media/base/audio_renderer_sink.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_SINK_H_
#define MEDIA_BASE_AUDIO_RENDERER_SINK_H_

#include <stdint.h>

#include <string>

#include "base/callback.h"
#include "base/memory/ref_counted.h"
#include "media/base/audio_bus.h"
#include "media/base/audio_parameters.h"
#include "media/base/output_device_info.h"

namespace media {

// AudioRendererSink is an interface representing the end-point for
// rendered audio.  An implementation is expected to
// periodically call Render() on a callback object.

class AudioRendererSink
    : public base::RefCountedThreadSafe<media::AudioRendererSink> {
 public:
  class RenderCallback {
   public:
    // Attempts to completely fill all channels of |dest|, returns actual
    // number of frames filled. |prior_frames_skipped| contains the number of
    // frames
    // the consumer has skipped, if any.
    // The |delay| argument represents audio device output latency,
    // |delay_timestamp| represents the time when |delay| was obtained.
    virtual int Render(base::TimeDelta delay,
                       base::TimeTicks delay_timestamp,
                       int prior_frames_skipped,
                       AudioBus* dest) = 0;
    // Signals an error has occurred.
    virtual void OnRenderError() = 0;

   protected:
    virtual ~RenderCallback() {}
  };

  // Sets important information about the audio stream format.
  // It must be called before any of the other methods.
  virtual void Initialize(const AudioParameters& params,
                          RenderCallback* callback) = 0;

  // Starts audio playback.
  virtual void Start() = 0;

  // Stops audio playback and performs cleanup. It must be called before
  // destruction.
  virtual void Stop() = 0;

  // Pauses playback.
  virtual void Pause() = 0;

  // Resumes playback after calling Pause().
  virtual void Play() = 0;

  // Sets the playback volume, with range [0.0, 1.0] inclusive.
  // Returns |true| on success.
  virtual bool SetVolume(double volume) = 0;

  // Returns current output device information. If the information is not
  // available yet, this method may block until it becomes available. If the
  // sink is not associated with any output device, |device_status| of
  // OutputDeviceInfo should be set to OUTPUT_DEVICE_STATUS_ERROR_INTERNAL. Must
  // never be called on the IO thread.
  //
  // Note: Prefer to use GetOutputDeviceInfoAsync instead if possible.
  virtual OutputDeviceInfo GetOutputDeviceInfo() = 0;

  // Same as the above, but does not block and will execute |info_cb| when the
  // OutputDeviceInfo is available. Callback will be executed on the calling
  // thread. Prefer this function to the synchronous version, it does not have a
  // timeout so will result in less spurious timeout errors.
  //
  // |info_cb| will always be posted (I.e., executed after this function
  // returns), even if OutputDeviceInfo is already available.
  //
  // Upon destruction if OutputDeviceInfo is still not available, |info_cb| will
  // be posted with OUTPUT_DEVICE_STATUS_ERROR_INTERNAL. Note: Because |info_cb|
  // is posted it will execute after destruction, so clients must handle
  // cancellation of the callback if needed.
  using OutputDeviceInfoCB = base::OnceCallback<void(OutputDeviceInfo)>;
  virtual void GetOutputDeviceInfoAsync(OutputDeviceInfoCB info_cb) = 0;

  // Returns |true| if a source with hardware parameters is preferable.
  virtual bool IsOptimizedForHardwareParameters() = 0;

  // If DCHECKs are enabled, this function returns true if called on rendering
  // thread, otherwise false. With DCHECKs disabled, it returns true. Thus, it
  // is intended to be used for DCHECKing.
  virtual bool CurrentThreadIsRenderingThread() = 0;

 protected:
  friend class base::RefCountedThreadSafe<AudioRendererSink>;
  virtual ~AudioRendererSink() {}
};

// Same as AudioRendererSink except that Initialize() and Start() can be called
// again after Stop().
// TODO(sandersd): Fold back into AudioRendererSink once all subclasses support
// this.

class RestartableAudioRendererSink : public AudioRendererSink {
 protected:
  ~RestartableAudioRendererSink() override {}
};

class SwitchableAudioRendererSink : public RestartableAudioRendererSink {
 public:
  // Attempts to switch the audio output device associated with a sink.
  // Once the attempt is finished, |callback| is invoked with the
  // result of the operation passed as a parameter. The result is a value from
  // the media::OutputDeviceStatus enum.
  // There is no guarantee about the thread where |callback| will be invoked.
  virtual void SwitchOutputDevice(const std::string& device_id,
                                  OutputDeviceStatusCB callback) = 0;

 protected:
  ~SwitchableAudioRendererSink() override {}
};

}  // namespace media

#endif  // MEDIA_BASE_AUDIO_RENDERER_SINK_H_