Use LocalMediaStreamAudioSource for screen-casting use cases.

content/renderer/media/user_media_client_impl.cc

 // 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.
 
 #include "content/renderer/media/user_media_client_impl.h"
 
 #include <stddef.h>
 
 #include <utility>
 #include <vector>
 
 #include "base/hash.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "content/public/renderer/render_frame.h"
+#include "content/renderer/media/local_media_stream_audio_source.h"
 #include "content/renderer/media/media_stream.h"
 #include "content/renderer/media/media_stream_constraints_util.h"
 #include "content/renderer/media/media_stream_dispatcher.h"
 #include "content/renderer/media/media_stream_video_capturer_source.h"
 #include "content/renderer/media/media_stream_video_track.h"
 #include "content/renderer/media/peer_connection_tracker.h"
 #include "content/renderer/media/webrtc/processed_local_audio_source.h"
 #include "content/renderer/media/webrtc/webrtc_video_capturer_adapter.h"
 #include "content/renderer/media/webrtc_logging.h"
 #include "content/renderer/media/webrtc_uma_histograms.h"
@@ skipping 601 matching lines @@
         base::Bind(&UserMediaClientImpl::OnLocalSourceStopped,
                    weak_factory_.GetWeakPtr()));
     webkit_source->setExtraData(audio_source);  // Takes ownership.
   }
   local_sources_.push_back(*webkit_source);
 }
 
 MediaStreamAudioSource* UserMediaClientImpl::CreateAudioSource(
     const StreamDeviceInfo& device,
     const blink::WebMediaConstraints& constraints) {
-  // TODO(miu): In a soon-upcoming change, I'll be providing an alternative
-  // MediaStreamAudioSource that bypasses audio processing for the non-WebRTC
-  // use cases. http://crbug.com/577881
+  // If the audio device is a loopback device (for screen capture), or if the
+  // constraints/effects parameters indicate no audio processing is needed,
+  // create an efficient, direct-path MediaStreamAudioSource instance.
+  if (IsScreenCaptureMediaType(device.device.type) ||
+      !MediaStreamAudioProcessor::WouldModifyAudio(
+          constraints, device.device.input.effects)) {
+    return new LocalMediaStreamAudioSource(RenderFrameObserver::routing_id(),
+                                           device);
+  }
+
+  // The audio device is not associated with screen capture and also requires
+  // processing.
   ProcessedLocalAudioSource* source = new ProcessedLocalAudioSource(
       RenderFrameObserver::routing_id(), device, dependency_factory_);
   source->SetSourceConstraints(constraints);
   return source;
 }
 
 MediaStreamVideoSource* UserMediaClientImpl::CreateVideoSource(
     const StreamDeviceInfo& device,
     const MediaStreamSource::SourceStoppedCallback& stop_callback) {
   content::MediaStreamVideoCapturerSource* ret =
@@ skipping 528 matching lines @@
 
 bool UserMediaClientImpl::UserMediaRequestInfo::HasPendingSources() const {
   return !sources_waiting_for_callback_.empty();
 }
 
 void UserMediaClientImpl::OnDestruct() {
   delete this;
 }
 
 }  // namespace content