Replace AudioSilenceDetector with an AudioPowerMonitor.

media/audio/audio_output_controller.cc

Index: media/audio/audio_output_controller.cc
diff --git a/media/audio/audio_output_controller.cc b/media/audio/audio_output_controller.cc
index f41ed74b65bed526c318cbabc05ec50e2fd5eed6..e508bec6503725589b0acfdd3ed57f5608ee4ff7 100644
--- a/media/audio/audio_output_controller.cc
+++ b/media/audio/audio_output_controller.cc
@@ -11,7 +11,7 @@
 #include "base/threading/platform_thread.h"
 #include "base/time.h"
 #include "build/build_config.h"
-#include "media/audio/audio_silence_detector.h"
+#include "media/audio/audio_power_monitor.h"
 #include "media/audio/audio_util.h"
 #include "media/audio/shared_memory_util.h"
 
@@ -20,16 +20,9 @@ using base::TimeDelta;
 
 namespace media {
 
-// Amount of contiguous time where all audio is silent before considering the
-// stream to have transitioned and EventHandler::OnAudible() should be called.
-static const int kQuestionableSilencePeriodMillis = 50;
-
-// Sample value range below which audio is considered indistinguishably silent.
-//
-// TODO(miu): This value should be specified in dbFS units rather than full
-// scale.  See TODO in audio_silence_detector.h.
-static const float kIndistinguishableSilenceThreshold =
-    1.0f / 4096.0f;  // Note: This is approximately -72 dbFS.
+// Amount of time between calls to EventHandler::OnPowerMeasured() to report
+// current power levels in the audio signal.
+static const float kPowerMeasurementPeriodSeconds = 50.0f / 1000.0f;

[DaleCurtis, 2013/05/16 18:24:45]

Confusing, this doesn't look like it's in seconds? And you use FromMilliseconds
below?

[miu, 2013/05/16 21:44:11]

Doh!  I had already fixed that before requesting the code review.  Just forgot
to upload the latest patch set.  Trololololo...

 
 // Polling-related constants.
 const int AudioOutputController::kPollNumAttempts = 3;
@@ -189,20 +182,20 @@ void AudioOutputController::StartStream() {
   DCHECK(message_loop_->BelongsToCurrentThread());
   state_ = kPlaying;
 
-  silence_detector_.reset(new AudioSilenceDetector(
+  // Start monitoring power levels and send an initial notification that we're
+  // starting in silence.
+  handler_->OnPowerMeasured(AudioPowerMonitor::kZeroPowerDBFS);
+  power_monitor_.reset(new AudioPowerMonitor(
       params_.sample_rate(),
-      TimeDelta::FromMilliseconds(kQuestionableSilencePeriodMillis),
-      kIndistinguishableSilenceThreshold));
+      TimeDelta::FromMilliseconds(kPowerMeasurementPeriodSeconds),
+      MessageLoop::current(),
+      base::Bind(&EventHandler::OnPowerMeasured, base::Unretained(handler_))));
 
   // We start the AudioOutputStream lazily.
   AllowEntryToOnMoreIOData();
   stream_->Start(this);
 
-  // Tell the event handler that we are now playing, and also start the silence
-  // detection notifications.
   handler_->OnPlaying();
-  silence_detector_->Start(
-      base::Bind(&EventHandler::OnAudible, base::Unretained(handler_)));
 }
 
 void AudioOutputController::StopStream() {
@@ -215,8 +208,9 @@ void AudioOutputController::StopStream() {
   } else if (state_ == kPlaying) {
     stream_->Stop();
     DisallowEntryToOnMoreIOData();
-    silence_detector_->Stop(true);
-    silence_detector_.reset();
+    power_monitor_.reset();
+    // Send a final notification that we're ending in silence.
+    handler_->OnPowerMeasured(AudioPowerMonitor::kZeroPowerDBFS);
     state_ = kPaused;
   }
 }
@@ -296,7 +290,7 @@ int AudioOutputController::OnMoreIOData(AudioBus* source,
   sync_reader_->UpdatePendingBytes(
       buffers_state.total_bytes() + frames * params_.GetBytesPerFrame());
 
-  silence_detector_->Scan(dest, frames);
+  power_monitor_->Scan(dest, frames);
 
   AllowEntryToOnMoreIOData();
   return frames;