Collapse AudioRendererMixer and OnMoreDataResampler into AudioTransform.

media/audio/audio_output_resampler.h

 // 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/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;
+class OnMoreDataTransform;

[Chris Rogers, 2012/11/14 23:50:49]

OnMoreDataTransform sounds a bit awkward, how about OnMoreDataConverter?

In general, I recommend avoiding the word "transform" since this often implies
audio effects processing.  Instead, I'd recommend "converter".

[DaleCurtis, 2012/11/16 23:51:05]

Done.

 
 // 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.
+  // Used to initialize and reinitialize |dispatcher_|.
   void Initialize();
 
   // Dispatcher to proxy all AudioOutputDispatcher calls too.
   scoped_refptr<AudioOutputDispatcher> dispatcher_;
 
-  // Map of outstanding OnMoreDataResampler objects.  A new object is created
+  // Map of outstanding OnMoreDataTransform objects.  A new object is created
   // on every StartStream() call and destroyed on CloseStream().
-  typedef std::map<AudioOutputProxy*, OnMoreDataResampler*> CallbackMap;
+  typedef std::map<AudioOutputProxy*, OnMoreDataTransform*> CallbackMap;
   CallbackMap callbacks_;
 
-  // 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_;
 
   // Whether any streams have been opened through |dispatcher_|, if so we can't
   // fallback on future OpenStream() failures.
   bool streams_opened_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioOutputResampler);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_AUDIO_OUTPUT_RESAMPLER_H_