MediaStream audio: Refactor 3 separate "glue" implementations into one.

content/renderer/media/webrtc/processed_local_audio_source.cc

Index: content/renderer/media/webrtc/processed_local_audio_source.cc
diff --git a/content/renderer/media/webrtc_audio_capturer.cc b/content/renderer/media/webrtc/processed_local_audio_source.cc
similarity index 29%
rename from content/renderer/media/webrtc_audio_capturer.cc
rename to content/renderer/media/webrtc/processed_local_audio_source.cc
index 9337756466598745357db83f5d09cca21061eaf4..38e47e155333491c8d9bdf57a74df773d1767b6e 100644
--- a/content/renderer/media/webrtc_audio_capturer.cc
+++ b/content/renderer/media/webrtc/processed_local_audio_source.cc
@@ -2,141 +2,186 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "content/renderer/media/webrtc_audio_capturer.h"
+#include "content/renderer/media/webrtc/processed_local_audio_source.h"
 
-#include "base/bind.h"
 #include "base/logging.h"
-#include "base/macros.h"
 #include "base/metrics/histogram.h"
-#include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
-#include "build/build_config.h"
-#include "content/child/child_process.h"
 #include "content/renderer/media/audio_device_factory.h"
 #include "content/renderer/media/media_stream_audio_processor.h"
 #include "content/renderer/media/media_stream_audio_processor_options.h"
-#include "content/renderer/media/media_stream_audio_source.h"
 #include "content/renderer/media/media_stream_constraints_util.h"
+#include "content/renderer/media/webrtc/peer_connection_dependency_factory.h"
+#include "content/renderer/media/webrtc/processed_local_audio_track.h"
+#include "content/renderer/media/webrtc/webrtc_local_audio_track_adapter.h"
 #include "content/renderer/media/webrtc_audio_device_impl.h"
-#include "content/renderer/media/webrtc_local_audio_track.h"
 #include "content/renderer/media/webrtc_logging.h"
+#include "content/renderer/render_frame_impl.h"
+#include "media/audio/audio_input_device.h"
 #include "media/audio/sample_rates.h"
+#include "media/base/channel_layout.h"
+#include "third_party/webrtc/api/mediaconstraintsinterface.h"
+#include "third_party/webrtc/media/base/mediachannel.h"
 
 namespace content {
 
-// Reference counted container of WebRtcLocalAudioTrack delegate.
-// TODO(xians): Switch to MediaStreamAudioSinkOwner.
-class WebRtcAudioCapturer::TrackOwner
-    : public base::RefCountedThreadSafe<WebRtcAudioCapturer::TrackOwner> {
- public:
-  explicit TrackOwner(WebRtcLocalAudioTrack* track)
-      : delegate_(track) {}
-
-  void Capture(const media::AudioBus& audio_bus,
-               base::TimeTicks estimated_capture_time) {
-    base::AutoLock lock(lock_);
-    if (delegate_) {
-      delegate_->Capture(audio_bus, estimated_capture_time);
-    }
-  }
-
-  void OnSetFormat(const media::AudioParameters& params) {
-    base::AutoLock lock(lock_);
-    if (delegate_)
-      delegate_->OnSetFormat(params);
-  }
+namespace {
+// Used as an identifier for ProcessedLocalAudioSource::From().
+void* const kClassIdentifier = const_cast<void**>(&kClassIdentifier);
+}  // namespace
 
-  void Reset() {
-    base::AutoLock lock(lock_);
-    delegate_ = NULL;
-  }
-
-  void Stop() {
-    base::AutoLock lock(lock_);
-    DCHECK(delegate_);
+ProcessedLocalAudioSource::ProcessedLocalAudioSource(
+    int consumer_render_frame_id,
+    const StreamDeviceInfo& device_info,
+    PeerConnectionDependencyFactory* factory)
+    : MediaStreamAudioSource(true /* is_local_source */),
+      consumer_render_frame_id_(consumer_render_frame_id),
+      pc_factory_(factory),
+      volume_(0),
+      allow_invalid_render_frame_id_for_testing_(false) {
+  DCHECK(pc_factory_);
+  DVLOG(1) << "ProcessedLocalAudioSource::ProcessedLocalAudioSource()";
+  MediaStreamSource::SetDeviceInfo(device_info);
+}
 
-    // This can be reentrant so reset |delegate_| before calling out.
-    WebRtcLocalAudioTrack* temp = delegate_;
-    delegate_ = NULL;
-    temp->Stop();
-  }
+ProcessedLocalAudioSource::~ProcessedLocalAudioSource() {
+  DVLOG(1) << "ProcessedLocalAudioSource::~ProcessedLocalAudioSource()";
+  EnsureSourceIsStopped();
+}
 
