Browser-wide audio mirroring for TabCapture API

media/audio/audio_manager_base.cc

Index: media/audio/audio_manager_base.cc
diff --git a/media/audio/audio_manager_base.cc b/media/audio/audio_manager_base.cc
index 7b79613774c2b66ad3031794daf7810f894a1ddf..bcf189efbe9dd5b96fd07e6ae3796f0f737f93f9 100644
--- a/media/audio/audio_manager_base.cc
+++ b/media/audio/audio_manager_base.cc
@@ -14,6 +14,8 @@
 #include "media/audio/audio_util.h"
 #include "media/audio/fake_audio_input_stream.h"
 #include "media/audio/fake_audio_output_stream.h"
+#include "media/audio/virtual_audio_input_stream.h"
+#include "media/audio/virtual_audio_output_stream.h"
 #include "media/base/media_switches.h"
 
 // TODO(dalecurtis): Temporarily disabled while switching pipeline to use float,
@@ -45,7 +47,8 @@ AudioManagerBase::AudioManagerBase()
       max_num_input_streams_(kDefaultMaxInputStreams),
       num_output_streams_(0),
       num_input_streams_(0),
-      audio_thread_(new base::Thread("AudioThread")) {
+      audio_thread_(new base::Thread("AudioThread")),
+      virtual_audio_input_stream_(NULL) {
 #if defined(OS_WIN)
   audio_thread_->init_com_with_mta(true);
 #endif
@@ -100,7 +103,14 @@ AudioOutputStream* AudioManagerBase::MakeAudioOutputStream(
       !HasAudioOutputDevices();
 
   AudioOutputStream* stream = NULL;
-  if (audio_output_disabled) {
+  if (virtual_audio_input_stream_ &&
+      params.format() != AudioParameters::AUDIO_FAKE) {
+    // TODO(justinlin): This seems to sometimes be called twice for 1 video.

[Alpha Left Google, 2012/11/28 01:04:47]

What should this TODO do?

[justinlin, 2012/11/28 14:30:31]

Right, I'll remove the TODO and fix this.

+    // They both attach, but then one of them detaches prematurely, and the
+    // other one doesn't detach which causes a DCHECK fail?
+    stream = VirtualAudioOutputStream::MakeStream(this, params,
+                                                  virtual_audio_input_stream_);
+  } else if (audio_output_disabled) {
     stream = FakeAudioOutputStream::MakeFakeStream(this, params);
   } else if (params.format() == AudioParameters::AUDIO_PCM_LINEAR) {
     stream = MakeLinearOutputStream(params);
@@ -130,7 +140,24 @@ AudioInputStream* AudioManagerBase::MakeAudioInputStream(
   }
 
   AudioInputStream* stream = NULL;
-  if (params.format() == AudioParameters::AUDIO_FAKE) {
+  if (params.format() == AudioParameters::AUDIO_MIRROR_BROWSER) {
+    // TODO(justinlin): Currently, we can only support mirroring audio from 1

[Alpha Left Google, 2012/11/28 01:04:47]

No need to mention tab.

You can just mention the limitation of current implementation.

[justinlin, 2012/11/28 14:30:31]

Done.

+    // tab, so subsequent tab capture requests will just get fake audio.
+    // Maybe we should just return the same stream and ref-count, so that we
+    // only actually destroy the stream when there's no mirroring?
+    if (!virtual_audio_input_stream_) {
+      virtual_audio_input_stream_ =
+          VirtualAudioInputStream::MakeStream(this, params);
+      stream = virtual_audio_input_stream_;
+      message_loop_->PostTask(FROM_HERE, base::Bind(

[Alpha Left Google, 2012/11/28 01:04:47]

What would this task do?

[justinlin, 2012/11/28 14:30:31]

NotifyAllOutputChangeListeners needs to be called on the AudioThread. I looks
like this is usually called on the audio thread too normally, but that's not the
case in unit tests, so we need to post.

+          &AudioManagerBase::NotifyAllOutputDeviceChangeListeners,
+          base::Unretained(this)));
+    } else {
+      // TODO(justinlin): Maybe we can return NULL if this doesn't cause the

[Alpha Left Google, 2012/11/28 01:04:47]

This code doesn't need a TODO isn't it?

[justinlin, 2012/11/28 14:30:31]

Done.

+      // media request to fail?
+      stream = FakeAudioInputStream::MakeFakeStream(this, params);
+    }
+  } else if (params.format() == AudioParameters::AUDIO_FAKE) {
     stream = FakeAudioInputStream::MakeFakeStream(this, params);
   } else if (params.format() == AudioParameters::AUDIO_PCM_LINEAR) {
     stream = MakeLinearInputStream(params, device_id);
@@ -233,6 +260,7 @@ void AudioManagerBase::GetAudioInputDeviceNames(
 }
 
 void AudioManagerBase::ReleaseOutputStream(AudioOutputStream* stream) {
+  DCHECK(message_loop_->BelongsToCurrentThread());
   DCHECK(stream);
   // TODO(xians) : Have a clearer destruction path for the AudioOutputStream.
   // For example, pass the ownership to AudioManager so it can delete the
@@ -242,8 +270,16 @@ void AudioManagerBase::ReleaseOutputStream(AudioOutputStream* stream) {
 }
 
 void AudioManagerBase::ReleaseInputStream(AudioInputStream* stream) {
+  DCHECK(message_loop_->BelongsToCurrentThread());
   DCHECK(stream);
   // TODO(xians) : Have a clearer destruction path for the AudioInputStream.
+
+  if (virtual_audio_input_stream_ == stream) {
+    virtual_audio_input_stream_->Stop();
+    virtual_audio_input_stream_ = NULL;
+    NotifyAllOutputDeviceChangeListeners();

[Alpha Left Google, 2012/11/28 01:04:47]

What should the output streams do? Write a comment to explain.

[justinlin, 2012/11/28 14:30:31]

Done.

+  }
+
   num_input_streams_--;
   delete stream;
 }