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..856419e627ddee1bec4a41a071e71fcb086b8e3b 100644
--- a/content/renderer/media/renderer_webaudiodevice_impl.cc
+++ b/content/renderer/media/renderer_webaudiodevice_impl.cc
@@ -6,9 +6,13 @@
 
 #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/media_switches.h"
 #include "third_party/WebKit/public/web/WebLocalFrame.h"
 #include "third_party/WebKit/public/web/WebView.h"
@@ -20,24 +24,34 @@ using blink::WebView;
 
 namespace content {
 
+static const int kSilenceInSecondsToEnterIdleMode = 30;
+
 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),
+      first_buffer_after_silence_(media::AudioBus::Create(params_)),
+      is_first_buffer_after_silence_(false),
+      start_null_audio_sink_callback_(
+          base::Bind(&media::NullAudioSink::Play, null_audio_sink_)) {
   DCHECK(client_callback_);
+  null_audio_sink_->Initialize(params_, this);
 }
 
 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 +74,16 @@ 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;

[DaleCurtis, 2015/06/23 16:38:14]

Move this below the Stop() since Render() may be in progress up until this
point.

[qinmin, 2015/06/23 18:15:57]

Done.

+  null_audio_sink_->Stop();
+  is_first_buffer_after_silence_ = false;
+  start_null_audio_sink_callback_.Cancel();
+  start_null_audio_sink_callback_.Reset(

[DaleCurtis, 2015/06/23 16:38:14]

Just call Reset() during ::start() and only call Cancel() here (you can remove
the constructor entry then).

[qinmin, 2015/06/23 18:15:57]

Done.

+      base::Bind(&media::NullAudioSink::Play, null_audio_sink_));
 }
 
 double RendererWebAudioDeviceImpl::sampleRate() {
@@ -73,6 +93,14 @@ double RendererWebAudioDeviceImpl::sampleRate() {
 int RendererWebAudioDeviceImpl::Render(media::AudioBus* dest,
                                        int audio_delay_milliseconds) {
   if (client_callback_) {

[DaleCurtis, 2015/06/23 16:38:14]

Looks like this can never be null, can you remove the conditional? Otherwise the
zero check seems like it could pick up uninitialized data.

[qinmin, 2015/06/23 18:15:57]

Done.

+#if defined(OS_ANDROID)
+    if (is_first_buffer_after_silence_) {
+      DCHECK(!is_using_null_audio_sink_);
+      first_buffer_after_silence_->CopyTo(dest);
+      is_first_buffer_after_silence_ = false;
+      return dest->frames();
+    }
+#endif
     // Wrap the output pointers using WebVector.
     WebVector<float*> web_audio_dest_data(
         static_cast<size_t>(dest->channels()));
@@ -87,6 +115,38 @@ 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;
+      is_first_buffer_after_silence_ = true;
+      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_
+        > base::TimeDelta::FromSeconds(kSilenceInSecondsToEnterIdleMode)) {
+      output_device_->Pause();
+      is_using_null_audio_sink_ = true;
+      // If Stop() is called right after the task is posted, need to cancel
+      // this task.
+      task_runner_->PostDelayedTask(
+          FROM_HERE,
+          start_null_audio_sink_callback_.callback(),
+          params_.GetBufferDuration());
+    }
+  }
+#endif
   return dest->frames();
 }