Mixing audio with different latency requirements

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 <stdint.h>
 
 #include <map>
 #include <memory>
 #include <string>
 
 #include "base/macros.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 {
 
 // Mixes a set of AudioConverter::InputCallbacks into a single output stream
 // which is funneled into a single shared AudioRendererSink; saving a bundle
 // on renderer side resources.
 class MEDIA_EXPORT AudioRendererMixer
     : NON_EXPORTED_BASE(public AudioRendererSink::RenderCallback) {
  public:
   AudioRendererMixer(const AudioParameters& output_params,
-                     scoped_refptr<AudioRendererSink> sink);
+                     scoped_refptr<AudioRendererSink> sink,
+                     const std::string& uma_histogram);
   ~AudioRendererMixer() override;
 
   // Add or remove a mixer input from mixing; called by AudioRendererMixerInput.
   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
   // must be given to both the functions.
   void AddErrorCallback(const base::Closure& error_cb);
   void RemoveErrorCallback(const base::Closure& error_cb);
 
   void set_pause_delay_for_testing(base::TimeDelta delay) {
     pause_delay_ = delay;
   }
 
   OutputDeviceInfo GetOutputDeviceInfo();
 
   // Returns true if called on rendering thread, otherwise false.
   bool CurrentThreadIsRenderingThread();
 
+  AudioParameters GetOutputParamsForTesting() { return output_params_; };
+
  private:
+  class UMAMaxValueTracker;
+
   // Maps input sample rate to the dedicated converter.
   using AudioConvertersMap =
       std::map<int, std::unique_ptr<LoopbackAudioConverter>>;
 
   // AudioRendererSink::RenderCallback implementation.
   int Render(AudioBus* audio_bus,
              uint32_t frames_delayed,
              uint32_t frames_skipped) override;
   void OnRenderError() override;
 
@@ skipping 22 matching lines @@
   // 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.
   base::TimeDelta pause_delay_;
   base::TimeTicks last_play_time_;
   bool playing_;
 
+  // Tracks the maximum number of simultaneous mixer inputs and logs it into
+  // UMA histogram upon the destruction.
+  std::unique_ptr<UMAMaxValueTracker> input_count_tracker_;
+
   DISALLOW_COPY_AND_ASSIGN(AudioRendererMixer);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_AUDIO_RENDERER_MIXER_H_