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- // 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 <algorithm>
- #include <cmath>
- #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<float, float> 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<float, bool> 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
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