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/logging.h"
   8 #include "base/stl_util.h"
   9
  10 namespace content {
  11
  12 namespace {
  13
  14 // Calculates the maximum absolute amplitude of the audio data.
  15 // Note, the return value can be bigger than std::numeric_limits<int16>::max().
  16 int MaxAmplitude(const int16* audio_data, int length) {
  17   int max = 0, absolute = 0;
  18   for (int i = 0; i < length; ++i) {
  19     absolute = std::abs(audio_data[i]);
  20     if (absolute > max)
  21       max = absolute;
  22   }
  23   // The range of int16 is [-32768, 32767], verify the |max| should not be
  24   // bigger than 32768.
  25   DCHECK(max <= std::abs(std::numeric_limits<int16>::min()));
  26
  27   return max;
  28 }
  29
  30 }  // namespace
  31
  32 MediaStreamAudioLevelCalculator::MediaStreamAudioLevelCalculator()
  33     : counter_(0),
  34       max_amplitude_(0),
  35       level_(0) {
  36 }
  37
  38 MediaStreamAudioLevelCalculator::~MediaStreamAudioLevelCalculator() {
  39 }
  40
  41 int MediaStreamAudioLevelCalculator::Calculate(const int16* audio_data,
  42                                                int number_of_channels,
  43                                                int number_of_frames) {
  44   DCHECK(thread_checker_.CalledOnValidThread());
  45   // |level_| is updated every 10 callbacks. For the case where callback comes
  46   // every 10ms, |level_| will be updated approximately every 100ms.
  47   static const int kUpdateFrequency = 10;
  48
  49   int max = MaxAmplitude(audio_data, number_of_channels * number_of_frames);
  50   max_amplitude_ = std::max(max_amplitude_, max);
  51
  52   if (counter_++ == kUpdateFrequency) {
  53     level_ = max_amplitude_;
  54
  55     // Decay the absolute maximum amplitude by 1/4.
  56     max_amplitude_ >>= 2;
  57
  58     // Reset the counter.
  59     counter_ = 0;
  60   }
  61
  62   return level_;
  63 }
  64
  65 }  // namespace content