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 <map>
#include <string>

#include "base/synchronization/lock.h"
#include "base/time/time.h"
#include "media/base/audio_converter.h"
#include "media/base/audio_renderer_sink.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& input_params,
                     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);

  // 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;
  }

  // TODO(guidou): remove this method. The output device of a mixer should
  // never be switched, as it may result in a discrepancy between the output
  // parameters of the new device and the output parameters with which the
  // mixer was initialized. See crbug.com/506507
  OutputDevice* GetOutputDevice();

 private:
  // AudioRendererSink::RenderCallback implementation.
  int Render(AudioBus* audio_bus, int audio_delay_milliseconds) override;
  void OnRenderError() override;

  // Output sink for this mixer.
  scoped_refptr<AudioRendererSink> audio_sink_;

  // ---------------[ All variables below protected by |lock_| ]---------------
  base::Lock lock_;

  // List of error callbacks used by this mixer.
  typedef std::list<base::Closure> ErrorCallbackList;
  ErrorCallbackList error_callbacks_;

  // Handles mixing and resampling between input and output parameters.
  AudioConverter audio_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_;

  DISALLOW_COPY_AND_ASSIGN(AudioRendererMixer);
};

}  // namespace media

#endif  // MEDIA_BASE_AUDIO_RENDERER_MIXER_H_