Add a silent audio sink to consume WebAudio data on silence detection.

content/renderer/media/renderer_webaudiodevice_impl.cc

Index: content/renderer/media/renderer_webaudiodevice_impl.cc
diff --git a/content/renderer/media/renderer_webaudiodevice_impl.cc b/content/renderer/media/renderer_webaudiodevice_impl.cc
index 81817f79818c0bb0b68cdd31197f4d9a03f731ae..a714831201fe9d8fa0b2c783cb3d297dff94ef6f 100644
--- a/content/renderer/media/renderer_webaudiodevice_impl.cc
+++ b/content/renderer/media/renderer_webaudiodevice_impl.cc
@@ -6,9 +6,14 @@
 
 #include "base/command_line.h"
 #include "base/logging.h"
+#include "base/single_thread_task_runner.h"
+#include "base/thread_task_runner_handle.h"
+#include "base/time/time.h"
 #include "content/renderer/media/audio_device_factory.h"
 #include "content/renderer/render_frame_impl.h"
 #include "media/audio/audio_output_device.h"
+#include "media/audio/null_audio_sink.h"
+#include "media/base/audio_timestamp_helper.h"

[DaleCurtis, 2015/06/22 22:49:42]

Remove?

[qinmin, 2015/06/23 00:01:54]

Done.

 #include "media/base/media_switches.h"
 #include "third_party/WebKit/public/web/WebLocalFrame.h"
 #include "third_party/WebKit/public/web/WebView.h"
@@ -20,24 +25,32 @@ using blink::WebView;
 
 namespace content {
 
+static const int kSilenceInSecondsToEnterIdleMode = 30.0;

[DaleCurtis, 2015/06/22 22:49:42]

Remove .0

[qinmin, 2015/06/23 00:01:54]

Done.

+
 RendererWebAudioDeviceImpl::RendererWebAudioDeviceImpl(
     const media::AudioParameters& params,
     WebAudioDevice::RenderCallback* callback,
     int session_id)
     : params_(params),
       client_callback_(callback),
-      session_id_(session_id) {
+      session_id_(session_id),
+      task_runner_(base::ThreadTaskRunnerHandle::Get()),
+      null_audio_sink_(new media::NullAudioSink(task_runner_)),
+      is_using_null_audio_sink_(false),
+      weak_factory_(this) {

[DaleCurtis, 2015/06/22 22:49:42]

Remove.

[qinmin, 2015/06/23 00:01:54]

Done.

   DCHECK(client_callback_);
+  null_audio_sink_->Initialize(params_, this);
+  weak_this_ = weak_factory_.GetWeakPtr();

[DaleCurtis, 2015/06/22 22:49:42]

Remove.

[qinmin, 2015/06/23 00:01:54]

Done.

 }
 
 RendererWebAudioDeviceImpl::~RendererWebAudioDeviceImpl() {
-  DCHECK(!output_device_.get());
+  DCHECK(!output_device_);
 }
 
 void RendererWebAudioDeviceImpl::start() {
   DCHECK(thread_checker_.CalledOnValidThread());
 
-  if (output_device_.get())
+  if (output_device_)
     return;  // Already started.
 
   // Assumption: This method is being invoked within a V8 call stack.  CHECKs
@@ -60,10 +73,13 @@ void RendererWebAudioDeviceImpl::start() {
 void RendererWebAudioDeviceImpl::stop() {
   DCHECK(thread_checker_.CalledOnValidThread());
 
-  if (output_device_.get()) {
+  if (output_device_) {
     output_device_->Stop();
     output_device_ = NULL;
   }
+  is_using_null_audio_sink_ = false;
+  null_audio_sink_->Stop();
+  first_buffer_after_silence_.reset();
 }
 
 double RendererWebAudioDeviceImpl::sampleRate() {
@@ -73,6 +89,14 @@ double RendererWebAudioDeviceImpl::sampleRate() {
 int RendererWebAudioDeviceImpl::Render(media::AudioBus* dest,
                                        int audio_delay_milliseconds) {
   if (client_callback_) {
+#if defined(OS_ANDROID)
+    if (first_buffer_after_silence_) {
+      DCHECK(!is_using_null_audio_sink_);
+      first_buffer_after_silence_->CopyTo(dest);
+      first_buffer_after_silence_.reset();
+      return dest->frames();
+    }
+#endif
     // Wrap the output pointers using WebVector.
     WebVector<float*> web_audio_dest_data(
         static_cast<size_t>(dest->channels()));
@@ -87,6 +111,42 @@ int RendererWebAudioDeviceImpl::Render(media::AudioBus* dest,
                              dest->frames());
   }
 
