audio_power_monitor.h revision c2db58bd994c04d98e4ee2cd7565b71548655fe3
1ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch// Copyright 2013 The Chromium Authors. All rights reserved. 2ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch// Use of this source code is governed by a BSD-style license that can be 3ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch// found in the LICENSE file. 4ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch 5ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch#ifndef MEDIA_AUDIO_AUDIO_POWER_MONITOR_H_ 6ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch#define MEDIA_AUDIO_AUDIO_POWER_MONITOR_H_ 7ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch 8ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch#include <limits> 9c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch#include <utility> 10ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch 11ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch#include "base/callback.h" 12c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch#include "base/synchronization/lock.h" 13ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch#include "media/base/media_export.h" 14ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch 15ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch// An audio signal power monitor. It is periodically provided an AudioBus by 16ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch// the native audio thread, and the audio samples in each channel are analyzed 17ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch// to determine the average power of the signal over a time period. Here 18ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch// "average power" is a running average calculated by using a first-order 19ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch// low-pass filter over the square of the samples scanned. Whenever reporting 20ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch// the power level, this running average is converted to dBFS (decibels relative 21ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch// to full-scale) units. 22ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch// 23ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch// Note that extreme care has been taken to make the AudioPowerMonitor::Scan() 24ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch// method safe to be called on the native audio thread. The code acquires no 25ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch// locks, nor engages in any operation that could result in an 26ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch// undetermined/unbounded amount of run-time. 27ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch 28ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdochnamespace base { 29ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdochclass TimeDelta; 30ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch} 31ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch 32ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdochnamespace media { 33ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch 34ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdochclass AudioBus; 35ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch 36ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdochclass MEDIA_EXPORT AudioPowerMonitor { 37ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch public: 38ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch // |sample_rate| is the audio signal sample rate (Hz). |time_constant| 39ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch // characterizes how samples are averaged over time to determine the power 40ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch // level; and is the amount of time it takes a zero power level to increase to 41c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch // ~63.2% of maximum given a step input signal. 42c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch AudioPowerMonitor(int sample_rate, const base::TimeDelta& time_constant); 43ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch 44ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch ~AudioPowerMonitor(); 45ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch 46c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch // Reset power monitor to initial state (zero power level). This should not 47c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch // be called while another thread is scanning. 48c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch void Reset(); 49c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch 50ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch // Scan more |frames| of audio data from |buffer|. It is safe to call this 51ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch // from a real-time priority thread. 52ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch void Scan(const AudioBus& buffer, int frames); 53ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch 54c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch // Returns the current power level in dBFS and clip status. Clip status is 55c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch // true whenever any *one* sample scanned exceeded maximum amplitude since 56c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch // this method's last invocation. It is safe to call this method from any 57c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch // thread. 58c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch std::pair<float, bool> ReadCurrentPowerAndClip(); 59c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch 60ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch // dBFS value corresponding to zero power in the audio signal. 61ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch static float zero_power() { return -std::numeric_limits<float>::infinity(); } 62ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch 63ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch // dBFS value corresponding to maximum power in the audio signal. 64ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch static float max_power() { return 0.0f; } 65ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch 66ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch private: 67ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch // The weight applied when averaging-in each sample. Computed from the 68ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch // |sample_rate| and |time_constant|. 69ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch const float sample_weight_; 70ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch 71c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch // Accumulated results over one or more calls to Scan(). These should only be 72c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch // touched by the thread invoking Scan(). 73ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch float average_power_; 74c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch bool has_clipped_; 75ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch 76c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch // Copies of power and clip status, used to deliver results synchronously 77c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch // across threads. 78c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch base::Lock reading_lock_; 79c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch float power_reading_; 80c2db58bd994c04d98e4ee2cd7565b71548655fe3Ben Murdoch bool clipped_reading_; 81ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch 82ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch DISALLOW_COPY_AND_ASSIGN(AudioPowerMonitor); 83ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch}; 84ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch 85ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch} // namespace media 86ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch 87ca12bfac764ba476d6cd062bf1dde12cc64c3f40Ben Murdoch#endif // MEDIA_AUDIO_AUDIO_POWER_MONITOR_H_ 88