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
10namespace content {
11
12namespace {
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().
16int 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
32MediaStreamAudioLevelCalculator::MediaStreamAudioLevelCalculator()
33    : counter_(0),
34      max_amplitude_(0),
35      level_(0) {
36}
37
38MediaStreamAudioLevelCalculator::~MediaStreamAudioLevelCalculator() {
39}
40
41int MediaStreamAudioLevelCalculator::Calculate(
42    const int16* audio_data,
43    int number_of_channels,
44    int number_of_frames,
45    bool force_report_nonzero_energy) {
46  DCHECK(thread_checker_.CalledOnValidThread());
47  // |level_| is updated every 10 callbacks. For the case where callback comes
48  // every 10ms, |level_| will be updated approximately every 100ms.
49  static const int kUpdateFrequency = 10;
50
51  int max = MaxAmplitude(audio_data, number_of_channels * number_of_frames);
52  max_amplitude_ = std::max(max_amplitude_, max);
53
54  if (counter_++ == kUpdateFrequency) {
55    level_ = (max_amplitude_ == 0 ?
56        force_report_nonzero_energy : max_amplitude_);
57
58    // Decay the absolute maximum amplitude by 1/4.
59    max_amplitude_ >>= 2;
60
61    // Reset the counter.
62    counter_ = 0;
63  }
64
65  return level_;
66}
67
68}  // namespace content
69