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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.
#include "base/memory/ref_counted.h"
#include "base/memory/scoped_ptr.h"
#include "base/time/time.h"
#include "media/audio/audio_parameters.h"
#include "media/base/buffers.h"
#include "media/base/media_export.h"
namespace media {
class AudioBuffer;
class AudioBus;
class AudioStreamSanitizer;
// Helper class that handles filling gaps and resolving overlaps.
class MEDIA_EXPORT AudioSplicer {
explicit AudioSplicer(int samples_per_second);
enum {
// The number of ms to crossfade before trimming when buffers overlap.
kCrossfadeDurationInMilliseconds = 5,
// Largest gap or overlap allowed between buffers. Anything larger than
// this will trigger an error. This is an arbitrary value, but the initial
// selection of 50ms roughly represents the duration of 2 compressed AAC or
// MP3 frames.
kMaxTimeDeltaInMilliseconds = 50,
// Resets the splicer state by clearing the output buffers queue and resetting
// the timestamp helper.
void Reset();
// Adds a new buffer full of samples or end of stream buffer to the splicer.
// Returns true if the buffer was accepted. False is returned if an error
// occurred.
bool AddInput(const scoped_refptr<AudioBuffer>& input);
// Returns true if the splicer has a buffer to return.
bool HasNextBuffer() const;
// Removes the next buffer from the output buffer queue and returns it; this
// should only be called if HasNextBuffer() returns true.
scoped_refptr<AudioBuffer> GetNextBuffer();
// Indicates an upcoming splice point. All buffers overlapping or after the
// |splice_timestamp| will be considered as "before the splice." Clients must
// then call SetSpliceTimestamp(kNoTimestamp()) to signal that future buffers
// should be considered as "after the splice."
// Once |kCrossfadeDurationInMilliseconds| of buffers "after the splice" or
// end of stream has been received, the "after" buffers will be crossfaded
// with all "before" buffers which overlap them. "before" buffers outside
// of the overlap range will be discarded.
void SetSpliceTimestamp(base::TimeDelta splice_timestamp);
friend class AudioSplicerTest;
// Extracts frames to be crossfaded from |pre_splice_sanitizer_|. Transfers
// all frames before |splice_timestamp_| into |output_sanitizer_| and drops
// frames outside of the crossfade duration.
// The size of the returned AudioBus is the crossfade duration in frames.
// Crossfade duration is calculated based on the number of frames available
// after |splice_timestamp_| in each sanitizer and capped by
// |max_crossfade_duration_|.
// |pre_splice_sanitizer_| will be empty after this operation.
scoped_ptr<AudioBus> ExtractCrossfadeFromPreSplice(
scoped_refptr<AudioBuffer>* crossfade_buffer);
// Crossfades |pre_splice_bus->frames()| frames from
// |post_splice_sanitizer_|
// with those from |pre_splice_bus|. Adds the crossfaded buffer to
// |output_sanitizer_| along with all buffers in |post_splice_sanitizer_|.
// |post_splice_sanitizer_| will be empty after this operation.
void CrossfadePostSplice(scoped_ptr<AudioBus> pre_splice_bus,
scoped_refptr<AudioBuffer> crossfade_buffer);
// Reset the splice and splice end timestamps.
void reset_splice_timestamps() {
splice_timestamp_ = max_splice_end_timestamp_ = kNoTimestamp();
const base::TimeDelta max_crossfade_duration_;
base::TimeDelta splice_timestamp_;
base::TimeDelta max_splice_end_timestamp_;
// The various sanitizers for each stage of the crossfade process. Buffers in
// |output_sanitizer_| are immediately available for consumption by external
// callers.
// Overlapped buffers go into the |pre_splice_sanitizer_| while overlapping
// buffers go into the |post_splice_sanitizer_|. Once enough buffers for
// crossfading are received the pre and post sanitizers are drained into
// |output_sanitizer_| by the two ExtractCrossfadeFromXXX methods above.
// |pre_splice_sanitizer_| is not constructed until the first splice frame is
// encountered. At which point it is constructed based on the timestamp state
// of |output_sanitizer_|. It is destructed once the splice is finished.
scoped_ptr<AudioStreamSanitizer> output_sanitizer_;
scoped_ptr<AudioStreamSanitizer> pre_splice_sanitizer_;
scoped_ptr<AudioStreamSanitizer> post_splice_sanitizer_;
// Whether all buffers which should go into |pre_splice_sanitizer_| have been
// received. If true, buffers should now be put in |post_splice_sanitizer_|.
bool have_all_pre_splice_buffers_;
} // namespace media