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..4b1bb6d4234a64d25f3b189a7e0201adfeb2bf06
--- /dev/null
+++ b/media/audio/virtual_audio_input_stream.cc
@@ -0,0 +1,167 @@
+// 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 "base/bind.h"
+#include "base/message_loop.h"
+#include "media/audio/virtual_audio_output_stream.h"
+
+namespace media {
+
+// AudioConverter that can also be used an as InputCallback. This allows us to
+// use converted audio from an AudioOutputStream 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,
+      public AudioConverter::InputCallback {
+ public:
+  LoopbackAudioConverter(const AudioParameters& input_params,
+                         const AudioParameters& output_params)
+      : AudioConverter(input_params, output_params, false) {}
+
+  virtual ~LoopbackAudioConverter() {}
+
+ private:
+  virtual double ProvideInput(AudioBus* audio_bus,
+                              base::TimeDelta buffer_delay) OVERRIDE {
+    Convert(audio_bus);
+    return 1.0;
+  }
+
+  DISALLOW_COPY_AND_ASSIGN(LoopbackAudioConverter);
+};
+
+VirtualAudioInputStream* VirtualAudioInputStream::MakeStream(
+    AudioManagerBase* manager, const AudioParameters& params) {
+  return new VirtualAudioInputStream(manager, params);
+}
+
+VirtualAudioInputStream::VirtualAudioInputStream(AudioManagerBase* manager,
+                                                 const AudioParameters& params)
+    : audio_manager_(manager),
+      callback_(NULL),
+      buffer_duration_ms_(params.frames_per_buffer()
+                          * base::Time::kMillisecondsPerSecond
+                          / 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(audio_manager_->GetMessageLoop()->BelongsToCurrentThread());
+  callback_ = callback;
+  on_more_data_cb_.Reset(base::Bind(
+      &VirtualAudioInputStream::DoCallback, base::Unretained(this)));
+  next_read_time_ = base::Time::Now();
+  audio_manager_->GetMessageLoop()->PostTask(
+      FROM_HERE, on_more_data_cb_.callback());
+}
+
+void VirtualAudioInputStream::Stop() {
+  on_more_data_cb_.Cancel();
+}
+
+void VirtualAudioInputStream::AddOutputStream(
+    VirtualAudioOutputStream* stream, const AudioParameters& params) {
+  DCHECK(audio_manager_->GetMessageLoop()->BelongsToCurrentThread());
+  output_params_.insert(std::make_pair(stream, params));
+
+  AudioConvertersMap::iterator converter = converters_.find(params);
+  if (converter == converters_.end()) {
+    std::pair<AudioConvertersMap::iterator, bool> result = converters_.insert(
+        std::make_pair<AudioParameters, LoopbackAudioConverter*>(
+            params, new LoopbackAudioConverter(params, params_)));
+    converter = result.first;
+    // Add to main mixer if we just added a new AudioTransform.

[Alpha Left Google, 2012/11/28 21:26:51]

nit: empty line before comments.

+    mixer_.AddInput(converter->second);
+  }
+  converter->second->AddInput(stream);
+  ++num_attached_outputs_streams_;
+}
+
+void VirtualAudioInputStream::RemoveOutputStream(
+    VirtualAudioOutputStream* stream) {
+  DCHECK(audio_manager_->GetMessageLoop()->BelongsToCurrentThread());
+  DCHECK(output_params_.find(stream) != output_params_.end());
+  const AudioParameters& params = output_params_[stream];
+
+  DCHECK(converters_.find(params) != converters_.end());
+  converters_[params]->RemoveInput(stream);
+
+  output_params_.erase(stream);
+  --num_attached_outputs_streams_;
+}
+
+void VirtualAudioInputStream::DoCallback() {
+  DCHECK(audio_manager_->GetMessageLoop()->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);
+
+  next_read_time_ += base::TimeDelta::FromMilliseconds(buffer_duration_ms_);
+  base::TimeDelta delay = next_read_time_ - base::Time::Now();
+  // Try to catchup if we fall behind.

[Alpha Left Google, 2012/11/28 21:26:51]

nit: empty line before comments.

+  if (delay < base::TimeDelta())
+    delay = base::TimeDelta();
+
+  MessageLoop* message_loop = MessageLoop::current();
+  if (message_loop) {
+    message_loop->PostDelayedTask(
+        FROM_HERE, on_more_data_cb_.callback(), delay);
+  }
+}
+
+void VirtualAudioInputStream::Close() {
+  DCHECK(audio_manager_->GetMessageLoop()->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