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

media/audio/win/audio_low_latency_input_win.h

 // 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.
 //
 // Implementation of AudioInputStream for Windows using Windows Core Audio
 // WASAPI for low latency capturing.
 //
 // Overview of operation:
 //
 // - An object of WASAPIAudioInputStream is created by the AudioManager
@@ skipping 47 matching lines @@
 //   require the use of the IAudioEndpointVolume".
 //
 #ifndef MEDIA_AUDIO_WIN_AUDIO_LOW_LATENCY_INPUT_WIN_H_
 #define MEDIA_AUDIO_WIN_AUDIO_LOW_LATENCY_INPUT_WIN_H_
 
 #include <Audioclient.h>
 #include <MMDeviceAPI.h>
 
 #include <string>
 
+#include "base/atomicops.h"
 #include "base/compiler_specific.h"
 #include "base/threading/non_thread_safe.h"
 #include "base/threading/platform_thread.h"
 #include "base/threading/simple_thread.h"
+#include "base/time.h"
 #include "base/win/scoped_co_mem.h"
 #include "base/win/scoped_com_initializer.h"
 #include "base/win/scoped_comptr.h"
 #include "base/win/scoped_handle.h"
 #include "media/audio/audio_io.h"
 #include "media/audio/audio_parameters.h"
 #include "media/base/media_export.h"
 
 class AudioManagerWin;
 
@@ skipping 13 matching lines @@
   virtual ~WASAPIAudioInputStream();
 
   // Implementation of AudioInputStream.
   virtual bool Open() OVERRIDE;
   virtual void Start(AudioInputCallback* callback) OVERRIDE;
   virtual void Stop() OVERRIDE;
   virtual void Close() OVERRIDE;
   virtual double GetMaxVolume() OVERRIDE;
   virtual void SetVolume(double volume) OVERRIDE;
   virtual double GetVolume() OVERRIDE;
+  virtual void SetAutomaticGainControl(bool enabled) OVERRIDE;
+  virtual bool GetAutomaticGainControl() OVERRIDE;
 
   // Retrieves the sample rate used by the audio engine for its internal
   // processing/mixing of shared-mode streams given a specifed device.
   static double HardwareSampleRate(const std::string& device_id);
 
   // Retrieves the number of audio channels used by the audio engine for its
   // internal processing/mixing of shared-mode streams given a specifed device.
   static uint32 HardwareChannelCount(const std::string& device_id);
 
   bool started() const { return started_; }
@@ skipping 54 matching lines @@
   std::string device_id_;
 
   // Conversion factor used in delay-estimation calculations.
   // Converts a raw performance counter value to 100-nanosecond unit.
   double perf_count_to_100ns_units_;
 
   // Conversion factor used in delay-estimation calculations.
   // Converts from milliseconds to audio frames.
   double ms_to_frame_count_;
 
+  // Keeps track of last time a new volume level was fed to the client in an
+  // OnData() callback.
+  base::Time last_volume_update_time_;
+
+  // Contains last result of internal call to GetVolume(). We save resources
+  // but not querying the capture volume for each callback.
+  double volume_;
+
+  // True when Automatic Gain Control is enabled, false otherwise.
+  // This member is modified on the audio thread and read on the internal
+  // WASAPI capture thread in each capture callback.
+  base::subtle::Atomic32 agc_is_enabled_;
+
   // Pointer to the object that will receive the recorded audio samples.
   AudioInputCallback* sink_;
 
   // Windows Multimedia Device (MMDevice) API interfaces.
 
   // An IMMDevice interface which represents an audio endpoint device.
   base::win::ScopedComPtr<IMMDevice> endpoint_device_;
 
   // Windows Audio Session API (WASAP) interfaces.
 
@@ skipping 15 matching lines @@
   // recorded.
   base::win::ScopedHandle audio_samples_ready_event_;
 
   // This event will be signaled when capturing shall stop.
   base::win::ScopedHandle stop_capture_event_;
 
   DISALLOW_COPY_AND_ASSIGN(WASAPIAudioInputStream);
 };
 
 #endif  // MEDIA_AUDIO_WIN_AUDIO_LOW_LATENCY_INPUT_WIN_H_