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 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,

[DaleCurtis, 2012/11/28 23:43:18]

This is weird. ~AudioConverter is not virtual either, which it needs to be if
you want to do this.  I'd prefer you just keep an AudioConverter instance inside
LoopbackAudioConverter. Chromium style looks down upon multiple inheritance like
this.

[justinlin, 2012/11/29 10:08:33]

Done.

+      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

[DaleCurtis, 2012/11/28 23:43:18]

operators go on the previous line, this is also going to truncate in weird ways
since MillisecondsPerSecond << params.sample_rate(). One of these shoudl be
casted to float/double.

[miu, 2012/11/29 01:57:40]

Agree with Dale.  Milliseconds is too-coarse a time unit (since the data type is
not a float).  Rather than using:

  int buffer_duration_ms_;

Consider using:

  base::TimeDelta buffer_duration_;

TimeDelta's resolution is in microseconds, which should be good for this use
case.  In fact, I recommend you try to use base/time.h classes as much as
possible since they provide a good interface for writing clean code that does
time calculations.

[justinlin, 2012/11/29 10:08:33]

Well you do the multiplication first, so it shouldn't need to truncate. Unless,
the result isn't always an integer? I was under the impression that buffers are
sized to be some integer duration.

[justinlin, 2012/11/29 10:08:33]

Done.

+                          / 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::ReadAudio, base::Unretained(this)));
+  next_read_time_ = base::Time::Now();
+  audio_manager_->GetMessageLoop()->PostTask(
+      FROM_HERE, on_more_data_cb_.callback());
+}
+
+void VirtualAudioInputStream::Stop() {

[DaleCurtis, 2012/11/28 23:43:18]

DCHECK(belongs to current thread).

[justinlin, 2012/11/29 10:08:33]

Done.

+  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));

[DaleCurtis, 2012/11/28 23:43:18]

This is unnecessary since every VirtualAudioOutputStream knows it's params_ just
force them to be passed in for RemoveOutputStream.

[justinlin, 2012/11/29 10:08:33]

Done. Right, don't need it anymore after moving the attach/detach to the VAOS.

+
+  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_)));

[DaleCurtis, 2012/11/28 23:43:18]

I'd choose a different name for one of these |params| and |params_| values, it's
just asking for a typo like this.

[justinlin, 2012/11/29 10:08:33]

Done.

+    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) {
+  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::ReadAudio() {
+  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);

[DaleCurtis, 2012/11/28 23:43:18]

Can't do mixed indentation like this, either all aligned, or all 4 space
indented.

[justinlin, 2012/11/29 10:08:33]

Done.

+
+  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.
+  if (delay < base::TimeDelta())

[DaleCurtis, 2012/11/28 23:43:18]

This is risky and not worth the effort IMHO. On slower machines or machines
under load you may always be behind and thus spin the CPU. Regular data
intervals are more important than worrying about falling behind in this case.
I'd revert this to the original approach.

[miu, 2012/11/29 01:57:40]

I think that's actually what Justin was attempting to do here.  The word
"catchup" in the comment might be misleading.  Unless I'm mistaken, the
intention for this code is: Attempt to time things to regular intervals, and if
we detect we've missed an interval, skip it and just go on to the next.

That said, the code doesn't quite work.  For one, next_read_time_ is not reset
forward to account for the intentional skip-ahead.

Justin: Please see what I did in ScheduleNextFrameCapture() in
web_contents_video_capture_device.cc.

[justinlin, 2012/11/29 10:08:33]

Done.

[justinlin, 2012/11/29 10:08:33]

Yea, I probably misunderstood your last comment. I *was* trying to do what it
looked like here: try to "catchup" by scheduling the next callback sooner if we
start falling behind. Dale is right that this would not bode well on slower
machines. 

I'm not sure if we can read ahead or what the repercussions of doing that are
(i.e. might cause video to playback faster due to av sync). We can revisit in a
future CL.

+    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