Adds Analog Gain Control (AGC) to the WebRTC client.

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"
 #include "base/mac/mac_logging.h"
 #include "media/audio/audio_util.h"
 #include "media/audio/mac/audio_manager_mac.h"
 
+static const int kMinIntervalBetweenVolumeUpdatesMs = 1000;
+
 static std::ostream& operator<<(std::ostream& os,
                                 const AudioStreamBasicDescription& format) {
   os << "sample rate       : " << format.mSampleRate << std::endl
      << "format ID         : " << format.mFormatID << std::endl
      << "format flags      : " << format.mFormatFlags << std::endl
      << "bytes per packet  : " << format.mBytesPerPacket << std::endl
      << "frames per packet : " << format.mFramesPerPacket << std::endl
      << "bytes per frame   : " << format.mBytesPerFrame << std::endl
      << "channels per frame: " << format.mChannelsPerFrame << std::endl
      << "bits per channel  : " << format.mBitsPerChannel;
@@ skipping 257 matching lines @@
     // If the volume is settable, the  valid volume range is [0.0, 1.0].
     if (IsVolumeSettableOnChannel(i))
       return 1.0;
   }
 
   // Volume control is not available for the audio stream.
   return 0.0;
 }
 
 void AUAudioInputStream::SetVolume(double volume) {
-  DCHECK(volume <= 1.0 && volume >= 0.0);
+  DVLOG(1) << "SetVolume(volume=" << volume << ")";
+  DCHECK_GE(volume, 0.0);
+  DCHECK_LE(volume, 1.0);
 
   // Verify that we have a valid device.
   if (input_device_id_ == kAudioObjectUnknown) {
     NOTREACHED() << "Device ID is unknown";
     return;
   }
 
   Float32 volume_float32 = static_cast<Float32>(volume);
   AudioObjectPropertyAddress property_address = {
     kAudioDevicePropertyVolumeScalar,
@@ skipping 26 matching lines @@
                                                    NULL,
                                                    sizeof(volume_float32),
                                                    &volume_float32);
       if (result == noErr)
         ++successful_channels;
     }
   }
 
   DLOG_IF(WARNING, successful_channels == 0)
       << "Failed to set volume to " << volume_float32;
+
+  // Update the AGC volume level based on the last setting above. Note that,
+  // the volume-level resolution is not infinite and it is therefore not
+  // possible to assume that the volume provided as input parameter can be
+  // used directly. Instead, a new query to the audio hardware is required.
+  // This method does nothing if AGC is disabled.
+  UpdateAgcVolume();
 }
 
 double AUAudioInputStream::GetVolume() {
   // Verify that we have a valid device.
   if (input_device_id_ == kAudioObjectUnknown){
     NOTREACHED() << "Device ID is unknown";
     return 0.0;
   }
 
   AudioObjectPropertyAddress property_address = {
@@ skipping 77 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.
+  double normalized_volume = 0.0;
+  QueryAgcVolume(&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;
 
-  sink_->OnData(this, audio_data, buffer.mDataByteSize, capture_delay_bytes);
+  // Deliver data packet, delay estimation and volume level to the user.
+  sink_->OnData(this,
+                audio_data,
+                buffer.mDataByteSize,
+                capture_delay_bytes,
+                normalized_volume);
 
   return noErr;
 }
 
 int AUAudioInputStream::HardwareSampleRate() {
   // Determine the default input device's sample-rate.
   AudioDeviceID device_id = kAudioObjectUnknown;
   UInt32 info_size = sizeof(device_id);
 
   AudioObjectPropertyAddress default_input_device_address = {
@@ skipping 120 matching lines @@
   AudioObjectPropertyAddress property_address = {
     kAudioDevicePropertyVolumeScalar,
     kAudioDevicePropertyScopeInput,
     static_cast<UInt32>(channel)
   };
   OSStatus result = AudioObjectIsPropertySettable(input_device_id_,
                                                   &property_address,
                                                   &is_settable);
   return (result == noErr) ? is_settable : false;
 }