-  // Wrapper which allows to use std::find_if() when adding and removing
-  // sinks to/from the list.
-  struct TrackWrapper {
-    explicit TrackWrapper(WebRtcLocalAudioTrack* track) : track_(track) {}
-    bool operator()(
-        const scoped_refptr<WebRtcAudioCapturer::TrackOwner>& owner) const {
-      return owner->IsEqual(track_);
-    }
-    WebRtcLocalAudioTrack* track_;
-  };
+// static
+ProcessedLocalAudioSource* ProcessedLocalAudioSource::From(
+    MediaStreamAudioSource* source) {
+  if (source && source->GetClassIdentifier() == kClassIdentifier)
+    return static_cast<ProcessedLocalAudioSource*>(source);
+  return nullptr;
+}
 
- protected:
-  virtual ~TrackOwner() {}
+void ProcessedLocalAudioSource::SetSourceConstraints(
+    const blink::WebMediaConstraints& constraints) {
+  DCHECK(!constraints.isNull());
+  constraints_ = constraints;
+}
 
- private:
-  friend class base::RefCountedThreadSafe<WebRtcAudioCapturer::TrackOwner>;
+void* ProcessedLocalAudioSource::GetClassIdentifier() const {
+  return kClassIdentifier;
+}
 
-  bool IsEqual(const WebRtcLocalAudioTrack* other) const {
-    base::AutoLock lock(lock_);
-    return (other == delegate_);
-  }
+scoped_ptr<MediaStreamAudioTrack>
+ProcessedLocalAudioSource::CreateMediaStreamAudioTrack(const std::string& id) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  ProcessedLocalAudioTrack* const audio_track = new ProcessedLocalAudioTrack(
+      WebRtcLocalAudioTrackAdapter::Create(id, rtc_source_.get()));
+  audio_track->SetLevel(level_calculator_.level());
+  // The track only grabs stats from the audio processor.  Stats are only
+  // available if audio processing is turned on.  Therefore, only provide the
+  // track a reference if audio processing is turned on.
+  DCHECK(audio_processor_);
+  if (audio_processor_->has_audio_processing())
+    audio_track->SetAudioProcessor(audio_processor_);
+  return scoped_ptr<MediaStreamAudioTrack>(audio_track);
+}
 
-  // Do NOT reference count the |delegate_| to avoid cyclic reference counting.
-  WebRtcLocalAudioTrack* delegate_;
-  mutable base::Lock lock_;
+bool ProcessedLocalAudioSource::EnsureSourceIsStarted() {
+  DCHECK(thread_checker_.CalledOnValidThread());
 
-  DISALLOW_COPY_AND_ASSIGN(TrackOwner);
-};
+  if (source_)
+    return true;
 
-// static
-scoped_ptr<WebRtcAudioCapturer> WebRtcAudioCapturer::CreateCapturer(
-    int render_frame_id,
-    const StreamDeviceInfo& device_info,
-    const blink::WebMediaConstraints& constraints,
-    WebRtcAudioDeviceImpl* audio_device,
-    MediaStreamAudioSource* audio_source) {
-  scoped_ptr<WebRtcAudioCapturer> capturer(new WebRtcAudioCapturer(
-      render_frame_id, device_info, constraints, audio_device, audio_source));
-  if (capturer->Initialize())
-    return capturer;
-
-  return NULL;
-}
+  // Sanity-check that the consuming RenderFrame still exists.  This is
+  // required to initialize the audio source.
+  if (!allow_invalid_render_frame_id_for_testing_ &&
+      !RenderFrameImpl::FromRoutingID(consumer_render_frame_id_)) {
+    WebRtcLogMessage("ProcessedLocalAudioSource::EnsureSourceIsStarted() fails "
+                     " because the render frame does not exist.");
+    return false;
+  }
 
