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// Copyright 2014 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 "third_party/blink/renderer/platform/mediastream/media_stream_audio_level_calculator.h"
#include <cmath>
#include <limits>
#include "base/check.h"
#include "base/stl_util.h"
#include "media/base/audio_bus.h"
namespace blink {
namespace {
// Calculates the maximum absolute amplitude of the audio data.
float MaxAmplitude(const float* audio_data, int length) {
float max = 0.0f;
for (int i = 0; i < length; ++i) {
const float absolute = fabsf(audio_data[i]);
if (absolute > max)
max = absolute;
}
DCHECK(std::isfinite(max));
return max;
}
} // namespace
MediaStreamAudioLevelCalculator::Level::Level() : level_(0.0f) {}
MediaStreamAudioLevelCalculator::Level::~Level() {}
float MediaStreamAudioLevelCalculator::Level::GetCurrent() const {
base::AutoLock auto_lock(lock_);
return level_;
}
void MediaStreamAudioLevelCalculator::Level::Set(float level) {
base::AutoLock auto_lock(lock_);
level_ = level;
}
MediaStreamAudioLevelCalculator::MediaStreamAudioLevelCalculator()
: counter_(0), max_amplitude_(0.0f), level_(new Level()) {}
MediaStreamAudioLevelCalculator::~MediaStreamAudioLevelCalculator() {
level_->Set(0.0f);
}
void MediaStreamAudioLevelCalculator::Calculate(
const media::AudioBus& audio_bus,
bool assume_nonzero_energy) {
// |level_| is updated every 10 callbacks. For the case where callback comes
// every 10ms, |level_| will be updated approximately every 100ms.
static const int kUpdateFrequency = 10;
float max =
assume_nonzero_energy ? 1.0f / std::numeric_limits<int16_t>::max() : 0.0f;
for (int i = 0; i < audio_bus.channels(); ++i) {
const float max_this_channel =
MaxAmplitude(audio_bus.channel(i), audio_bus.frames());
if (max_this_channel > max)
max = max_this_channel;
}
max_amplitude_ = std::max(max_amplitude_, max);
if (counter_++ == kUpdateFrequency) {
// Clip the exposed signal level to make sure it is in the range [0.0,1.0].
level_->Set(std::min(1.0f, max_amplitude_));
// Decay the absolute maximum amplitude by 1/4.
max_amplitude_ /= 4.0f;
// Reset the counter.
counter_ = 0;
}
}
} // namespace blink
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