+#if defined(OS_ANDROID)
+  const bool is_zero = dest->AreFramesZero();
+  if (!is_zero) {
+    first_silence_time_ = base::TimeTicks();
+    if (is_using_null_audio_sink_) {
+      // This is called on the main render thread when audio is detected.
+      output_device_->Play();
+      is_using_null_audio_sink_ = false;
+      first_buffer_after_silence_ = media::AudioBus::Create(params_);

[DaleCurtis, 2015/06/22 22:49:42]

If we ever lower the silence threshold it might be better to only create once
and use a bool for checking.

[qinmin, 2015/06/23 00:01:54]

Done.

+      dest->CopyTo(first_buffer_after_silence_.get());
+      task_runner_->PostTask(
+          FROM_HERE,
+          base::Bind(&media::NullAudioSink::Stop, null_audio_sink_));
+    }
+  } else if (!is_using_null_audio_sink_) {
+    // Called on the audio device thread.
+    const base::TimeTicks now = base::TimeTicks::Now();
+    if (first_silence_time_.is_null())
+      first_silence_time_ = now;
+    if ((now - first_silence_time_).InSecondsF()

[DaleCurtis, 2015/06/22 22:49:42]

Instead of doing this, compare against
base::TimeDelta::FromSeconds(kSilenceInSecondsToEnterIdleMode)

[qinmin, 2015/06/23 00:01:54]

Done.

+        > kSilenceInSecondsToEnterIdleMode) {
+      output_device_->Pause();
+      is_using_null_audio_sink_ = true;
+      // If Stop() is called right after the task is posted,

[DaleCurtis, 2015/06/22 22:49:42]

This isn't true, only the Stop() above is safe, you need to cancel this task if
Stop() is called before it runs. Otherwise the ref will keep the null sink
alive, but be called after Stop() (which may even be after the destruction of
this class), so playback could start post-destruction.

I'd just use a base::CancelableClosure to do this, bind it during construction
and vend cancelable_closure_.callback() here. Then during Stop() just call
cancelable_closure_.Cancel().

[qinmin, 2015/06/23 00:01:54]

That's why I kept the weak_ptr_ here. If StartNullAudioSink() is posted and
Stop() is immediately called, Stop() should set is_using_null_audio_sink_ to
false and stop the null_audio_sink_ from playing. And if
RendererWebAudioDeviceImpl is destructed right after the task is posted, the
weak_ptr will keep StartNullAudioSink() from running.
Anyway, since weak_ptr_ is gone, switch to cancelableClosure. The problem with
cancelableClosure is that it has to be created and canceled on the same thread,
so we have to reconstruct the cancelableClosure right after we cancel it.

+      // StartNullAudioSink() should do nothing.
+      double delay =

[DaleCurtis, 2015/06/22 22:49:42]

Just use params_.GetBufferDuration()

[qinmin, 2015/06/23 00:01:54]

Thanks, didn't notice that method.

+          static_cast<double>(dest->frames() *
+              base::Time::kMicrosecondsPerSecond) / params_.sample_rate();
+      task_runner_->PostDelayedTask(
+          FROM_HERE,
+          base::Bind(&RendererWebAudioDeviceImpl::StartNullAudioSink,

[DaleCurtis, 2015/06/22 22:49:42]

Bind directly to Play() here.

[qinmin, 2015/06/23 00:01:54]

Done.

+                     weak_this_),
+          base::TimeDelta::FromMicroseconds(delay));
+    }
+  }
+#endif
   return dest->frames();
 }
 
@@ -94,4 +154,9 @@ void RendererWebAudioDeviceImpl::OnRenderError() {
   // TODO(crogers): implement error handling.
 }
 
+void RendererWebAudioDeviceImpl::StartNullAudioSink() {

[DaleCurtis, 2015/06/22 22:49:42]

Delete?

[qinmin, 2015/06/23 00:01:54]

Done.

+  if (is_using_null_audio_sink_)
+    null_audio_sink_->Play();
+}
+
 }  // namespace content