-bool WebRtcAudioCapturer::Initialize() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  DVLOG(1) << "WebRtcAudioCapturer::Initialize()";
   WebRtcLogMessage(base::StringPrintf(
-      "WAC::Initialize. render_frame_id=%d"
+      "ProcessedLocalAudioSource::EnsureSourceIsStarted. render_frame_id=%d"
       ", channel_layout=%d, sample_rate=%d, buffer_size=%d"
       ", session_id=%d, paired_output_sample_rate=%d"
       ", paired_output_frames_per_buffer=%d, effects=%d. ",
-      render_frame_id_, device_info_.device.input.channel_layout,
-      device_info_.device.input.sample_rate,
-      device_info_.device.input.frames_per_buffer, device_info_.session_id,
-      device_info_.device.matched_output.sample_rate,
-      device_info_.device.matched_output.frames_per_buffer,
-      device_info_.device.input.effects));
-
-  if (render_frame_id_ == -1) {
-    // Return true here to allow injecting a new source via
-    // SetCapturerSourceForTesting() at a later state.
-    return true;
+      consumer_render_frame_id_, device_info().device.input.channel_layout,
+      device_info().device.input.sample_rate,
+      device_info().device.input.frames_per_buffer, device_info().session_id,
+      device_info().device.matched_output.sample_rate,
+      device_info().device.matched_output.frames_per_buffer,
+      device_info().device.input.effects));
+
+  // Sanity-check that the constraints, plus the additional input effects are
+  // valid when combined.
+  const MediaAudioConstraints audio_constraints(
+      constraints_, device_info().device.input.effects);
+  if (!audio_constraints.IsValid()) {
+    WebRtcLogMessage("ProcessedLocalAudioSource::EnsureSourceIsStarted() fails "
+                     " because MediaAudioConstraints are not valid.");
+    return false;
   }
 
-  MediaAudioConstraints audio_constraints(constraints_,
-                                          device_info_.device.input.effects);
-  if (!audio_constraints.IsValid())
+  // Build an AudioOptions by applying relevant constraints to it, and then use
+  // it to create a webrtc::AudioSourceInterface instance.
+  cricket::AudioOptions rtc_options;
+  rtc_options.echo_cancellation = ConstraintToOptional(
+      constraints_, &blink::WebMediaTrackConstraintSet::echoCancellation);
+  rtc_options.delay_agnostic_aec = ConstraintToOptional(
+      constraints_, &blink::WebMediaTrackConstraintSet::googDAEchoCancellation);
+  rtc_options.auto_gain_control = ConstraintToOptional(
+      constraints_, &blink::WebMediaTrackConstraintSet::googAutoGainControl);
+  rtc_options.experimental_agc = ConstraintToOptional(
+      constraints_,
+      &blink::WebMediaTrackConstraintSet::googExperimentalAutoGainControl);
+  rtc_options.noise_suppression = ConstraintToOptional(
+      constraints_, &blink::WebMediaTrackConstraintSet::googNoiseSuppression);
+  rtc_options.experimental_ns = ConstraintToOptional(
+      constraints_,
+      &blink::WebMediaTrackConstraintSet::googExperimentalNoiseSuppression);
+  rtc_options.highpass_filter = ConstraintToOptional(
+      constraints_, &blink::WebMediaTrackConstraintSet::googHighpassFilter);
+  rtc_options.typing_detection = ConstraintToOptional(
+      constraints_,
+      &blink::WebMediaTrackConstraintSet::googTypingNoiseDetection);
+  rtc_options.stereo_swapping = ConstraintToOptional(
+      constraints_, &blink::WebMediaTrackConstraintSet::googAudioMirroring);
+  MediaAudioConstraints::ApplyFixedAudioConstraints(&rtc_options);
+  if (device_info().device.input.effects &
+      media::AudioParameters::ECHO_CANCELLER) {
+    // TODO(hta): Figure out if we should be looking at echoCancellation.
+    // Previous code had googEchoCancellation only.
+    const blink::BooleanConstraint& echoCancellation =
+        constraints_.basic().googEchoCancellation;
+    if (echoCancellation.hasExact() && !echoCancellation.exact()) {
+      StreamDeviceInfo modified_device_info(device_info());
+      modified_device_info.device.input.effects &=
+          ~media::AudioParameters::ECHO_CANCELLER;
+      SetDeviceInfo(modified_device_info);
+    }
+    rtc_options.echo_cancellation = rtc::Optional<bool>(false);
+  }
+  rtc_source_ = pc_factory_->CreateLocalAudioSource(rtc_options);
+  if (rtc_source_->state() != webrtc::MediaSourceInterface::kLive) {
+    WebRtcLogMessage("ProcessedLocalAudioSource::EnsureSourceIsStarted() fails "
+                     " because the rtc LocalAudioSource is not live.");
     return false;
+  }
 
