Switch to pcm_low_latency and enable resampling.

media/base/audio_renderer_mixer.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_BASE_AUDIO_RENDERER_MIXER_H_
 #define MEDIA_BASE_AUDIO_RENDERER_MIXER_H_
 
 #include <set>
 #include <vector>
 
 #include "base/memory/ref_counted.h"
 #include "base/synchronization/lock.h"
 #include "media/base/audio_renderer_mixer_input.h"
 #include "media/base/audio_renderer_sink.h"
+#include "media/base/multi_channel_resampler.h"
 
 namespace media {
 
 // Mixes a set of AudioRendererMixerInputs into a single output stream which is
 // funneled into a single shared AudioRendererSink; saving a bundle on renderer
-// side resources.
-// TODO(dalecurtis): Update documentation once resampling is available.
+// side resources.  Resampling is done post-mixing as it is the most expensive
+// process.  If the input sample rate matches the audio hardware sample rate, no
+// resampling is done.
 class MEDIA_EXPORT AudioRendererMixer
     : public base::RefCountedThreadSafe<AudioRendererMixer>,
-      NON_EXPORTED_BASE(public AudioRendererSink::RenderCallback) {
+      NON_EXPORTED_BASE(public AudioRendererSink::RenderCallback),
+      NON_EXPORTED_BASE(
+          public MultiChannelResampler::MultiChannelAudioSourceProvider) {
  public:
   AudioRendererMixer(const AudioParameters& params,
                      const scoped_refptr<AudioRendererSink>& sink);
 
   // Add or remove a mixer input from mixing; called by AudioRendererMixerInput.
   void AddMixerInput(const scoped_refptr<AudioRendererMixerInput>& input);
   void RemoveMixerInput(const scoped_refptr<AudioRendererMixerInput>& input);
 
  protected:
   friend class base::RefCountedThreadSafe<AudioRendererMixer>;
   virtual ~AudioRendererMixer();
 
  private:
   // AudioRendererSink::RenderCallback implementation.
   virtual int Render(const std::vector<float*>& audio_data,
                      int number_of_frames,
                      int audio_delay_milliseconds) OVERRIDE;
   virtual void OnRenderError() OVERRIDE;
 
-  // AudioParameters this mixer was constructed with.
-  AudioParameters audio_parameters_;
+  // MultiChannelResampler::MultiChannelAudioSourceProvider implementation and
+  // main worker method for AudioRendererMixer.  Handles mixing and volume
+  // adjustment.  Renders |number_of_frames| into |audio_data|.  When resampling
+  // is necessary, ProvideInput() will be called by MultiChannelResampler when
+  // more data is necessary.
+  virtual void ProvideInput(const std::vector<float*>& audio_data,
+                            int number_of_frames) OVERRIDE;
+
+  // AudioParameters this mixer will output with.
+  AudioParameters output_parameters_;
 
   // Output sink for this mixer.
   scoped_refptr<AudioRendererSink> audio_sink_;
 
   // Set of mixer inputs to be mixed by this mixer.  Access is thread-safe
   // through |mixer_inputs_lock_|.
   typedef std::set< scoped_refptr<AudioRendererMixerInput> >
       AudioRendererMixerInputSet;
   AudioRendererMixerInputSet mixer_inputs_;
   base::Lock mixer_inputs_lock_;
 
+  // Vector for rendering audio data from each mixer input.
+  std::vector<float*> mixer_input_audio_data_;
+
+  // Handles resampling post-mixing.
+  scoped_ptr<MultiChannelResampler> resampler_;
+
+  // The audio delay in milliseconds received by the last Render() call.
+  int current_audio_delay_milliseconds_;
+
   DISALLOW_COPY_AND_ASSIGN(AudioRendererMixer);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_AUDIO_RENDERER_MIXER_H_