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      1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #ifndef MEDIA_AUDIO_AUDIO_OUTPUT_RESAMPLER_H_
      6 #define MEDIA_AUDIO_AUDIO_OUTPUT_RESAMPLER_H_
      7 
      8 #include <map>
      9 
     10 #include "base/basictypes.h"
     11 #include "base/memory/ref_counted.h"
     12 #include "base/time/time.h"
     13 #include "media/audio/audio_io.h"
     14 #include "media/audio/audio_manager.h"
     15 #include "media/audio/audio_output_dispatcher.h"
     16 #include "media/audio/audio_parameters.h"
     17 
     18 namespace media {
     19 
     20 class OnMoreDataConverter;
     21 
     22 // AudioOutputResampler is a browser-side resampling and buffering solution
     23 // which ensures audio data is always output at given parameters.  See the
     24 // AudioConverter class for details on the conversion process.
     25 //
     26 // AOR works by intercepting the AudioSourceCallback provided to StartStream()
     27 // and redirecting it through an AudioConverter instance.  AudioBuffersState is
     28 // adjusted for buffer delay caused by the conversion process.
     29 //
     30 // AOR will automatically fall back from AUDIO_PCM_LOW_LATENCY to
     31 // AUDIO_PCM_LINEAR if the output device fails to open at the requested output
     32 // parameters.
     33 //
     34 // TODO(dalecurtis): Ideally the low latency path will be as reliable as the
     35 // high latency path once we have channel mixing and support querying for the
     36 // hardware's configured bit depth.  Monitor the UMA stats for fallback and
     37 // remove fallback support once it's stable.  http://crbug.com/148418
     38 class MEDIA_EXPORT AudioOutputResampler : public AudioOutputDispatcher {
     39  public:
     40   AudioOutputResampler(AudioManager* audio_manager,
     41                        const AudioParameters& input_params,
     42                        const AudioParameters& output_params,
     43                        const std::string& output_device_id,
     44                        const base::TimeDelta& close_delay);
     45 
     46   // AudioOutputDispatcher interface.
     47   virtual bool OpenStream() OVERRIDE;
     48   virtual bool StartStream(AudioOutputStream::AudioSourceCallback* callback,
     49                            AudioOutputProxy* stream_proxy) OVERRIDE;
     50   virtual void StopStream(AudioOutputProxy* stream_proxy) OVERRIDE;
     51   virtual void StreamVolumeSet(AudioOutputProxy* stream_proxy,
     52                                double volume) OVERRIDE;
     53   virtual void CloseStream(AudioOutputProxy* stream_proxy) OVERRIDE;
     54   virtual void Shutdown() OVERRIDE;
     55 
     56  private:
     57   friend class base::RefCountedThreadSafe<AudioOutputResampler>;
     58   virtual ~AudioOutputResampler();
     59 
     60   // Converts low latency based output parameters into high latency
     61   // appropriate output parameters in error situations.
     62   void SetupFallbackParams();
     63 
     64   // Used to initialize and reinitialize |dispatcher_|.
     65   void Initialize();
     66 
     67   // Dispatcher to proxy all AudioOutputDispatcher calls too.
     68   scoped_refptr<AudioOutputDispatcher> dispatcher_;
     69 
     70   // Map of outstanding OnMoreDataConverter objects.  A new object is created
     71   // on every StartStream() call and destroyed on CloseStream().
     72   typedef std::map<AudioOutputProxy*, OnMoreDataConverter*> CallbackMap;
     73   CallbackMap callbacks_;
     74 
     75   // Used by AudioOutputDispatcherImpl; kept so we can reinitialize on the fly.
     76   base::TimeDelta close_delay_;
     77 
     78   // AudioParameters used to setup the output stream.
     79   AudioParameters output_params_;
     80 
     81   // Whether any streams have been opened through |dispatcher_|, if so we can't
     82   // fallback on future OpenStream() failures.
     83   bool streams_opened_;
     84 
     85   DISALLOW_COPY_AND_ASSIGN(AudioOutputResampler);
     86 };
     87 
     88 }  // namespace media
     89 
     90 #endif  // MEDIA_AUDIO_AUDIO_OUTPUT_RESAMPLER_H_
     91