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..a817a3c57990112ac2a579956343084d8bdb855a 100644
--- a/media/blink/webaudiosourceprovider_impl.h
+++ b/media/blink/webaudiosourceprovider_impl.h
@@ -24,19 +24,27 @@ class WebAudioSourceProviderClient;
 
 namespace media {
 
-// WebAudioSourceProviderImpl provides a bridge between classes:
-//     blink::WebAudioSourceProvider <---> AudioRendererSink
-//
-// 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.
+// WebAudioSourceProviderImpl is either one of two things:
+// - a connection between a RestartableAudioRendererSink passed in constructor
+//   and an AudioRendererSink::RenderCallback passed on Initialize(), by being
+//   itself a forwarding AudioRendererSink::RenderCallback - which also
+//   eavesdrops if listeners are configured.
+// - a connection between the said AudioRendererSink::RenderCallback and a
+//   blink::WebAudioSourceProviderClient passed via setClient(), by being itself
+//   a blink::WebAudioSourceProvider. Blink calls provideInput() periodically
+//   to fetch the appropriate data.
+// Finally, WASPImpl is also a RestartableAudioRendererSink to be controlled by
+// an AudioRenderer (which happens to be our AudioRendererSink::RenderCallback).
 //
 // All calls are protected by a lock.
 class MEDIA_BLINK_EXPORT WebAudioSourceProviderImpl
     : NON_EXPORTED_BASE(public blink::WebAudioSourceProvider),
-      NON_EXPORTED_BASE(public RestartableAudioRendererSink) {
+      NON_EXPORTED_BASE(public RestartableAudioRendererSink),
+      NON_EXPORTED_BASE(public AudioRendererSink::RenderCallback) {

[DaleCurtis, 2016/03/11 01:41:42]

Instead of inheriting from this can you create a new RenderCallbackCopier
(naming up to you) which WASPI can own that implements the RenderCallback
interface? This allows to prevent further inheritance bloat by this class.

[mcasas, 2016/03/11 04:06:23]

I think is messier but done.

Called the inner thing TeeFilter which is quite
understandable, otherwise please suggest.

  public:
+  using OnAudioBusCB =

[DaleCurtis, 2016/03/11 01:41:42]

OnAudioBusCB is a bit specific. How about something like CopyAudioCB? This also
needs the sample rate of the audio at least. Probably you'll want the channel
layout too, but could add that later.

[mcasas, 2016/03/11 04:06:23]

Done
Why wait? Now that I've got some review 
time I'd rather add that too ;)

+      base::Callback<void(scoped_ptr<AudioBus>, uint32_t delay_milliseconds)>;
+
   explicit WebAudioSourceProviderImpl(
       const scoped_refptr<RestartableAudioRendererSink>& sink);
 
@@ -53,7 +61,18 @@ class MEDIA_BLINK_EXPORT WebAudioSourceProviderImpl
   bool SetVolume(double volume) override;
   OutputDevice* GetOutputDevice() override;
   void Initialize(const AudioParameters& params,
-                  RenderCallback* renderer) override;
+                  AudioRendererSink::RenderCallback* renderer) override;
+
+  // AudioRendererSink::RenderCallback implementation.
+  // These are forwarders to |renderer_| and are here to allow for a client to
+  // get a copy of the rendered audio by RegisterOnAudioBusCallback().
+  int Render(AudioBus* audio_bus,
+             uint32_t delay_milliseconds,
+             uint32_t frames_skipped) override;
+  void OnRenderError() override;
+
+  void RegisterOnAudioBusCallback(const OnAudioBusCB& callback);
+  void ResetOnAudioBusCallback();
 
  protected:
   ~WebAudioSourceProviderImpl() override;
@@ -85,7 +104,11 @@ class MEDIA_BLINK_EXPORT WebAudioSourceProviderImpl
   scoped_refptr<RestartableAudioRendererSink> sink_;
   scoped_ptr<AudioBus> bus_wrapper_;
 
+  OnAudioBusCB onaudiobus_callback_;
+
   // NOTE: Weak pointers must be invalidated before all other member variables.
+  // TODO(mcasas): This class is ref-counted via (Restartable)AudioRendererSink.
+  // and that does not seem to go well with this.
   base::WeakPtrFactory<WebAudioSourceProviderImpl> weak_factory_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(WebAudioSourceProviderImpl);