| // 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/audio/audio_power_monitor.h" |
| |
| #include <algorithm> |
| #include <cmath> |
| |
| #include "base/float_util.h" |
| #include "base/logging.h" |
| #include "base/time/time.h" |
| #include "media/base/audio_bus.h" |
| |
| namespace media { |
| |
| AudioPowerMonitor::AudioPowerMonitor( |
| int sample_rate, const base::TimeDelta& time_constant) |
| : sample_weight_( |
| 1.0f - expf(-1.0f / (sample_rate * time_constant.InSecondsF()))) { |
| Reset(); |
| } |
| |
| AudioPowerMonitor::~AudioPowerMonitor() { |
| } |
| |
| void AudioPowerMonitor::Reset() { |
| power_reading_ = average_power_ = 0.0f; |
| clipped_reading_ = has_clipped_ = 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 |
| // over the audio samples in |buffer|. |
| // |
| // TODO(miu): Implement optimized SSE/NEON to more efficiently compute the |
| // results (in media/base/vector_math) in soon-upcoming change. |
| float sum_power = 0.0f; |
| for (int i = 0; i < num_channels; ++i) { |
| float average_power_this_channel = average_power_; |
| bool clipped = false; |
| const float* p = buffer.channel(i); |
| const float* const end_of_samples = p + num_frames; |
| for (; p < end_of_samples; ++p) { |
| const float sample = *p; |
| const float sample_squared = sample * sample; |
| clipped |= (sample_squared > 1.0f); |
| average_power_this_channel += |
| (sample_squared - average_power_this_channel) * sample_weight_; |
| } |
| // If data in audio buffer is garbage, ignore its effect on the result. |
| if (base::IsNaN(average_power_this_channel)) { |
| average_power_this_channel = average_power_; |
| clipped = false; |
| } |
| sum_power += average_power_this_channel; |
| has_clipped_ |= clipped; |
| } |
| |
| // Update accumulated results, with clamping for sanity. |
| average_power_ = std::max(0.0f, std::min(1.0f, sum_power / num_channels)); |
| |
| // 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 |