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

media/audio/linux/alsa_input.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/linux/alsa_input.h"
 
 #include "base/basictypes.h"
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/message_loop.h"
@@ skipping 181 matching lines @@
         FROM_HERE,
         base::Bind(&AlsaPcmInputStream::ReadAudio, weak_factory_.GetWeakPtr()),
         next_check_time);
     return;
   }
 
   int num_buffers = frames / params_.frames_per_buffer();
   int num_buffers_read = num_buffers;
   uint32 hardware_delay_bytes =
       static_cast<uint32>(GetCurrentDelay() * params_.GetBytesPerFrame());
+  double normalized_volume = 0.0;
+
+  // 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.
+  QueryAgcVolume(&normalized_volume);
+
   while (num_buffers--) {
     int frames_read = wrapper_->PcmReadi(device_handle_, audio_buffer_.get(),
                                          params_.frames_per_buffer());
     if (frames_read == params_.frames_per_buffer()) {
       callback_->OnData(this, audio_buffer_.get(), bytes_per_buffer_,
-                        hardware_delay_bytes);
+                        hardware_delay_bytes, normalized_volume);
     } else {
       LOG(WARNING) << "PcmReadi returning less than expected frames: "
                    << frames_read << " vs. " << params_.frames_per_buffer()
                    << ". Dropping this buffer.";
     }
   }
 
   next_read_time_ += base::TimeDelta::FromMilliseconds(
       buffer_duration_ms_ * num_buffers_read);
   base::TimeDelta delay = next_read_time_ - base::Time::Now();
@@ skipping 78 matching lines @@
   if (!mixer_handle_ || !mixer_element_handle_) {
     DLOG(WARNING) << "SetVolume is not supported for " << device_name_;
     return;
   }
 
   int error = wrapper_->MixerSelemSetCaptureVolumeAll(
       mixer_element_handle_, static_cast<long>(volume));
   if (error < 0) {
     DLOG(WARNING) << "Unable to set volume for " << device_name_;
   }
+
+  // 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 AlsaPcmInputStream::GetVolume() {
   if (!mixer_handle_ || !mixer_element_handle_) {
     DLOG(WARNING) << "GetVolume is not supported for " << device_name_;
     return 0.0;
   }
 
   long current_volume = 0;
   int error = wrapper_->MixerSelemGetCaptureVolume(
       mixer_element_handle_, static_cast<snd_mixer_selem_channel_id_t>(0),
       &current_volume);
   if (error < 0) {
     DLOG(WARNING) << "Unable to get volume for " << device_name_;
     return 0.0;
   }
 
   return static_cast<double>(current_volume);
 }
 
 void AlsaPcmInputStream::HandleError(const char* method, int error) {
   LOG(WARNING) << method << ": " << wrapper_->StrError(error);
   callback_->OnError(this, error);
 }