Move AudioRenderer out of Filter heirarchy.

media/base/audio_renderer.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_H_
 #define MEDIA_BASE_AUDIO_RENDERER_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/time.h"
 #include "media/base/filters.h"
 #include "media/base/media_export.h"
 #include "media/base/pipeline_status.h"
 
 namespace media {
 
 class AudioDecoder;
 
-class MEDIA_EXPORT AudioRenderer : public Filter {
+class MEDIA_EXPORT AudioRenderer
+    : public base::RefCountedThreadSafe<AudioRenderer> {
  public:
-  // Used to update the pipeline's clock time. The first parameter is the
-  // current time, and the second parameter is the time that the clock must not
-  // exceed.
+  // First parameter is the current time that has been rendered.
+  // Second parameter is the maximum time value that the clock cannot exceed.
   typedef base::Callback<void(base::TimeDelta, base::TimeDelta)> TimeCB;
 
   // Initialize a AudioRenderer with the given AudioDecoder, executing the
-  // |init_cb| upon completion. |underflow_cb| is called when the
-  // renderer runs out of data to pass to the audio card during playback.
-  // If the |underflow_cb| is called ResumeAfterUnderflow() must be called
+  // |init_cb| upon completion.
+  //
+  // |underflow_cb| is executed when the renderer runs out of data to pass to
+  // the audio card during playback. ResumeAfterUnderflow() must be called
   // to resume playback. Pause(), Seek(), or Stop() cancels the underflow
   // condition.
+  //
+  // |time_cb| is executed whenever time has advanced by way of audio rendering.
+  //
+  // |ended_cb| is executed when audio rendering has reached the end of stream.
+  //
+  // |disabled_cb| is executed when audio rendering has been disabled due to
+  // external factors (i.e., device was removed). |time_cb| will no longer be
+  // executed.
   virtual void Initialize(const scoped_refptr<AudioDecoder>& decoder,
                           const PipelineStatusCB& init_cb,
                           const base::Closure& underflow_cb,
-                          const TimeCB& time_cb) = 0;
+                          const TimeCB& time_cb,
+                          const base::Closure& ended_cb,

[acolwell GONE FROM CHROMIUM, 2012/07/19 00:58:18]

WDYT of moving this to Play() since it only makes sense to call this while
playing? Clear it when Pause()/Stop() is called. underflow_cb could be moved as
well for the same reasons.

[scherkus (not reviewing), 2012/07/19 21:29:02]

I tried it out but the only difference seemed to be adding even more DCHECKs
along with all the other state DCHECKs -- don't think it's particularly helpful
at the moment

+                          const base::Closure& disabled_cb) = 0;
 
-  // Returns true if this filter has received and processed an end-of-stream
-  // buffer.
+  // Start audio decoding and rendering at the current playback rate, executing
+  // |callback| when playback is underway.
+  virtual void Play(const base::Closure& callback) = 0;
+
+  // Temporarily suspend decoding and rendering audio, executing |callback| when
+  // playback has been suspended.
+  virtual void Pause(const base::Closure& callback) = 0;
+
+  // Discard any audio data, executing |callback| when completed.
+  virtual void Flush(const base::Closure& callback) = 0;
+
+  // Start prerolling audio data for samples starting at |time|, executing
+  // |callback| when completed.
+  //
+  // Only valid to call after a successful Initialize() or Flush().
+  //
+  // TODO(scherkus): rename this to Preroll().
+  virtual void Seek(base::TimeDelta time, const PipelineStatusCB& callback) = 0;
+
+  // Stop all operations in preparation for being deleted, executing |callback|
+  // when complete.
+  virtual void Stop(const base::Closure& callback) = 0;
+
+  // Updates the current playback rate.
+  virtual void SetPlaybackRate(float playback_rate) = 0;
+
+  // Returns true if all audio data has been played back by the audio device.
   virtual bool HasEnded() = 0;
 
   // Sets the output volume.
   virtual void SetVolume(float volume) = 0;
 
   // Resumes playback after underflow occurs.
+  //
   // |buffer_more_audio| is set to true if you want to increase the size of the
   // decoded audio buffer.
   virtual void ResumeAfterUnderflow(bool buffer_more_audio) = 0;
 
  protected:
+  friend class base::RefCountedThreadSafe<AudioRenderer>;
   virtual ~AudioRenderer() {}
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_AUDIO_RENDERER_H_