Allow better AudioRendererMixer reuse by ignoring irrelevant params.

content/renderer/media/audio_renderer_mixer_manager.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 CONTENT_RENDERER_MEDIA_AUDIO_RENDERER_MIXER_MANAGER_H_
 #define CONTENT_RENDERER_MEDIA_AUDIO_RENDERER_MIXER_MANAGER_H_
 
 #include <map>
 #include <utility>
 
@@ skipping 50 matching lines @@
   // Remove a mixer instance given a mixer if the only other reference is held
   // by AudioRendererMixerManager.  Every AudioRendererMixer owner must call
   // this method when it's done with a mixer.
   void RemoveMixer(int source_render_view_id,
                    const media::AudioParameters& params);
 
  private:
   friend class AudioRendererMixerManagerTest;
 
   // Define a key so that only those AudioRendererMixerInputs from the same
-  // RenderView and with the same AudioParameters can be mixed together.
+  // RenderView and with the same AudioParameters can be mixed together.  The
+  // first value is the RenderViewId.
   typedef std::pair<int, media::AudioParameters> MixerKey;
 
+  // Custom compare operator for the AudioRendererMixerMap.  Allows reuse of
+  // mixers where only irrelevant keys mismatch; e.g., effects, bits per sample.
+  struct MixerKeyCompare {
+    bool operator()(const MixerKey& a, const MixerKey& b) const {
+      if (a.first != b.first)
+        return a.first < b.first;
+      if (a.second.sample_rate() != b.second.sample_rate())
+        return a.second.sample_rate() < b.second.sample_rate();
+      if (a.second.channels() != b.second.channels())
+        return a.second.channels() < b.second.channels();
+
+      // Ignore effects(), bits_per_sample(), format(), and frames_per_buffer(),
+      // these parameters do not affect mixer reuse.  All AudioRendererMixer
+      // units disable FIFO, so frames_per_buffer() can be safely ignored.
+      return a.second.channel_layout() < b.second.channel_layout();
+    }
+  };
+
   // Map of MixerKey to <AudioRendererMixer, Count>.  Count allows
   // AudioRendererMixerManager to keep track explicitly (v.s. RefCounted which
   // is implicit) of the number of outstanding AudioRendererMixers.
   struct AudioRendererMixerReference {
     media::AudioRendererMixer* mixer;
     int ref_count;
   };
-  typedef std::map<MixerKey, AudioRendererMixerReference> AudioRendererMixerMap;
+  typedef std::map<MixerKey, AudioRendererMixerReference, MixerKeyCompare>
+      AudioRendererMixerMap;
 
   // Overrides the AudioRendererSink implementation for unit testing.
   void SetAudioRendererSinkForTesting(media::AudioRendererSink* sink);
 
   // Active mixers.
   AudioRendererMixerMap mixers_;
   base::Lock mixers_lock_;
 
   // Audio hardware configuration.  Used to construct output AudioParameters for
   // each AudioRendererMixer instance.
   media::AudioHardwareConfig* const hardware_config_;
 
   media::AudioRendererSink* sink_for_testing_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioRendererMixerManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_AUDIO_RENDERER_MIXER_MANAGER_H_