Second layer of mixing for audio elements.

media/base/audio_renderer_mixer.h

Index: media/base/audio_renderer_mixer.h
diff --git a/media/base/audio_renderer_mixer.h b/media/base/audio_renderer_mixer.h
index 9bc383934d4e43a9a764ff5eb052fbeb7e286452..e8a0f8d92430c1c5f1bb494e47899da9e5a6b00d 100644
--- a/media/base/audio_renderer_mixer.h
+++ b/media/base/audio_renderer_mixer.h
@@ -8,10 +8,12 @@
 #include <map>
 #include <string>
 
+#include "base/memory/scoped_ptr.h"
 #include "base/synchronization/lock.h"
 #include "base/time/time.h"
 #include "media/base/audio_converter.h"
 #include "media/base/audio_renderer_sink.h"
+#include "media/base/loopback_audio_converter.h"
 
 namespace media {
 
@@ -21,14 +23,15 @@ namespace media {
 class MEDIA_EXPORT AudioRendererMixer
     : NON_EXPORTED_BASE(public AudioRendererSink::RenderCallback) {
  public:
-  AudioRendererMixer(const AudioParameters& input_params,
-                     const AudioParameters& output_params,
+  AudioRendererMixer(const AudioParameters& output_params,
                      const scoped_refptr<AudioRendererSink>& sink);
   ~AudioRendererMixer() override;
 
   // Add or remove a mixer input from mixing; called by AudioRendererMixerInput.
-  void AddMixerInput(AudioConverter::InputCallback* input);
-  void RemoveMixerInput(AudioConverter::InputCallback* input);
+  void AddMixerInput(const AudioParameters& input_params,
+                     AudioConverter::InputCallback* input);
+  void RemoveMixerInput(const AudioParameters& input_params,
+                        AudioConverter::InputCallback* input);
 
   // Since errors may occur even when no inputs are playing, an error callback
   // must be registered separately from adding a mixer input.  The same callback
@@ -47,13 +50,23 @@ class MEDIA_EXPORT AudioRendererMixer
   OutputDevice* GetOutputDevice();
 
  private:
+  // Maps input sample rate to the dedicated converter.
+  typedef std::map<int, scoped_ptr<LoopbackAudioConverter>> AudioConvertersMap;
+
   // AudioRendererSink::RenderCallback implementation.
   int Render(AudioBus* audio_bus, int audio_delay_milliseconds) override;
   void OnRenderError() override;
 
+  bool is_master_sample_rate(int sample_rate) {
+    return sample_rate == output_params_.sample_rate();
+  }
+
   // Output sink for this mixer.
   scoped_refptr<AudioRendererSink> audio_sink_;
 
+  // Output parameters for this mixer.
+  AudioParameters output_params_;
+
   // ---------------[ All variables below protected by |lock_| ]---------------
   base::Lock lock_;
 
@@ -61,8 +74,14 @@ class MEDIA_EXPORT AudioRendererMixer
   typedef std::list<base::Closure> ErrorCallbackList;
   ErrorCallbackList error_callbacks_;
 
-  // Handles mixing and resampling between input and output parameters.
-  AudioConverter audio_converter_;
+  // Each of these converters mixes inputs with a given sample rate and
+  // resamples them to the output sample rate. Inputs not reqiuring resampling
+  // go directly to |master_converter_|.
+  AudioConvertersMap converters_;
+
+  // Master converter which mixes all the outputs from |converters_| as well as
+  // mixer inputs that are in the output sample rate.
+  AudioConverter master_converter_;
 
   // Handles physical stream pause when no inputs are playing.  For latency
   // reasons we don't want to immediately pause the physical stream.