-  media::ChannelLayout channel_layout = static_cast<media::ChannelLayout>(
-      device_info_.device.input.channel_layout);
+  // Create the MediaStreamAudioProcessor, bound to the WebRTC audio device
+  // module.
+  WebRtcAudioDeviceImpl* const rtc_audio_device =
+      pc_factory_->GetWebRtcAudioDevice();
+  if (!rtc_audio_device) {
+    WebRtcLogMessage("ProcessedLocalAudioSource::EnsureSourceIsStarted() fails "
+                     " because there is no WebRtcAudioDeviceImpl instance.");
+    return false;
+  }
+  audio_processor_ = new rtc::RefCountedObject<MediaStreamAudioProcessor>(
+      constraints_, device_info().device.input, rtc_audio_device);
 
   // If KEYBOARD_MIC effect is set, change the layout to the corresponding
   // layout that includes the keyboard mic.
-  if ((device_info_.device.input.effects &
+  media::ChannelLayout channel_layout = static_cast<media::ChannelLayout>(
+      device_info().device.input.channel_layout);
+  if ((device_info().device.input.effects &
        media::AudioParameters::KEYBOARD_MIC) &&
       audio_constraints.GetGoogExperimentalNoiseSuppression()) {
     if (channel_layout == media::CHANNEL_LAYOUT_STEREO) {
@@ -157,282 +202,101 @@ bool WebRtcAudioCapturer::Initialize() {
   if (channel_layout != media::CHANNEL_LAYOUT_MONO &&
       channel_layout != media::CHANNEL_LAYOUT_STEREO &&
       channel_layout != media::CHANNEL_LAYOUT_STEREO_AND_KEYBOARD_MIC) {
-    DLOG(ERROR) << channel_layout
-                << " is not a supported input channel configuration.";
+    WebRtcLogMessage(base::StringPrintf(
+        "ProcessedLocalAudioSource::EnsureSourceIsStarted() fails "
+        " because the input channel layout (%d) is not supported.",
+        static_cast<int>(channel_layout)));
     return false;
   }
 
   DVLOG(1) << "Audio input hardware sample rate: "
-           << device_info_.device.input.sample_rate;
+           << device_info().device.input.sample_rate;
   media::AudioSampleRate asr;
-  if (media::ToAudioSampleRate(device_info_.device.input.sample_rate, &asr)) {
+  if (media::ToAudioSampleRate(device_info().device.input.sample_rate, &asr)) {
     UMA_HISTOGRAM_ENUMERATION(
         "WebRTC.AudioInputSampleRate", asr, media::kAudioSampleRateMax + 1);
   } else {
     UMA_HISTOGRAM_COUNTS("WebRTC.AudioInputSampleRateUnexpected",
-                         device_info_.device.input.sample_rate);
+                         device_info().device.input.sample_rate);
   }
 
-  // Create and configure the default audio capturing source.
-  SetCapturerSourceInternal(
-      AudioDeviceFactory::NewInputDevice(render_frame_id_), channel_layout,
-      device_info_.device.input.sample_rate);
+  // Determine the audio format required of the AudioCapturerSource.  Then, pass
+  // that to the |audio_processor_| and set the output format of this
+  // ProcessedLocalAudioSource to the processor's output format.
+  media::AudioParameters params(
+      media::AudioParameters::AUDIO_PCM_LOW_LATENCY, channel_layout,
+      device_info().device.input.sample_rate, 16,
+      GetBufferSize(device_info().device.input.sample_rate));
+  params.set_effects(device_info().device.input.effects);
+  DCHECK(params.IsValid());
+  audio_processor_->OnCaptureFormatChanged(params);
+  MediaStreamAudioSource::SetFormat(audio_processor_->OutputFormat());
+
+  // Start the source.
+  VLOG(1) << "Starting WebRTC audio source for consumption by render frame "
+          << consumer_render_frame_id_ << " with input parameters={"
+          << params.AsHumanReadableString() << "} and output parameters={"
+          << GetAudioParameters().AsHumanReadableString() << '}';
+  source_ = AudioDeviceFactory::NewInputDevice(consumer_render_frame_id_);
+  source_->Initialize(params, this, device_info().session_id);
+  // We need to set the AGC control before starting the stream.
+  source_->SetAutomaticGainControl(true);
+  source_->Start();
 
