media/audio/audio_power_monitor.cc

   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/logging.h"
  11 #include "base/time/time.h"
  12 #include "media/base/audio_bus.h"
  13 #include "media/base/vector_math.h"
  14
  15 namespace media {
  16
  17 AudioPowerMonitor::AudioPowerMonitor(
  18     int sample_rate, const base::TimeDelta& time_constant)
  19     : sample_weight_(
  20           1.0f - expf(-1.0f / (sample_rate * time_constant.InSecondsF()))) {
  21   Reset();
  22 }
  23
  24 AudioPowerMonitor::~AudioPowerMonitor() {
  25 }
  26
  27 void AudioPowerMonitor::Reset() {
  28   // These are only read/written by Scan(), but Scan() should not be running
  29   // when Reset() is called.
  30   average_power_ = 0.0f;
  31   has_clipped_ = false;
  32
  33   // These are the copies read by ReadCurrentPowerAndClip().  The lock here is
  34   // not necessary, as racey writes/reads are acceptable, but this prevents
  35   // quality-enhancement tools like TSAN from complaining.
  36   base::AutoLock for_reset(reading_lock_);
  37   power_reading_ = 0.0f;
  38   clipped_reading_ = false;
  39 }
  40
  41 void AudioPowerMonitor::Scan(const AudioBus& buffer, int num_frames) {
  42   DCHECK_LE(num_frames, buffer.frames());
  43   const int num_channels = buffer.channels();
  44   if (num_frames <= 0 || num_channels <= 0)
  45     return;
  46
  47   // Calculate a new average power by applying a first-order low-pass filter
  48   // (a.k.a. an exponentially-weighted moving average) over the audio samples in
  49   // each channel in |buffer|.
  50   float sum_power = 0.0f;
  51   for (int i = 0; i < num_channels; ++i) {
  52     const std::pair<float, float> ewma_and_max = vector_math::EWMAAndMaxPower(
  53         average_power_, buffer.channel(i), num_frames, sample_weight_);
  54     // If data in audio buffer is garbage, ignore its effect on the result.
  55     if (!std::isfinite(ewma_and_max.first)) {
  56       sum_power += average_power_;
  57     } else {
  58       sum_power += ewma_and_max.first;
  59       has_clipped_ |= (ewma_and_max.second > 1.0f);
  60     }
  61   }
  62
  63   // Update accumulated results, with clamping for sanity.
  64   average_power_ = std::max(0.0f, std::min(1.0f, sum_power / num_channels));
  65
  66   // Push results for reading by other threads, non-blocking.
  67   if (reading_lock_.Try()) {
  68     power_reading_ = average_power_;
  69     if (has_clipped_) {
  70       clipped_reading_ = true;
  71       has_clipped_ = false;
  72     }
  73     reading_lock_.Release();
  74   }
  75 }
  76
  77 std::pair<float, bool> AudioPowerMonitor::ReadCurrentPowerAndClip() {
  78   base::AutoLock for_reading(reading_lock_);
  79
  80   // Convert power level to dBFS units, and pin it down to zero if it is
  81   // insignificantly small.
  82   const float kInsignificantPower = 1.0e-10f;  // -100 dBFS
  83   const float power_dbfs = power_reading_ < kInsignificantPower ? zero_power() :
  84       10.0f * log10f(power_reading_);
  85
  86   const bool clipped = clipped_reading_;
  87   clipped_reading_ = false;
  88
  89   return std::make_pair(power_dbfs, clipped);
  90 }
  91
  92 }  // namespace media