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