-  // Add the capturer to the WebRtcAudioDeviceImpl since it needs some hardware
-  // information from the capturer.
-  if (audio_device_)
-    audio_device_->AddAudioCapturer(this);
+  // Register this source with the WebRtcAudioDeviceImpl.
+  rtc_audio_device->AddAudioCapturer(this);
 
   return true;
 }
 
-WebRtcAudioCapturer::WebRtcAudioCapturer(
-    int render_frame_id,
-    const StreamDeviceInfo& device_info,
-    const blink::WebMediaConstraints& constraints,
-    WebRtcAudioDeviceImpl* audio_device,
-    MediaStreamAudioSource* audio_source)
-    : constraints_(constraints),
-      audio_processor_(new rtc::RefCountedObject<MediaStreamAudioProcessor>(
-          constraints,
-          device_info.device.input,
-          audio_device)),
-      running_(false),
-      render_frame_id_(render_frame_id),
-      device_info_(device_info),
-      volume_(0),
-      peer_connection_mode_(false),
-      audio_device_(audio_device),
-      audio_source_(audio_source) {
-  DVLOG(1) << "WebRtcAudioCapturer::WebRtcAudioCapturer()";
-}
-
-WebRtcAudioCapturer::~WebRtcAudioCapturer() {
+void ProcessedLocalAudioSource::EnsureSourceIsStopped() {
   DCHECK(thread_checker_.CalledOnValidThread());
-  DCHECK(tracks_.IsEmpty());
-  DVLOG(1) << "WebRtcAudioCapturer::~WebRtcAudioCapturer()";
-  Stop();
-}
-
-void WebRtcAudioCapturer::AddTrack(WebRtcLocalAudioTrack* track) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  DCHECK(track);
-  DVLOG(1) << "WebRtcAudioCapturer::AddTrack()";
-
-  track->SetLevel(level_calculator_.level());
 
-  // The track only grabs stats from the audio processor.  Stats are only
-  // available if audio processing is turned on.  Therefore, only provide the
-  // track a reference if audio processing is turned on.
-  if (audio_processor_->has_audio_processing())
-    track->SetAudioProcessor(audio_processor_);
-
-  {
-    base::AutoLock auto_lock(lock_);
-    // Verify that |track| is not already added to the list.
-    DCHECK(!tracks_.Contains(TrackOwner::TrackWrapper(track)));
-
-    // Add with a tag, so we remember to call OnSetFormat() on the new
-    // track.
-    scoped_refptr<TrackOwner> track_owner(new TrackOwner(track));
-    tracks_.AddAndTag(track_owner.get());
-  }
-}
-
-void WebRtcAudioCapturer::RemoveTrack(WebRtcLocalAudioTrack* track) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  DVLOG(1) << "WebRtcAudioCapturer::RemoveTrack()";
-  bool stop_source = false;
-  {
-    base::AutoLock auto_lock(lock_);
-
-    scoped_refptr<TrackOwner> removed_item =
-        tracks_.Remove(TrackOwner::TrackWrapper(track));
-
-    // Clear the delegate to ensure that no more capture callbacks will
-    // be sent to this sink. Also avoids a possible crash which can happen
-    // if this method is called while capturing is active.
-    if (removed_item.get()) {
-      removed_item->Reset();
-      stop_source = tracks_.IsEmpty();
-    }
-  }
-  if (stop_source) {
-    // Since WebRtcAudioCapturer does not inherit MediaStreamAudioSource,
-    // and instead MediaStreamAudioSource is composed of a WebRtcAudioCapturer,
-    // we have to call StopSource on the MediaStreamSource. This will call
-    // MediaStreamAudioSource::DoStopSource which in turn call
-    // WebRtcAudioCapturerer::Stop();
-    audio_source_->StopSource();
-  }
-}
-
-void WebRtcAudioCapturer::SetCapturerSourceInternal(
-    const scoped_refptr<media::AudioCapturerSource>& source,
-    media::ChannelLayout channel_layout,
-    int sample_rate) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  DVLOG(1) << "SetCapturerSource(channel_layout=" << channel_layout << ","
-           << "sample_rate=" << sample_rate << ")";
-  scoped_refptr<media::AudioCapturerSource> old_source;
-  {
-    base::AutoLock auto_lock(lock_);
-    if (source_.get() == source.get())
-      return;
-
-    source_.swap(old_source);
-    source_ = source;
-
-    // Reset the flag to allow starting the new source.
-    running_ = false;
-  }
-
-  DVLOG(1) << "Switching to a new capture source.";
-  if (old_source.get())
-    old_source->Stop();
-
-  // Dispatch the new parameters both to the sink(s) and to the new source,
-  // also apply the new |constraints|.
-  // The idea is to get rid of any dependency of the microphone parameters
-  // which would normally be used by default.
-  // bits_per_sample is always 16 for now.
-  media::AudioParameters params(media::AudioParameters::AUDIO_PCM_LOW_LATENCY,
-                                channel_layout, sample_rate, 16,
-                                GetBufferSize(sample_rate));
-  params.set_effects(device_info_.device.input.effects);
-  DCHECK(params.IsValid());
-
-  {
-    base::AutoLock auto_lock(lock_);
-
-    // Notify the |audio_processor_| of the new format.  We're doing this while
-    // the lock is held only because the signaling thread might be calling
-    // GetInputFormat().  Simultaneous reads from the audio thread are NOT the
-    // concern here since the source is currently stopped (i.e., no audio
-    // capture calls can be executing).
-    audio_processor_->OnCaptureFormatChanged(params);
-
-    // Notify all tracks about the new format.
-    tracks_.TagAll();
-  }
-
-  if (source.get())
-    source->Initialize(params, this, device_info_.session_id);
-
-  Start();
-}
-
-void WebRtcAudioCapturer::EnablePeerConnectionMode() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  DVLOG(1) << "EnablePeerConnectionMode";
-  // Do nothing if the peer connection mode has been enabled.
-  if (peer_connection_mode_)
+  if (!source_)

