MediaStream audio sourcing: Bypass audio processing for non-WebRTC cases.

content/renderer/media/media_stream_audio_source.h

Index: content/renderer/media/media_stream_audio_source.h
diff --git a/content/renderer/media/media_stream_audio_source.h b/content/renderer/media/media_stream_audio_source.h
index e332b83e0c8fcb51143f42bf8f3cfecba2b92186..b9d8942c44a3728efc2fc536c93ac55463bca709 100644
--- a/content/renderer/media/media_stream_audio_source.h
+++ b/content/renderer/media/media_stream_audio_source.h
@@ -5,60 +5,180 @@
 #ifndef CONTENT_RENDERER_MEDIA_MEDIA_STREAM_AUDIO_SOURCE_H_
 #define CONTENT_RENDERER_MEDIA_MEDIA_STREAM_AUDIO_SOURCE_H_
 
+#include <vector>
+
 #include "base/compiler_specific.h"
 #include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "base/synchronization/lock.h"
+#include "base/threading/thread_checker.h"
 #include "content/common/content_export.h"
+#include "content/renderer/media/media_stream_audio_track.h"
 #include "content/renderer/media/media_stream_source.h"
 #include "content/renderer/media/webrtc/peer_connection_dependency_factory.h"
 #include "content/renderer/media/webrtc_audio_capturer.h"
+#include "media/base/audio_capturer_source.h"
 #include "third_party/libjingle/source/talk/app/webrtc/mediastreaminterface.h"
 
 namespace content {
 
+// Represents a source of audio, and manages the delivery of audio data between
+// a media::AudioCapturerSource and one or more MediaStreamAudioTracks.  There
+// are three main use cases, corresponding to the three available constructors:
+//
+//   1. Null source: Makes this MediaStreamAudioSource a place-holder
+//      implementation that goes through all the motions, but never transports
+//      any audio data.
+//   2. Local source: Uses content::AudioDeviceFactory to auto-create the
+//      source, using the parameters and session ID found in StreamDeviceInfo,
+//      just before the first track is connected.  Automatically determines
+//      whether to transport audio data directly to the tracks, or to instead
+//      pass it through the WebRTC audio processing pipeline (including
+//      MediaStreamAudioProcessor).
+//   3. Externally-provided local or remote source: Allows users of the public
+//      content::MediaStreamApi to provide a media::AudioCapturerSource to be
+//      used as the source of audio data.  Audio data is transported directly to
+//      the tracks (i.e., there is no audio processing).
+//
+// An instance of this class is owned by blink::WebMediaStreamSource.
 class CONTENT_EXPORT MediaStreamAudioSource

[hubbe, 2016/01/28 21:48:13]

Would it make sense to write this as an abstract class with three different
concrete implementations?

[miu, 2016/01/29 19:43:59]

Good point.  I'll work on this and ping when ready for review again.

-    : NON_EXPORTED_BASE(public MediaStreamSource) {
+    : NON_EXPORTED_BASE(public MediaStreamSource),
+      NON_EXPORTED_BASE(public media::AudioCapturerSource::CaptureCallback) {
  public:
-  MediaStreamAudioSource(int render_frame_id,
-                         const StreamDeviceInfo& device_info,
-                         const SourceStoppedCallback& stop_callback,
-                         PeerConnectionDependencyFactory* factory);
+  // Construct a "null" source (as a place-holder, or for testing).
   MediaStreamAudioSource();
-  ~MediaStreamAudioSource() override;
 
-  void AddTrack(const blink::WebMediaStreamTrack& track,
-                const blink::WebMediaConstraints& constraints,
-                const ConstraintsCallback& callback);
+  // Construct a local source (e.g., microphone or loopback audio capture) of
+  // audio, using the audio parameters found in |device_info|.
+  // |consumer_render_frame_id| references the RenderFrame that will consume the
+  // audio data.  The source is not started until the first call to
+  // ConnectToTrack().
+  MediaStreamAudioSource(int consumer_render_frame_id,
+                         const StreamDeviceInfo& device_info);
+
+  // Construct a source of audio that wraps a media::AudioCapturerSource
+  // implementation.  MediaStreamAudioSource will call the source's Initialize()
+  // and Start/Stop() methods at some point in the future.  Audio will be
+  // provided in the format specified by |sample_rate|, |channel_layout|, and
+  // |frames_per_buffer|.  |is_remote| must be true if the content is being
+  // generated from outside of the application (e.g., audio that is being
+  // streamed from a remote device).  The source is not started until the first
+  // call to ConnectToTrack().
+  MediaStreamAudioSource(
+      const scoped_refptr<media::AudioCapturerSource>& source,
+      int sample_rate,
+      media::ChannelLayout channel_layout,
+      int frames_per_buffer,
+      bool is_remote);
+
+  ~MediaStreamAudioSource() final;
+
+  // To enable WebRTC-specific audio-processing features, this must be called
+  // before the first call to ConnectToTrack().
+  void set_dependency_factory(PeerConnectionDependencyFactory* factory) {
+    pc_factory_ = factory;
+  }
 
