Unmute Tab Audio For Desktop Share By Default

content/browser/renderer_host/media/audio_input_renderer_host.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/browser/renderer_host/media/audio_input_renderer_host.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/files/file.h"
@@ skipping 418 matching lines @@
   if (!writer->Init()) {
     SendErrorMessage(stream_id, SYNC_WRITER_INIT_FAILED);
     MaybeUnregisterKeyboardMicStream(config);
     return;
   }
 
   // If we have successfully created the SyncWriter then assign it to the
   // entry and construct an AudioInputController.
   entry->writer.reset(writer.release());
   if (WebContentsMediaCaptureId::IsWebContentsDeviceId(device_id)) {
+    // For MEDIA_DESKTOP_AUDIO_CAPTURE, the source is selected from picker
+    // window, we do not mute the source audio.
+    // For MEDIA_TAB_AUDIO_CAPTURE, the probable use case is Cast, we mute
+    // the source audio.
+    // TODO(qiangchen): Analyze audio constraints to make a duplicating or
+    // diverting decision. It would give web developer more flexibility.
     entry->controller = media::AudioInputController::CreateForStream(
         audio_manager_->GetTaskRunner(),
         this,
         WebContentsAudioInputStream::Create(
             device_id,
             audio_params,
             audio_manager_->GetWorkerTaskRunner(),
-            audio_mirroring_manager_),
+            audio_mirroring_manager_,
+            type == MEDIA_DESKTOP_AUDIO_CAPTURE),
         entry->writer.get(),
         user_input_monitor_);
     // Only count for captures from desktop media picker dialog.
     if (entry->controller.get() && type == MEDIA_DESKTOP_AUDIO_CAPTURE)
       IncrementDesktopCaptureCounter(TAB_AUDIO_CAPTURER_CREATED);
   } else {
     // We call CreateLowLatency regardless of the value of
     // |audio_params.format|. Low latency can currently mean different things in
     // different parts of the stack.
     // TODO(grunell): Clean up the low latency terminology so that it's less
@@ skipping 272 matching lines @@
   if (entry->input_debug_writer.get()) {
     BrowserThread::PostTask(
         BrowserThread::FILE, FROM_HERE,
         base::Bind(&DeleteInputDebugWriterOnFileThread,
                    base::Passed(std::move(entry->input_debug_writer))));
   }
 }
 #endif  // defined(ENABLE_WEBRTC)
 
 }  // namespace content