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