+  // Connects this source to the given |track|, creating the appropriate
+  // implementation of the content::MediaStreamAudioTrack interface, which
+  // becomes associated with and owned by |track|.  |constraints| is optional.
+  //
+  // Returns true if the source was successfully started and the
+  // MediaStreamAudioTrack assigned to |track.extraData()|.
+  bool ConnectToTrack(const blink::WebMediaStreamTrack& track,
+                      const blink::WebMediaConstraints& constraints);
+
+  // Getters/Setters to hold references to objects when the WebRTC audio
+  // pipeline is being used.
   void SetLocalAudioSource(webrtc::AudioSourceInterface* source) {
     local_audio_source_ = source;
   }
-
   void SetAudioCapturer(const scoped_refptr<WebRtcAudioCapturer>& capturer) {
     DCHECK(!audio_capturer_.get());
     audio_capturer_ = capturer;
   }
-
   const scoped_refptr<WebRtcAudioCapturer>& GetAudioCapturer() {
     return audio_capturer_;
   }
-
   webrtc::AudioSourceInterface* local_audio_source() {
     return local_audio_source_.get();
   }
 
  protected:
-  void DoStopSource() override;
+  // Called by the superclass to stop whichever source implementation is being
+  // used.
+  void DoStopSource() final;
 
  private:
-  const int render_frame_id_;
-  PeerConnectionDependencyFactory* const factory_;
-
-  // This member holds an instance of webrtc::LocalAudioSource. This is used
-  // as a container for audio options.
+  // Implements the MediaStreamAudioTrack interface, providing the functionality
+  // of adding and removing MediaStreamAudioSinks and delivering audio data to
+  // each; all in a thread-safe manner.
+  //
+  // An instance of this class is owned by blink::WebMediaStreamTrack, but the
+  // AudioTee holds a weak reference to |this| to notify of its destruction.
+  class AudioTee;
+
+  // Determines whether the default audio pipeline or the WebRTC audio pipeline
+  // will be used, and then starts the appropriate source for that pipeline if
+  // needed.  Returns true if the source was successfully started and
+  // MediaStreamAudioTracks can be created and connected to it.
+  bool EnsureSourceIsStarted(const blink::WebMediaConstraints& constraints);
+  void StartDefaultPipeline();
+  void StartWebRtcPipeline(const blink::WebMediaConstraints& constraints);
+
+  // Removes |tee| from the list of instances that get a copy of the source
+  // audio data.
+  void StopAudioDeliveryTo(AudioTee* tee);
+
+  // media::AudioCapturerSource::CaptureCallback implementation.
+  void Capture(const media::AudioBus* audio_bus,
+               int audio_delay_milliseconds,
+               double volume,
+               bool key_pressed) final;
+  void OnCaptureError(const std::string& message) final;
+
+  // The audio parameters to use for |source_|.
+  const media::AudioParameters params_;
+
+  // True if |source_| provides audio data from a remote application.
+  const bool is_remote_;
+
+  // Used when creating AudioInputDevices via the AudioDeviceFactory.
+  const int consumer_render_frame_id_;
+
+  // The current state of this source.
+  enum {
+    NULL_SOURCE_NOT_STARTED,   // This instance is a "null" audio source.

[hubbe, 2016/01/28 21:48:13]

I'm not a big fan of using different states for different types of inputs.
Seems like a mix of purposes.

A single "NOT_STARTED", should be enough I think, and the type of input can
either be represented in a separate variable, or by using one subclass per input
type.

+    INPUT_DEVICE_NOT_STARTED,  // AudioInputDevice not started yet.
+    SOURCE_NOT_STARTED,        // Source provided via ctor not started yet.
+    STARTED_DEFAULT_PIPELINE,  // Started, this instance delivers audio.
+    STARTED_WEBRTC_PIPELINE,   // Started, but using WebRTC audio pipeline.
+    STOPPED,                   // Source stopped.
+  } current_state_;
+
+  // This is lazy-instantiated on the first call to EnsureSourceIsStarted().
+  scoped_refptr<media::AudioCapturerSource> source_;
+
+  // List of currently-connected AudioTees.  This is empty when using the
+  // WebRTC audio pipeline.  While MediaStreamAudioSource creates these
+  // instances, blink::WebMediaStreamTrack instances own the objects.
+  std::vector<AudioTee*> audio_tees_;
+  base::Lock lock_;  // Protects concurrent access to |audio_tees_|.
+
+  // References to WebRTC audio pipeline objects.  These are null, if not
+  // applicable.
+  PeerConnectionDependencyFactory* pc_factory_;  // May be null, if unused.
   scoped_refptr<webrtc::AudioSourceInterface> local_audio_source_;
-
   scoped_refptr<WebRtcAudioCapturer> audio_capturer_;
 
+  // In debug builds, check that all methods that could cause object graph
+  // or data flow changes are being called on the same thread.
+  base::ThreadChecker thread_checker_;
+
+  // Provides weak pointers so that AudioTees can call StopAudioDeliveryTo()
+  // safely.
+  base::WeakPtrFactory<MediaStreamAudioSource> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(MediaStreamAudioSource);
 };