media/audio/audio_output_resampler.h

   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_