Browser-wide audio mirroring for TabCapture API

media/audio/virtual_audio_output_stream.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 "media/audio/virtual_audio_output_stream.h"
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/logging.h"
+#include "base/message_loop.h"
+#include "media/audio/audio_manager_base.h"
+
+namespace media {
+
+// static
+AudioOutputStream* VirtualAudioOutputStream::MakeStream(
+    AudioManagerBase* manager, const AudioParameters& params) {
+  return new VirtualAudioOutputStream(manager, params);
+}
+
+VirtualAudioOutputStream::VirtualAudioOutputStream(
+    AudioManagerBase* manager, const AudioParameters& params)
+    : audio_manager_(manager),
+      params_(params),
+      callback_(NULL),
+      input_bytes_per_second_(params.GetBytesPerSecond()),
+      io_ratio_(0) {
+}
+
+VirtualAudioOutputStream::~VirtualAudioOutputStream() {
+  DCHECK(!callback_);
+}
+
+bool VirtualAudioOutputStream::Open() {
+  DCHECK(audio_manager_->GetMessageLoop()->BelongsToCurrentThread());
+  return true;
+}
+
+void VirtualAudioOutputStream::Start(AudioSourceCallback* callback)  {
+  DCHECK(audio_manager_->GetMessageLoop()->BelongsToCurrentThread());
+  callback_ = callback;
+}
+
+void VirtualAudioOutputStream::Stop() {
+  DCHECK(audio_manager_->GetMessageLoop()->BelongsToCurrentThread());
+  callback_ = NULL;
+}
+
+void VirtualAudioOutputStream::Close() {
+  DCHECK(!callback_);
+  DCHECK(audio_manager_->GetMessageLoop()->BelongsToCurrentThread());
+  audio_manager_->ReleaseOutputStream(this);
+}
+
+void VirtualAudioOutputStream::SetVolume(double volume) {}
+
+void VirtualAudioOutputStream::GetVolume(double* volume) {
+  *volume = 0;
+}
+
+double VirtualAudioOutputStream::ProvideInput(
+    AudioBus* audio_bus, base::TimeDelta buffer_delay) {
+  if (callback_ == NULL)
+    return 0;
+
+  audio_bus->Zero();
+  int frames = callback_->OnMoreData(audio_bus, AudioBuffersState());
+
+  return frames > 0 ? 1 : 0;
+}
+
+}  // namespace media