// Copyright 2013 The Chromium Authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. #include "media/base/audio_power_monitor.h" #include #include #include "base/check_op.h" #include "base/cxx17_backports.h" #include "base/time/time.h" #include "media/base/audio_bus.h" #include "media/base/vector_math.h" namespace media { AudioPowerMonitor::AudioPowerMonitor(int sample_rate, base::TimeDelta time_constant) : sample_weight_(1.0f - expf(-1.0f / (sample_rate * time_constant.InSecondsF()))) { Reset(); } AudioPowerMonitor::~AudioPowerMonitor() = default; void AudioPowerMonitor::Reset() { // These are only read/written by Scan(), but Scan() should not be running // when Reset() is called. average_power_ = 0.0f; has_clipped_ = false; // These are the copies read by ReadCurrentPowerAndClip(). The lock here is // not necessary, as racey writes/reads are acceptable, but this prevents // quality-enhancement tools like TSAN from complaining. base::AutoLock for_reset(reading_lock_); power_reading_ = 0.0f; clipped_reading_ = false; } void AudioPowerMonitor::Scan(const AudioBus& buffer, int num_frames) { DCHECK_LE(num_frames, buffer.frames()); const int num_channels = buffer.channels(); if (num_frames <= 0 || num_channels <= 0) return; // Calculate a new average power by applying a first-order low-pass filter // (a.k.a. an exponentially-weighted moving average) over the audio samples in // each channel in |buffer|. float sum_power = 0.0f; for (int i = 0; i < num_channels; ++i) { const std::pair ewma_and_max = vector_math::EWMAAndMaxPower( average_power_, buffer.channel(i), num_frames, sample_weight_); // If data in audio buffer is garbage, ignore its effect on the result. if (!std::isfinite(ewma_and_max.first)) { sum_power += average_power_; } else { sum_power += ewma_and_max.first; has_clipped_ |= (ewma_and_max.second > 1.0f); } } // Update accumulated results, with clamping for sanity. average_power_ = base::clamp(sum_power / num_channels, 0.0f, 1.0f); // Push results for reading by other threads, non-blocking. if (reading_lock_.Try()) { power_reading_ = average_power_; if (has_clipped_) { clipped_reading_ = true; has_clipped_ = false; } reading_lock_.Release(); } } std::pair AudioPowerMonitor::ReadCurrentPowerAndClip() { base::AutoLock for_reading(reading_lock_); // Convert power level to dBFS units, and pin it down to zero if it is // insignificantly small. const float kInsignificantPower = 1.0e-10f; // -100 dBFS const float power_dbfs = power_reading_ < kInsignificantPower ? zero_power() : 10.0f * log10f(power_reading_); const bool clipped = clipped_reading_; clipped_reading_ = false; return std::make_pair(power_dbfs, clipped); } } // namespace media