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
AudioPowerMonitor(int sample_rate,const base::TimeDelta & time_constant)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
~AudioPowerMonitor()25 AudioPowerMonitor::~AudioPowerMonitor() {
26 }
27
Reset()28 void AudioPowerMonitor::Reset() {
29 power_reading_ = average_power_ = 0.0f;
30 clipped_reading_ = has_clipped_ = false;
31 }
32
Scan(const AudioBus & buffer,int num_frames)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
ReadCurrentPowerAndClip()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