media/audio/audio_input_stream_impl.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef MEDIA_AUDIO_AUDIO_INPUT_STREAM_IMPL_H_
   6 #define MEDIA_AUDIO_AUDIO_INPUT_STREAM_IMPL_H_
   7
   8 #include "base/compiler_specific.h"
   9 #include "base/synchronization/lock.h"
  10 #include "base/time.h"
  11 #include "media/audio/audio_io.h"
  12
  13 namespace media {
  14
  15 // AudioInputStreamImpl implements platform-independent parts of the
  16 // AudioInputStream interface. Each platform dependent implementation
  17 // should derive from this class.
  18 // TODO(henrika): we can probably break out more parts from our current
  19 // AudioInputStream implementation and move out to this class.
  20 class MEDIA_EXPORT AudioInputStreamImpl : public AudioInputStream {
  21  public:
  22   AudioInputStreamImpl();
  23   virtual ~AudioInputStreamImpl();
  24
  25   // Sets the automatic gain control (AGC) to on or off. When AGC is enabled,
  26   // the microphone volume is queried periodically and the volume level is
  27   // provided in each AudioInputCallback::OnData() callback and fed to the
  28   // render-side AGC.
  29   virtual void SetAutomaticGainControl(bool enabled) OVERRIDE;
  30
  31   // Gets the current automatic gain control state.
  32   virtual bool GetAutomaticGainControl() OVERRIDE;
  33
  34  protected:
  35   // Stores a new volume level by asking the audio hardware.
  36   // This method only has an effect if AGC is enabled.
  37   void UpdateAgcVolume();
  38
  39   // Gets the latest stored volume level if AGC is enabled and if
  40   // more than one second has passed since the volume was updated the last time.
  41   void QueryAgcVolume(double* normalized_volume);
  42
  43  private:
  44   // Takes a volume sample and stores it in |normalized_volume_|.
  45   void GetNormalizedVolume();
  46
  47   // True when automatic gain control is enabled, false otherwise.
  48   // Guarded by |lock_|.
  49   bool agc_is_enabled_;
  50
  51   // Stores the maximum volume which is used for normalization to a volume
  52   // range of [0.0, 1.0].
  53   double max_volume_;
  54
  55   // Contains last result of internal call to GetVolume(). We save resources
  56   // but not querying the capture volume for each callback. Guarded by |lock_|.
  57   // The range is normalized to [0.0, 1.0].
  58   double normalized_volume_;
  59
  60   // Protects |agc_is_enabled_| and |volume_| .
  61   base::Lock lock_;
  62
  63   // Keeps track of the last time the microphone volume level was queried.
  64   base::Time last_volume_update_time_;
  65
  66   DISALLOW_COPY_AND_ASSIGN(AudioInputStreamImpl);
  67 };
  68
  69 }  // namespace media
  70
  71 #endif  // MEDIA_AUDIO_AUDIO_INPUT_STREAM_IMPL_H_