Browser-wide audio mirroring for TabCapture API

media/audio/virtual_audio_output_stream.cc

Index: media/audio/virtual_audio_output_stream.cc
diff --git a/media/audio/virtual_audio_output_stream.cc b/media/audio/virtual_audio_output_stream.cc
new file mode 100644
index 0000000000000000000000000000000000000000..03b72cf092d9360a67a204f79ad517d726686f2c
--- /dev/null
+++ b/media/audio/virtual_audio_output_stream.cc
@@ -0,0 +1,83 @@
+// 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 "media/audio/virtual_audio_output_stream.h"
+
+#include "base/message_loop.h"
+#include "media/audio/audio_manager_base.h"
+#include "media/audio/virtual_audio_input_stream.h"
+
+namespace media {
+
+// static
+VirtualAudioOutputStream* VirtualAudioOutputStream::MakeStream(
+    AudioManagerBase* manager, const AudioParameters& params,
+    VirtualAudioInputStream* target) {
+  return new VirtualAudioOutputStream(manager, params, target);
+}
+
+VirtualAudioOutputStream::VirtualAudioOutputStream(
+    AudioManagerBase* manager, const AudioParameters& params,
+    VirtualAudioInputStream* target)
+    : audio_manager_(manager), callback_(NULL), params_(params),
+      target_input_stream_(target), volume_(1.0f), attached_(false) {
+}
+
+VirtualAudioOutputStream::~VirtualAudioOutputStream() {
+  DCHECK(!callback_);
+  DCHECK(!attached_);
+}
+
+bool VirtualAudioOutputStream::Open() {
+  DCHECK(CalledOnAudioThread());
+  return true;
+}
+
+void VirtualAudioOutputStream::Start(AudioSourceCallback* callback)  {
+  DCHECK(CalledOnAudioThread());
+  DCHECK(!attached_);
+  callback_ = callback;
+  target_input_stream_->AddOutputStream(this, params_);
+  attached_ = true;
+}
+
+void VirtualAudioOutputStream::Stop() {
+  DCHECK(CalledOnAudioThread());
+  DCHECK(attached_);
+  callback_ = NULL;
+  target_input_stream_->RemoveOutputStream(this, params_);
+  attached_ = false;
+}
+
+void VirtualAudioOutputStream::Close() {
+  DCHECK(CalledOnAudioThread());
+  audio_manager_->ReleaseOutputStream(this);
+}
+
+void VirtualAudioOutputStream::SetVolume(double volume) {
+  volume_ = static_cast<float>(volume);

[DaleCurtis, 2012/12/03 19:27:28]

Change class variable to double instead?

[justinlin, 2012/12/03 21:18:42]

Done.

+}
+
+void VirtualAudioOutputStream::GetVolume(double* volume) {
+  *volume = volume_;
+}
+
+double VirtualAudioOutputStream::ProvideInput(
+    AudioBus* audio_bus, base::TimeDelta buffer_delay) {
+  DCHECK(CalledOnAudioThread());
+  if (!callback_)

[DaleCurtis, 2012/12/03 19:27:28]

I'd just DCHECK(callback_) or CHECK() here since you expect it to always be set
since callbacks occur on the same thread.

[justinlin, 2012/12/03 21:18:42]

Done. This was previously needed I think when we attached in Open(), so the
callback might not already be set.

+    return 0;
+
+  int frames = callback_->OnMoreData(audio_bus, AudioBuffersState());
+  if (frames < audio_bus->frames())
+    audio_bus->ZeroFramesPartial(frames, audio_bus->frames() - frames);
+
+  return frames > 0 ? volume_ : 0;
+}
+
+bool VirtualAudioOutputStream::CalledOnAudioThread() {
+  return audio_manager_->GetMessageLoop()->BelongsToCurrentThread();
+}
+
+}  // namespace media