoder will output before data
// corresponding to the first encoded buffer is output. Callers only need to
// specify this if the decoder inserts frames which have no corresponding
// encoded buffer.
//
// |delayed_discard| indicates that the codec requires two encoded buffers
// before the first decoded output buffer. Used only for vorbis currently.
//
// For example, most MP3 decoders will output 529 junk frames before the data
// corresponding to the first encoded buffer is output. These frames are not
// represented in the encoded data stream and instead are an artifact of how
// most MP3 decoders work. See http://lame.sourceforge.net/tech-FAQ.txt
AudioDiscardHelper(int sample_rate,
size_t decoder_delay,
bool delayed_discard);
AudioDiscardHelper(const AudioDiscardHelper&) = delete;
AudioDiscardHelper& operator=(const AudioDiscardHelper&) = delete;
~AudioDiscardHelper();
// Converts a TimeDelta to a frame count based on the constructed sample rate.
// |duration| must be positive.
size_t TimeDeltaToFrames(base::TimeDelta duration) const;
// Resets internal state and indicates that |initial_discard| of upcoming
// frames should be discarded.
void Reset(size_t initial_discard);
// Applies discard padding from |time_info| along with any initial discards.
// |decoded_buffer| may be NULL, if not the timestamp and duration will be set
// after discards are applied. Returns true if |decoded_buffer| exists after
// processing discard events. Returns false if |decoded_buffer| was NULL, is
// completely discarded, or a processing error occurs.
//
// If AudioDiscardHelper is not initialized() the timestamp of the first
// |time_info| will be used as the basis for all future timestamps set on
// |decoded_buffer|s. If the first |time_info| has a negative timestamp it
// will be clamped to zero.
bool ProcessBuffers(const DecoderBuffer::TimeInfo& time_info,
AudioBuffer* decoded_buffer);
// Whether any buffers have been processed.
bool initialized() const {
return timestamp_helper_.base_timestamp() != kNoTimestamp;
}
size_t decoder_delay() const { return decoder_delay_; }
private:
// The sample rate of the decoded audio samples. Used by TimeDeltaToFrames()
// and the timestamp helper.
const int sample_rate_;
// Some codecs output extra samples during the first decode. In order to trim
// DiscardPadding correctly the helper must know the offset into the decoded
// buffers at which real samples start.
const size_t decoder_delay_;
// Used to regenerate sample accurate timestamps for decoded buffers. The
// timestamp of the first encoded buffer seen by ProcessBuffers() is used as
// the base timestamp.
AudioTimestampHelper timestamp_helper_;
// The number of frames to discard from the front of the next buffer. Can be
// set by Reset() and added to by a front DiscardPadding larger than its
// associated buffer.
size_t discard_frames_;
// The last encoded buffer timestamp seen by ProcessBuffers() or kNoTimestamp
// if no buffers have been seen thus far. Used to issue warnings for buffer
// sequences with non-monotonic timestamps.
base::TimeDelta last_input_timestamp_;
// Certain codecs require two encoded buffers before they'll output the first
// decoded buffer. In this case DiscardPadding must be carried over from the
// previous encoded buffer. Set during construction.
const bool delayed_discard_;
DecoderBuffer::DiscardPadding delayed_discard_padding_;
// When |decoder_delay_| > 0, the number of frames which should be discarded
// from the next buffer. The index at which to start discarding is calculated
// by subtracting |delayed_end_discard_| from |decoder_delay_|.
size_t delayed_end_discard_;
};
} // namespace media
#endif // MEDIA_BASE_AUDIO_DISCARD_HELPER_H_
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