[perkj_chrome, 2016/04/08 14:05:42]

can source_ really be null? looks like that can only happen if
EnsureSourceIsStarted has not been called or EnsureSourceIsStopped() is called
twice. 
Can you add a comment if EnsureSourceIsStopped() can be called twice? 

[miu, 2016/04/19 00:40:22]

Ack.  (EnsureSourceIsStopped() shouldn't be called twice.)

     return;
 
-  peer_connection_mode_ = true;
-  int render_frame_id = -1;
-  media::AudioParameters input_params;
-  {
-    base::AutoLock auto_lock(lock_);
-    // Simply return if there is no existing source or the |render_frame_id_| is
-    // not valid.
-    if (!source_.get() || render_frame_id_ == -1)
-      return;
-
-    render_frame_id = render_frame_id_;
-    input_params = audio_processor_->InputFormat();
-  }
-
-  // Do nothing if the current buffer size is the WebRtc native buffer size.
-  if (GetBufferSize(input_params.sample_rate()) ==
-          input_params.frames_per_buffer()) {
-    return;
+  if (WebRtcAudioDeviceImpl* rtc_audio_device =
+      pc_factory_->GetWebRtcAudioDevice()) {
+    rtc_audio_device->RemoveAudioCapturer(this);
   }
 
-  // Create a new audio stream as source which will open the hardware using
-  // WebRtc native buffer size.
-  SetCapturerSourceInternal(AudioDeviceFactory::NewInputDevice(render_frame_id),
-                            input_params.channel_layout(),
-                            input_params.sample_rate());
-}
-
-void WebRtcAudioCapturer::Start() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  DVLOG(1) << "WebRtcAudioCapturer::Start()";
-  base::AutoLock auto_lock(lock_);
-  if (running_ || !source_.get())
-    return;
-
-  // Start the data source, i.e., start capturing data from the current source.
-  // We need to set the AGC control before starting the stream.
-  source_->SetAutomaticGainControl(true);
-  source_->Start();
-  running_ = true;
-}
-
-void WebRtcAudioCapturer::Stop() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  DVLOG(1) << "WebRtcAudioCapturer::Stop()";
-  scoped_refptr<media::AudioCapturerSource> source;
-  TrackList::ItemList tracks;
+  // Note: Stopping the source while holding the |volume_lock_| because the
+  // SetVolume() method needs to know whether |source_| is valid.
   {
-    base::AutoLock auto_lock(lock_);
-    if (!running_)
-      return;
-
-    source = source_;
-    tracks = tracks_.Items();
-    tracks_.Clear();
-    running_ = false;
+    base::AutoLock auto_lock(volume_lock_);
+    source_->Stop();
+    source_ = nullptr;
   }
 
-  // Remove the capturer object from the WebRtcAudioDeviceImpl.
-  if (audio_device_)
-    audio_device_->RemoveAudioCapturer(this);
-
-  for (TrackList::ItemList::const_iterator it = tracks.begin();
-       it != tracks.end();
-       ++it) {
-    (*it)->Stop();
-  }
-
-  if (source.get())
-    source->Stop();
-
   // Stop the audio processor to avoid feeding render data into the processor.
   audio_processor_->Stop();
+
+  VLOG(1) << "Stopped WebRTC audio pipeline for consumption by render frame "
+          << consumer_render_frame_id_ << '.';
 }
 
