Improved AGC update scheme for the audio backend in Chrome

media/audio/mac/audio_low_latency_input_mac.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/audio/mac/audio_low_latency_input_mac.h"
 
 #include <CoreServices/CoreServices.h>
 
 #include "base/basictypes.h"
 #include "base/logging.h"
@@ skipping 250 matching lines @@
 
   return true;
 }
 
 void AUAudioInputStream::Start(AudioInputCallback* callback) {
   DCHECK(callback);
   DLOG_IF(ERROR, !audio_unit_) << "Open() has not been called successfully";
   if (started_ || !audio_unit_)
     return;
   sink_ = callback;
+  StartAgc();
   OSStatus result = AudioOutputUnitStart(audio_unit_);
   if (result == noErr) {
     started_ = true;
   }
   OSSTATUS_DLOG_IF(ERROR, result != noErr, result)
       << "Failed to start acquiring data";
 }
 
 void AUAudioInputStream::Stop() {
   if (!started_)
     return;
+  StopAgc();
   OSStatus result = AudioOutputUnitStop(audio_unit_);
   if (result == noErr) {
     started_ = false;
   }
   OSSTATUS_DLOG_IF(ERROR, result != noErr, result)
       << "Failed to stop acquiring data";
 }
 
 void AUAudioInputStream::Close() {
   // It is valid to call Close() before calling open or Start().
@@ skipping 184 matching lines @@
                               audio_input->audio_buffer_list(),
                               time_stamp);
 }
 
 OSStatus AUAudioInputStream::Provide(UInt32 number_of_frames,
                                      AudioBufferList* io_data,
                                      const AudioTimeStamp* time_stamp) {
   // Update the capture latency.
   double capture_latency_frames = GetCaptureLatency(time_stamp);
 
-  // Update the AGC volume level once every second. Note that, |volume| is
-  // also updated each time SetVolume() is called through IPC by the
-  // render-side AGC.
+  // The AGC volume level is updated once every second on a separate thread.
+  // Note that, |volume| is also updated each time SetVolume() is called
+  // through IPC by the render-side AGC.
   double normalized_volume = 0.0;
-  QueryAgcVolume(&normalized_volume);
+  GetAgcVolume(&normalized_volume);
 
   AudioBuffer& buffer = io_data->mBuffers[0];
   uint8* audio_data = reinterpret_cast<uint8*>(buffer.mData);
   uint32 capture_delay_bytes = static_cast<uint32>
       ((capture_latency_frames + 0.5) * format_.mBytesPerFrame);
   DCHECK(audio_data);
   if (!audio_data)
     return kAudioUnitErr_InvalidElement;
 
   // Accumulate captured audio in FIFO until we can match the output size
@@ skipping 149 matching lines @@
     kAudioDevicePropertyScopeInput,
     static_cast<UInt32>(channel)
   };
   OSStatus result = AudioObjectIsPropertySettable(input_device_id_,
                                                   &property_address,
                                                   &is_settable);
   return (result == noErr) ? is_settable : false;
 }
 
 }  // namespace media