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
16namespace media {
17
18AudioPowerMonitor::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
25AudioPowerMonitor::~AudioPowerMonitor() {
26}
27
28void AudioPowerMonitor::Reset() {
29  power_reading_ = average_power_ = 0.0f;
30  clipped_reading_ = has_clipped_ = false;
31}
32
33void 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
69std::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