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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_AUDIO_AUDIO_OUTPUT_RESAMPLER_H_
#define MEDIA_AUDIO_AUDIO_OUTPUT_RESAMPLER_H_
#include <map>
#include "base/basictypes.h"
#include "base/memory/ref_counted.h"
#include "base/synchronization/lock.h"
#include "base/time.h"
#include "media/audio/audio_io.h"
#include "media/audio/audio_manager.h"
#include "media/audio/audio_output_dispatcher.h"
#include "media/audio/audio_parameters.h"
namespace media {
class OnMoreDataResampler;
// AudioOutputResampler is a browser-side resampling and rebuffering solution
// which ensures audio data is always output at given parameters. The rough
// flow is: Client -> [FIFO] -> [Resampler] -> Output Device.
//
// The FIFO and resampler are only used when necessary. To be clear:
// - The resampler is only used if the input and output sample rates differ.
// - The FIFO is only used if the input and output frame sizes differ or if
// the resampler is used.
//
// AOR works by intercepting the AudioSourceCallback provided to StartStream()
// and redirecting to the appropriate resampling or FIFO callback which passes
// through to the original callback only when necessary.
//
// AOR will automatically fall back from AUDIO_PCM_LOW_LATENCY to
// AUDIO_PCM_LINEAR if the output device fails to open at the requested output
// parameters.
// TODO(dalecurtis): Ideally the low latency path will be as reliable as the
// high latency path once we have channel mixing and support querying for the
// hardware's configured bit depth. Monitor the UMA stats for fallback and
// remove fallback support once it's stable. http://crbug.com/148418
//
// Currently channel downmixing and upmixing is not supported.
// TODO(dalecurtis): Add channel remixing. http://crbug.com/138762
class MEDIA_EXPORT AudioOutputResampler
: public AudioOutputDispatcher {
public:
AudioOutputResampler(AudioManager* audio_manager,
const AudioParameters& input_params,
const AudioParameters& output_params,
const base::TimeDelta& close_delay);
// AudioOutputDispatcher interface.
virtual bool OpenStream() OVERRIDE;
virtual bool StartStream(AudioOutputStream::AudioSourceCallback* callback,
AudioOutputProxy* stream_proxy) OVERRIDE;
virtual void StopStream(AudioOutputProxy* stream_proxy) OVERRIDE;
virtual void StreamVolumeSet(AudioOutputProxy* stream_proxy,
double volume) OVERRIDE;
virtual void CloseStream(AudioOutputProxy* stream_proxy) OVERRIDE;
virtual void Shutdown() OVERRIDE;
private:
friend class base::RefCountedThreadSafe<AudioOutputResampler>;
virtual ~AudioOutputResampler();
// Used to initialize the FIFO and resamplers.
void Initialize();
// Used by StopStream()/CloseStream() to clear internal state. When
// |delete_callback| is set, the callbacks[stream_proxy] is destroyed.
void Reset(AudioOutputProxy* stream_proxy, bool delete_callback);
// Dispatcher to proxy all AudioOutputDispatcher calls too.
scoped_refptr<AudioOutputDispatcher> dispatcher_;
// Vector of each outstanding OnMoreDataResampler object. A new instance is
// created on every StartStream() call. Access must be locked.
typedef std::map<AudioOutputProxy*, OnMoreDataResampler*> CallbackMap;
CallbackMap callbacks_;
base::Lock callbacks_lock_;
// Ratio of input bytes to output bytes used to correct playback delay with
// regard to buffering and resampling.
double io_ratio_;
// Used by AudioOutputDispatcherImpl; kept so we can reinitialize on the fly.
base::TimeDelta close_delay_;
// AudioParameters used to setup the output stream.
AudioParameters output_params_;
DISALLOW_COPY_AND_ASSIGN(AudioOutputResampler);
};
} // namespace media
#endif // MEDIA_AUDIO_AUDIO_OUTPUT_RESAMPLER_H_
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