-void WebRtcAudioCapturer::SetVolume(int volume) {
-  DVLOG(1) << "WebRtcAudioCapturer::SetVolume()";
+void ProcessedLocalAudioSource::SetVolume(int volume) {
+  DVLOG(1) << "ProcessedLocalAudioSource::SetVolume()";
   DCHECK_LE(volume, MaxVolume());
   double normalized_volume = static_cast<double>(volume) / MaxVolume();
-  base::AutoLock auto_lock(lock_);
-  if (source_.get())
+  base::AutoLock auto_lock(volume_lock_);
+  if (source_)
     source_->SetVolume(normalized_volume);
 }
 
-int WebRtcAudioCapturer::Volume() const {
-  base::AutoLock auto_lock(lock_);
+int ProcessedLocalAudioSource::Volume() const {
+  base::AutoLock auto_lock(volume_lock_);
   return volume_;
 }
 
-int WebRtcAudioCapturer::MaxVolume() const {
+int ProcessedLocalAudioSource::MaxVolume() const {
   return WebRtcAudioDeviceImpl::kMaxVolumeLevel;
 }
 
-media::AudioParameters WebRtcAudioCapturer::GetOutputFormat() const {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  return audio_processor_->OutputFormat();
-}
-
-void WebRtcAudioCapturer::Capture(const media::AudioBus* audio_source,
-                                  int audio_delay_milliseconds,
-                                  double volume,
-                                  bool key_pressed) {
-// This callback is driven by AudioInputDevice::AudioThreadCallback if
-// |source_| is AudioInputDevice, otherwise it is driven by client's
-// CaptureCallback.
+void ProcessedLocalAudioSource::Capture(const media::AudioBus* audio_bus,
+                                        int audio_delay_milliseconds,
+                                        double volume,
+                                        bool key_pressed) {
 #if defined(OS_WIN) || defined(OS_MACOSX)
   DCHECK_LE(volume, 1.0);
 #elif (defined(OS_LINUX) && !defined(OS_CHROMEOS)) || defined(OS_OPENBSD)
@@ -449,22 +313,15 @@ void WebRtcAudioCapturer::Capture(const media::AudioBus* audio_source,
   // audio/video sync.  http://crbug.com/335335
   const base::TimeTicks reference_clock_snapshot = base::TimeTicks::Now();
 
-  TrackList::ItemList tracks;
-  TrackList::ItemList tracks_to_notify_format;
-  int current_volume = 0;
+  // Map internal volume range of [0.0, 1.0] into [0, 255] used by AGC.
+  // The volume can be higher than 255 on Linux, and it will be cropped to
+  // 255 since AGC does not allow values out of range.
+  int current_volume = static_cast<int>((volume * MaxVolume()) + 0.5);
   {
-    base::AutoLock auto_lock(lock_);
-    if (!running_)
-      return;
-
-    // Map internal volume range of [0.0, 1.0] into [0, 255] used by AGC.
-    // The volume can be higher than 255 on Linux, and it will be cropped to
-    // 255 since AGC does not allow values out of range.
-    volume_ = static_cast<int>((volume * MaxVolume()) + 0.5);
-    current_volume = volume_ > MaxVolume() ? MaxVolume() : volume_;
-    tracks = tracks_.Items();
-    tracks_.RetrieveAndClearTags(&tracks_to_notify_format);
+    base::AutoLock auto_lock(volume_lock_);
+    volume_ = current_volume;
   }
+  current_volume = volume_ > MaxVolume() ? MaxVolume() : volume_;
 
   // Sanity-check the input audio format in debug builds.  Then, notify the
   // tracks if the format has changed.
@@ -473,25 +330,18 @@ void WebRtcAudioCapturer::Capture(const media::AudioBus* audio_source,
   // because the audio processor format changes only occur while audio capture
   // is stopped.
   DCHECK(audio_processor_->InputFormat().IsValid());
-  DCHECK_EQ(audio_source->channels(),
-            audio_processor_->InputFormat().channels());
-  DCHECK_EQ(audio_source->frames(),
+  DCHECK_EQ(audio_bus->channels(), audio_processor_->InputFormat().channels());
+  DCHECK_EQ(audio_bus->frames(),
             audio_processor_->InputFormat().frames_per_buffer());
-  if (!tracks_to_notify_format.empty()) {
-    const media::AudioParameters& output_params =
-        audio_processor_->OutputFormat();
-    for (const auto& track : tracks_to_notify_format)
-      track->OnSetFormat(output_params);
-  }
 
