Browser-wide audio mirroring for TabCapture API

media/audio/virtual_audio_input_stream.cc

Index: media/audio/virtual_audio_input_stream.cc
diff --git a/media/audio/virtual_audio_input_stream.cc b/media/audio/virtual_audio_input_stream.cc
new file mode 100644
index 0000000000000000000000000000000000000000..4f2f9bd04fb84a4619766597777c75665b5641c6
--- /dev/null
+++ b/media/audio/virtual_audio_input_stream.cc
@@ -0,0 +1,173 @@
+// 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_input_stream.h"
+
+#include <algorithm>
+#include <utility>
+
+#include "base/bind.h"
+#include "base/message_loop.h"
+#include "media/audio/virtual_audio_output_stream.h"
+
+namespace media {
+
+// LoopbackAudioConverter works similar to AudioConverter and converts input
+// streams to different audio parameters. Then, the LoopbackAudioConverter can
+// be used as an input to another AudioConverter. This allows us to
+// use converted audio from AudioOutputStreams as input to an AudioConverter.
+// For example, this allows converting multiple streams into a common format and
+// using the converted audio as input to another AudioConverter (i.e. a mixer).
+class LoopbackAudioConverter : public AudioConverter::InputCallback {
+ public:
+  LoopbackAudioConverter(const AudioParameters& input_params,
+                         const AudioParameters& output_params)
+      : audio_converter_(input_params, output_params, false) {}
+
+  virtual ~LoopbackAudioConverter() {}
+
+  void AddInput(AudioConverter::InputCallback* input) {
+    audio_converter_.AddInput(input);
+  }
+
+  void RemoveInput(AudioConverter::InputCallback* input) {
+    audio_converter_.RemoveInput(input);
+  }
+
+ private:
+  virtual double ProvideInput(AudioBus* audio_bus,
+                              base::TimeDelta buffer_delay) OVERRIDE {
+    audio_converter_.Convert(audio_bus);
+    return 1.0;
+  }
+
+  AudioConverter audio_converter_;
+
+  DISALLOW_COPY_AND_ASSIGN(LoopbackAudioConverter);
+};
+
+VirtualAudioInputStream* VirtualAudioInputStream::MakeStream(
+    AudioManagerBase* manager, const AudioParameters& params,
+    base::MessageLoopProxy* message_loop) {
+  return new VirtualAudioInputStream(manager, params, message_loop);
+}
+
+VirtualAudioInputStream::VirtualAudioInputStream(
+    AudioManagerBase* manager, const AudioParameters& params,
+    base::MessageLoopProxy* message_loop)
+    : audio_manager_(manager),
+      message_loop_(message_loop),
+      callback_(NULL),
+      buffer_duration_ms_(base::TimeDelta::FromMilliseconds(
+          params.frames_per_buffer() * base::Time::kMillisecondsPerSecond /
+          static_cast<float>(params.sample_rate()))),
+      buffer_(new uint8[params.GetBytesPerBuffer()]),
+      params_(params),
+      audio_bus_(AudioBus::Create(params_)),
+      mixer_(params_, params_, false),
+      num_attached_outputs_streams_(0) {
+}
+
+VirtualAudioInputStream::~VirtualAudioInputStream() {
+  for (AudioConvertersMap::iterator it = converters_.begin();
+       it != converters_.end(); ++it)
+    delete it->second;
+
+  DCHECK_EQ(0, num_attached_outputs_streams_);
+}
+
+bool VirtualAudioInputStream::Open() {
+  memset(buffer_.get(), 0, params_.GetBytesPerBuffer());
+  return true;
+}
+
+void VirtualAudioInputStream::Start(AudioInputCallback* callback) {
+  DCHECK(message_loop_->BelongsToCurrentThread());
+  callback_ = callback;
+  on_more_data_cb_.Reset(base::Bind(&VirtualAudioInputStream::ReadAudio,
+                                    base::Unretained(this)));
+  audio_manager_->GetMessageLoop()->PostTask(FROM_HERE,
+                                             on_more_data_cb_.callback());
+}
+
+void VirtualAudioInputStream::Stop() {
+  DCHECK(message_loop_->BelongsToCurrentThread());
+  on_more_data_cb_.Cancel();
+}
+
+void VirtualAudioInputStream::AddOutputStream(
+    VirtualAudioOutputStream* stream, const AudioParameters& output_params) {
+  DCHECK(message_loop_->BelongsToCurrentThread());
+
+  AudioConvertersMap::iterator converter = converters_.find(output_params);
+  if (converter == converters_.end()) {
+    std::pair<AudioConvertersMap::iterator, bool> result = converters_.insert(
+        std::make_pair(output_params,
+                       new LoopbackAudioConverter(output_params, params_)));
+    converter = result.first;
+
+    // Add to main mixer if we just added a new AudioTransform.
+    mixer_.AddInput(converter->second);
+  }
+  converter->second->AddInput(stream);
+  ++num_attached_outputs_streams_;
+}
+
+void VirtualAudioInputStream::RemoveOutputStream(
+    VirtualAudioOutputStream* stream, const AudioParameters& output_params) {
+  DCHECK(message_loop_->BelongsToCurrentThread());
+
+  DCHECK(converters_.find(output_params) != converters_.end());
+  converters_[output_params]->RemoveInput(stream);
+
+  --num_attached_outputs_streams_;
+}
+
+void VirtualAudioInputStream::ReadAudio() {
+  DCHECK(message_loop_->BelongsToCurrentThread());
+  DCHECK(callback_);
+
+  mixer_.Convert(audio_bus_.get());
+  audio_bus_->ToInterleaved(params_.frames_per_buffer(),
+                            params_.bits_per_sample() / 8,
+                            buffer_.get());
+
+  callback_->OnData(this,
+                    buffer_.get(),
+                    params_.GetBytesPerBuffer(),
+                    params_.GetBytesPerBuffer(),
+                    1.0);
+
+  message_loop_->PostDelayedTask(FROM_HERE,
+                                 on_more_data_cb_.callback(),
+                                 buffer_duration_ms_);
+}
+
+void VirtualAudioInputStream::Close() {
+  DCHECK(message_loop_->BelongsToCurrentThread());
+  if (callback_) {
+    DCHECK(on_more_data_cb_.IsCancelled());
+    callback_->OnClose(this);
+    callback_ = NULL;
+  }
+  audio_manager_->ReleaseInputStream(this);
+}
+
+double VirtualAudioInputStream::GetMaxVolume() {
+  return 1.0;
+}
+
+void VirtualAudioInputStream::SetVolume(double volume) {}
+
+double VirtualAudioInputStream::GetVolume() {
+  return 1.0;
+}
+
+void VirtualAudioInputStream::SetAutomaticGainControl(bool enabled) {}
+
+bool VirtualAudioInputStream::GetAutomaticGainControl() {
+  return false;
+}
+
+}  // namespace media