content/renderer/media/media_stream_audio_level_calculator.cc

   1 // Copyright 2014 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 #include "content/renderer/media/media_stream_audio_level_calculator.h"
   6
   7 #include "base/float_util.h"
   8 #include "base/logging.h"
   9 #include "base/stl_util.h"
  10 #include "media/base/audio_bus.h"
  11
  12 namespace content {
  13
  14 namespace {
  15
  16 // Calculates the maximum absolute amplitude of the audio data.
  17 float MaxAmplitude(const float* audio_data, int length) {
  18   float max = 0.0f;
  19   for (int i = 0; i < length; ++i) {
  20     const float absolute = fabsf(audio_data[i]);
  21     if (absolute > max)
  22       max = absolute;
  23   }
  24   DCHECK(base::IsFinite(max));
  25   return max;
  26 }
  27
  28 }  // namespace
  29
  30 MediaStreamAudioLevelCalculator::MediaStreamAudioLevelCalculator()
  31     : counter_(0),
  32       max_amplitude_(0.0f),
  33       level_(0.0f) {
  34 }
  35
  36 MediaStreamAudioLevelCalculator::~MediaStreamAudioLevelCalculator() {
  37 }
  38
  39 float MediaStreamAudioLevelCalculator::Calculate(
  40     const media::AudioBus& audio_bus) {
  41   DCHECK(thread_checker_.CalledOnValidThread());
  42   // |level_| is updated every 10 callbacks. For the case where callback comes
  43   // every 10ms, |level_| will be updated approximately every 100ms.
  44   static const int kUpdateFrequency = 10;
  45
  46   float max = 0.0f;
  47   for (int i = 0; i < audio_bus.channels(); ++i) {
  48     const float max_this_channel =
  49         MaxAmplitude(audio_bus.channel(i), audio_bus.frames());
  50     if (max_this_channel > max)
  51       max = max_this_channel;
  52   }
  53   max_amplitude_ = std::max(max_amplitude_, max);
  54
  55   if (counter_++ == kUpdateFrequency) {
  56     level_ = max_amplitude_;
  57
  58     // Decay the absolute maximum amplitude by 1/4.
  59     max_amplitude_ /= 4.0f;
  60
  61     // Reset the counter.
  62     counter_ = 0;
  63   }
  64
  65   return level_;
  66 }
  67
  68 }  // namespace content