   // Figure out if the pre-processed data has any energy or not. This
   // information will be passed to the level calculator to force it to report
   // energy in case the post-processed data is zeroed by the audio processing.
-  const bool force_report_nonzero_energy = !audio_source->AreFramesZero();
+  const bool force_report_nonzero_energy = !audio_bus->AreFramesZero();
 
   // Push the data to the processor for processing.
   audio_processor_->PushCaptureData(
-      *audio_source,
+      *audio_bus,
       base::TimeDelta::FromMilliseconds(audio_delay_milliseconds));
 
   // Process and consume the data in the processor until there is not enough
@@ -506,10 +356,8 @@ void WebRtcAudioCapturer::Capture(const media::AudioBus* audio_source,
 
     level_calculator_.Calculate(*processed_data, force_report_nonzero_energy);
 
-    const base::TimeTicks processed_data_capture_time =
-        reference_clock_snapshot - processed_data_audio_delay;
-    for (const auto& track : tracks)
-      track->Capture(*processed_data, processed_data_capture_time);
+    MediaStreamAudioSource::DeliverDataToTracks(
+        *processed_data, reference_clock_snapshot - processed_data_audio_delay);
 
     if (new_volume) {
       SetVolume(new_volume);
@@ -520,47 +368,39 @@ void WebRtcAudioCapturer::Capture(const media::AudioBus* audio_source,
   }
 }
 
-void WebRtcAudioCapturer::OnCaptureError(const std::string& message) {
-  WebRtcLogMessage("WAC::OnCaptureError: " + message);
+void ProcessedLocalAudioSource::OnCaptureError(const std::string& message) {
+  WebRtcLogMessage("ProcessedLocalAudioSource::OnCaptureError: " + message);
 }
 
-media::AudioParameters WebRtcAudioCapturer::GetInputFormat() const {
-  base::AutoLock auto_lock(lock_);
-  return audio_processor_->InputFormat();
+media::AudioParameters ProcessedLocalAudioSource::GetInputFormat() const {
+  return audio_processor_ ? audio_processor_->InputFormat()
+                          : media::AudioParameters();
 }
 
-int WebRtcAudioCapturer::GetBufferSize(int sample_rate) const {
+int ProcessedLocalAudioSource::GetBufferSize(int sample_rate) const {
   DCHECK(thread_checker_.CalledOnValidThread());
 #if defined(OS_ANDROID)
-  // TODO(henrika): Tune and adjust buffer size on Android.
+  // TODO(henrika): Re-evaluate whether to use same logic as other platforms.
   return (2 * sample_rate / 100);
 #endif
 
-  // PeerConnection is running at a buffer size of 10ms data. A multiple of
-  // 10ms as the buffer size can give the best performance to PeerConnection.
-  int peer_connection_buffer_size = sample_rate / 100;
-
-  // Use the native hardware buffer size in non peer connection mode when the
-  // platform is using a native buffer size smaller than the PeerConnection
-  // buffer size and audio processing is off.
-  int hardware_buffer_size = device_info_.device.input.frames_per_buffer;
-  if (!peer_connection_mode_ && hardware_buffer_size &&
-      hardware_buffer_size <= peer_connection_buffer_size &&
-      !audio_processor_->has_audio_processing()) {
-    DVLOG(1) << "WebRtcAudioCapturer is using hardware buffer size "
-             << hardware_buffer_size;
-    return hardware_buffer_size;
-  }
+  // If audio processing is turned on, require 10ms buffers.
+  if (audio_processor_->has_audio_processing())
+    return (sample_rate / 100);
 
-  return (sample_rate / 100);
-}
+  // If audio processing is off and the native hardware buffer size was
+  // provided, use it.  It can be harmful, in terms of CPU/power consumption, to
+  // use smaller buffer sizes than the native size (http://crbug.com/362261).
+  if (int hardware_buffer_size = device_info().device.input.frames_per_buffer)
+    return hardware_buffer_size;
 
-void WebRtcAudioCapturer::SetCapturerSource(
-    const scoped_refptr<media::AudioCapturerSource>& source,
-    media::AudioParameters params) {
-  // Create a new audio stream as source which uses the new source.
-  SetCapturerSourceInternal(source, params.channel_layout(),
-                            params.sample_rate());
+  // If the buffer size is missing from the StreamDeviceInfo, provide a
+  // reasonable default.  Guidance: http://crbug.com/362261, and the current
+  // default in src/media/audio/... for most platforms (as of Mar 2016).
+  //
+  // TODO(miu): Identify where/why the buffer size might be missing, fix the
+  // code, and then require it here.
+  return 1024;
 }
 
 }  // namespace content