media::WebAudioSourceProviderImpl, add support for getting a copy of passing AudioBuses

media/blink/webaudiosourceprovider_impl.h

Index: media/blink/webaudiosourceprovider_impl.h
diff --git a/media/blink/webaudiosourceprovider_impl.h b/media/blink/webaudiosourceprovider_impl.h
index afdf1e3ce8dc6364b5c0d3d5b80e45084a1bf2d2..ad60782ee857cd9a52ff6133729c17c7df95e5df 100644
--- a/media/blink/webaudiosourceprovider_impl.h
+++ b/media/blink/webaudiosourceprovider_impl.h
@@ -24,19 +24,29 @@ class WebAudioSourceProviderClient;
 
 namespace media {
 
-// WebAudioSourceProviderImpl provides a bridge between classes:
-//     blink::WebAudioSourceProvider <---> AudioRendererSink
+// WebAudioSourceProviderImpl is either one of two things (but not both):

[DaleCurtis, 2016/03/11 18:45:59]

Is there anything preventing WebAudio from being activated when a mediastream is
attached? The comment says it can't happen, but I don't see how it couldn't.

[mcasas, 2016/03/11 19:40:32]

Done.

+// - a connection between a RestartableAudioRendererSink (the |sink_|) passed in
+//   constructor and an AudioRendererSink::RenderCallback passed on Initialize()
+//   by means of an internal AudioRendererSink::RenderCallback - which also
+//   allows for delivering a copy of the data if a listener is configured.
+// - a connection between the said AudioRendererSink::RenderCallback and a
+//   blink::WebAudioSourceProviderClient passed via setClient() (the |client_|),
+//   again using the internal AudioRendererSink::RenderCallback. Blink calls
+//   provideInput() periodically to fetch the appropriate data.
 //
-// WebAudioSourceProviderImpl wraps an existing audio sink that is used unless
-// WebKit has set a client via setClient(). While a client is set WebKit will
-// periodically call provideInput() to render a certain number of audio
-// sample-frames using the sink's RenderCallback to get the data.
+// WASPImpl is also a RestartableAudioRendererSink itself in order to be
+// controlled (Play(), Pause() etc).
 //
 // All calls are protected by a lock.
 class MEDIA_BLINK_EXPORT WebAudioSourceProviderImpl
     : NON_EXPORTED_BASE(public blink::WebAudioSourceProvider),
       NON_EXPORTED_BASE(public RestartableAudioRendererSink) {
  public:
+  using CopyAudioCB = base::Callback<void(scoped_ptr<AudioBus>,
+                                          uint32_t delay_milliseconds,
+                                          int channels,

[DaleCurtis, 2016/03/11 18:45:59]

Channel count isn't what's necessary, it's the channel layout. You can get the
channel count from the audio_bus.

[mcasas, 2016/03/11 19:40:32]

Done.

Channel layout can be guessed from channel
count right? Using 
GuessChannelLayout(int channels)

[DaleCurtis, 2016/03/12 03:24:42]

No, some layouts will have the same channel count. It's rare, but does happen.
Guessing should only be done when the layout information isn't provided.

+                                          int sample_rate)>;
+
   explicit WebAudioSourceProviderImpl(
       const scoped_refptr<RestartableAudioRendererSink>& sink);
 
@@ -55,36 +65,40 @@ class MEDIA_BLINK_EXPORT WebAudioSourceProviderImpl
   void Initialize(const AudioParameters& params,
                   RenderCallback* renderer) override;
 
- protected:
-  ~WebAudioSourceProviderImpl() override;
+  // These methods allow a client to get a copy of the rendered audio.
+  void RegisterCopyAudioCallback(const CopyAudioCB& callback);
+  void ResetCopyAudioCallback();

[DaleCurtis, 2016/03/11 18:45:59]

Clear?

[mcasas, 2016/03/11 19:40:32]

Done.

 
  private:
+  friend class WebAudioSourceProviderImplTest;
+  ~WebAudioSourceProviderImpl() override;
+
   // Calls setFormat() on |client_| from the Blink renderer thread.
   void OnSetFormat();
 
-  // Closure that posts a task to call OnSetFormat() on the renderer thread.
-  base::Closure set_format_cb_;
+  int RenderForTesting(AudioBus* audio_bus);
 
-  // Set to true when Initialize() is called.
-  int channels_;
-  int sample_rate_;
+  // Used to keep the volume across reconfigurations.
   double volume_;
 
   // Tracks the current playback state.
   enum PlaybackState { kStopped, kStarted, kPlaying };
   PlaybackState state_;
 
-  // Where audio comes from.
-  AudioRendererSink::RenderCallback* renderer_;
-
+  // Closure that calls OnSetFormat() on |client_| on the renderer thread.
+  base::Closure set_format_cb_;
   // When set via setClient() it overrides |sink_| for consuming audio.
   blink::WebAudioSourceProviderClient* client_;
 
   // Where audio ends up unless overridden by |client_|.
   base::Lock sink_lock_;
-  scoped_refptr<RestartableAudioRendererSink> sink_;
+  const scoped_refptr<RestartableAudioRendererSink> sink_;
   scoped_ptr<AudioBus> bus_wrapper_;
 
+  // An inner class acting as a T filter where actual data can be tapped.
+  class TeeFilter;
+  scoped_ptr<TeeFilter> tee_filter_;
+
   // NOTE: Weak pointers must be invalidated before all other member variables.
   base::WeakPtrFactory<WebAudioSourceProviderImpl> weak_factory_;