Browser-wide audio mirroring for TabCapture API

media/audio/virtual_audio_input_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_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 this
+// audio conversion from input to output params to be used as an input stream to
+// other AudioConverters.
+class LoopbackAudioConverter
+    : public AudioConverter,
+      public AudioConverter::InputCallback {
+ public:
+  LoopbackAudioConverter(const AudioParameters& input_params,
+                         const AudioParameters& output_params);
+  virtual ~LoopbackAudioConverter() {}
+
+ private:
+  virtual double ProvideInput(
+      AudioBus* audio_bus, base::TimeDelta buffer_delay) OVERRIDE;
+
+  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),
+      callback_delay_(static_cast<float>(params.frames_per_buffer())

[miu, 2012/11/26 21:14:55]

Consider changing this to:

  callback_delay_(base::TimeDelta::FromMicroseconds(
    params.frames_per_buffer() * base::Time::kMicrosecondsPerSecond /
        params.sample_rate())),

(Note that there's no need for floating-point math here if you do the multiply
before the divide.)

And then fix code on line 121 that uses callback_delay_.

Also, because of the "scheduling code" change, you may want to rename this to
callback_period_.

[justinlin, 2012/11/27 22:26:12]

Done. Thanks

+                      / params.sample_rate()
+                      * base::Time::kMillisecondsPerSecond),
+      buffer_(new uint8[params.GetBytesPerBuffer()]),
+      params_(params),
+      audio_bus_(AudioBus::Create(params_)),
+      mixer_(params_, params_, false) {
+}
+
+VirtualAudioInputStream::~VirtualAudioInputStream() {
+  for (AudioConvertersMap::iterator it = converters_.begin();
+       it != converters_.end(); ++it) {
+    delete it->second;
+  }
+}
+
+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)));
+  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));
+
+  LoopbackAudioConverter*& converter = converters_[params];
+  if (!converter) {
+    converter = new LoopbackAudioConverter(params, params_);
+    // Add to main mixer if we just added a new AudioTransform.
+    mixer_.AddInput(converter);
+  }
+  converter->AddInput(stream);
+}
+
+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);
+  // TODO(justinlin): Do we need to delete the AudioConverter and remove it from
+  // the mixer when there's no more input streams?
+
+  output_params_.erase(stream);
+}
+
+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);
+
+  // TODO(justinlin): DO_NOT_SUBMIT, try out Yuri's idea for scheduling next

[miu, 2012/11/26 21:14:55]

I think you meant to include the timestamp-based scheduling calculations in this
CL.  ;-)

[justinlin, 2012/11/27 22:26:12]

Done.

+  // time.
+
+  MessageLoop::current()->PostDelayedTask(

[no longer working on chromium, 2012/11/27 12:36:15]

you should cache the message loop for the polling here, otherwise AudioManager
will swap its message loop to NULL in the shutdown, and it will crash here. 

[justinlin, 2012/11/27 22:26:12]

Hmm.. is it safe to schedule into that message loop then? Or, should we just
check if it's NULL and do nothing if that's the case?

+      FROM_HERE, on_more_data_cb_.callback(),
+      base::TimeDelta::FromMilliseconds(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;
+}
+
+LoopbackAudioConverter::LoopbackAudioConverter(
+    const AudioParameters& input_params, const AudioParameters& output_params)
+    : AudioConverter(input_params, output_params, false) {
+}
+
+double LoopbackAudioConverter::ProvideInput(
+    AudioBus* audio_bus, base::TimeDelta buffer_delay) {
+  Convert(audio_bus);
+  return 1.0;
+}
+
+}  // namespace media