1 // Copyright 2013 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 "media/audio/audio_power_monitor.h" 6 7 #include <algorithm> 8 #include <cmath> 9 10 #include "base/float_util.h" 11 #include "base/logging.h" 12 #include "base/time/time.h" 13 #include "media/base/audio_bus.h" 14 #include "media/base/vector_math.h" 15 16 namespace media { 17 18 AudioPowerMonitor::AudioPowerMonitor( 19 int sample_rate, const base::TimeDelta& time_constant) 20 : sample_weight_( 21 1.0f - expf(-1.0f / (sample_rate * time_constant.InSecondsF()))) { 22 Reset(); 23 } 24 25 AudioPowerMonitor::~AudioPowerMonitor() { 26 } 27 28 void AudioPowerMonitor::Reset() { 29 power_reading_ = average_power_ = 0.0f; 30 clipped_reading_ = has_clipped_ = false; 31 } 32 33 void AudioPowerMonitor::Scan(const AudioBus& buffer, int num_frames) { 34 DCHECK_LE(num_frames, buffer.frames()); 35 const int num_channels = buffer.channels(); 36 if (num_frames <= 0 || num_channels <= 0) 37 return; 38 39 // Calculate a new average power by applying a first-order low-pass filter 40 // (a.k.a. an exponentially-weighted moving average) over the audio samples in 41 // each channel in |buffer|. 42 float sum_power = 0.0f; 43 for (int i = 0; i < num_channels; ++i) { 44 const std::pair<float, float> ewma_and_max = vector_math::EWMAAndMaxPower( 45 average_power_, buffer.channel(i), num_frames, sample_weight_); 46 // If data in audio buffer is garbage, ignore its effect on the result. 47 if (!base::IsFinite(ewma_and_max.first)) { 48 sum_power += average_power_; 49 } else { 50 sum_power += ewma_and_max.first; 51 has_clipped_ |= (ewma_and_max.second > 1.0f); 52 } 53 } 54 55 // Update accumulated results, with clamping for sanity. 56 average_power_ = std::max(0.0f, std::min(1.0f, sum_power / num_channels)); 57 58 // Push results for reading by other threads, non-blocking. 59 if (reading_lock_.Try()) { 60 power_reading_ = average_power_; 61 if (has_clipped_) { 62 clipped_reading_ = true; 63 has_clipped_ = false; 64 } 65 reading_lock_.Release(); 66 } 67 } 68 69 std::pair<float, bool> AudioPowerMonitor::ReadCurrentPowerAndClip() { 70 base::AutoLock for_reading(reading_lock_); 71 72 // Convert power level to dBFS units, and pin it down to zero if it is 73 // insignificantly small. 74 const float kInsignificantPower = 1.0e-10f; // -100 dBFS 75 const float power_dbfs = power_reading_ < kInsignificantPower ? zero_power() : 76 10.0f * log10f(power_reading_); 77 78 const bool clipped = clipped_reading_; 79 clipped_reading_ = false; 80 81 return std::make_pair(power_dbfs, clipped); 82 } 83 84 } // namespace media 85
