Adds volume level measurements to the AudioInputController for low-latency clients

media/audio/audio_input_controller.cc

Index: media/audio/audio_input_controller.cc
diff --git a/media/audio/audio_input_controller.cc b/media/audio/audio_input_controller.cc
index 3bdec149bfc3c3605bdb7234edf522199fedb783..40afb90474f8cd3e6270301d5cdf045e1ea6dca7 100644
--- a/media/audio/audio_input_controller.cc
+++ b/media/audio/audio_input_controller.cc
@@ -6,10 +6,13 @@
 
 #include "base/bind.h"
 #include "base/threading/thread_restrictions.h"
+#include "base/time/time.h"
 #include "media/base/limits.h"
 #include "media/base/scoped_histogram_timer.h"
 #include "media/base/user_input_monitor.h"
 
+using base::TimeDelta;
+
 namespace {
 const int kMaxInputChannels = 3;
 
@@ -25,6 +28,13 @@ const int kTimerResetIntervalSeconds = 1;
 // Mac devices and the initial timer interval has therefore been increased
 // from 1 second to 5 seconds.
 const int kTimerInitialIntervalSeconds = 5;
+
+// Time constant for AudioPowerMonitor.  See AudioPowerMonitor ctor comments for
+// semantics.  This value was arbitrarily chosen, but seems to work well.
+const int kPowerMeasurementTimeConstantMillis = 10;
+
+// Time between two successive measurements of audio power levels.
+const int kPowerMonitorLogIntervalMilliSeconds = 500;
 }
 
 namespace media {
@@ -173,6 +183,13 @@ void AudioInputController::DoCreate(AudioManager* audio_manager,
                                     const std::string& device_id) {
   DCHECK(task_runner_->BelongsToCurrentThread());
   SCOPED_UMA_HISTOGRAM_TIMER("Media.AudioInputController.CreateTime");
+
+  // Create the audio (power) level meter given the provided audio parameters.
+  audio_level_.reset(new media::AudioPowerMonitor(params.sample_rate(),
+      TimeDelta::FromMilliseconds(kPowerMeasurementTimeConstantMillis)));
+  audio_bus_ = AudioBus::Create(params);
+  audio_params_ = params;
+
   // TODO(miu): See TODO at top of file.  Until that's resolved, assume all
   // platform audio input requires the |no_data_timer_| be used to auto-detect
   // errors.  In reality, probably only Windows needs to be treated as
@@ -266,6 +283,9 @@ void AudioInputController::DoClose() {
   // Delete the timer on the same thread that created it.
   no_data_timer_.reset();
 
+  if (audio_level_)

[no longer working on chromium, 2014/05/19 15:15:48]

skip if

[henrika (OOO until Aug 14), 2014/05/19 15:25:46]

It can be NULL.

+    audio_level_->Reset();
+
   DoStopCloseAndClearStream();
   SetDataIsActive(false);
 
@@ -377,6 +397,35 @@ void AudioInputController::OnData(AudioInputStream* stream,
   if (SharedMemoryAndSyncSocketMode()) {
     sync_writer_->Write(data, size, volume, key_pressed);
     sync_writer_->UpdateRecordedBytes(hardware_delay_bytes);
+
+    if (!audio_level_)

[no longer working on chromium, 2014/05/19 15:15:48]

can audio_level be NULL?

[henrika (OOO until Aug 14), 2014/05/19 15:25:46]

Yes, using new ctor. I can modify and create when needed instead.

+      return;
+
+    // Perform periodic audio (power) level measurements.
+    if ((base::TimeTicks::Now() - last_audio_level_log_time_).InMilliseconds() >
+        kPowerMonitorLogIntervalMilliSeconds) {
+      last_audio_level_log_time_ = base::TimeTicks::Now();
+      audio_bus_->FromInterleaved(
+          data, audio_bus_->frames(), audio_params_.bits_per_sample() / 8);
+      audio_level_->Scan(*audio_bus_, audio_bus_->frames());
+      std::pair<float, bool> result = audio_level_->ReadCurrentPowerAndClip();
+
+      // Get the audible level in the range [0.0,1.0], where 0.0 means
+      // the audio signal is silent and 1.0 means it is at maximum volume.
+      float level_dbfs = result.first;
+      float level = 0;
+      static const float kSilenceThresholdDBFS = -72.24719896f;
+      if (level_dbfs < kSilenceThresholdDBFS)
+        level = 0.0f;
+      else if (level_dbfs > 0.0f)
+        level = 1.0f;
+      else
+        level = 1.0f - level_dbfs / kSilenceThresholdDBFS;
+      DVLOG(1) << "audio_level: " << level;
+
+      audio_level_->Reset();
+    }
+
     return;
   }