dom/media/AudibilityMonitor.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef DOM_MEDIA_AUDIBILITYMONITOR_H_
   8 #define DOM_MEDIA_AUDIBILITYMONITOR_H_
   9
  10 #include <cstdint>
  11
  12 #include "AudioSampleFormat.h"
  13 #include "WebAudioUtils.h"
  14 #include "AudioBlock.h"
  15 #include "MediaData.h"
  16
  17 namespace mozilla {
  18
  19 class AudibilityMonitor {
  20  public:
  21   // ≈ 20 * log10(pow(2, 12)), noise floor of 12bit audio
  22   const float AUDIBILITY_THRESHOLD =
  23       dom::WebAudioUtils::ConvertDecibelsToLinear(-72.);
  24
  25   AudibilityMonitor(uint32_t aSamplerate, float aSilenceDurationSeconds)
  26       : mSamplerate(aSamplerate),
  27         mSilenceDurationSeconds(aSilenceDurationSeconds),
  28         mSilentFramesInARow(0),
  29         mEverAudible(false) {}
  30
  31   void Process(const AudioData* aData) {
  32     ProcessInterleaved(aData->Data(), aData->mChannels);
  33   }
  34
  35   void Process(const AudioBlock& aData) {
  36     if (aData.IsNull() || aData.IsMuted()) {
  37       mSilentFramesInARow += aData.GetDuration();
  38       return;
  39     }
  40     ProcessPlanar(aData.ChannelData<float>(), aData.GetDuration());
  41   }
  42
  43   void ProcessPlanar(const nsTArray<const float*>& aPlanar, TrackTime aFrames) {
  44     uint32_t lastFrameAudibleAcrossChannels = 0;
  45     for (uint32_t channel = 0; channel < aPlanar.Length(); channel++) {
  46       uint32_t lastSampleAudible = 0;
  47       for (uint32_t frame = 0; frame < aFrames; frame++) {
  48         if (std::fabs(aPlanar[channel][frame]) > AUDIBILITY_THRESHOLD) {
  49           mEverAudible = true;
  50           mSilentFramesInARow = 0;
  51           lastSampleAudible = frame;
  52         }
  53       }
  54       lastFrameAudibleAcrossChannels =
  55           std::max(lastFrameAudibleAcrossChannels, lastSampleAudible);
  56     }
  57     mSilentFramesInARow += aFrames - lastFrameAudibleAcrossChannels - 1;
  58   }
  59
  60   void ProcessInterleaved(const Span<AudioDataValue>& aInterleaved,
  61                           size_t aChannels) {
  62     MOZ_ASSERT(aInterleaved.Length() % aChannels == 0);
  63     uint32_t frameCount = aInterleaved.Length() / aChannels;
  64     AudioDataValue* samples = aInterleaved.Elements();
  65
  66     uint32_t readIndex = 0;
  67     for (uint32_t i = 0; i < frameCount; i++) {
  68       bool atLeastOneAudible = false;
  69       for (uint32_t j = 0; j < aChannels; j++) {
  70         if (std::fabs(AudioSampleToFloat(samples[readIndex++])) >
  71             AUDIBILITY_THRESHOLD) {
  72           atLeastOneAudible = true;
  73         }
  74       }
  75       if (atLeastOneAudible) {
  76         mSilentFramesInARow = 0;
  77         mEverAudible = true;
  78       } else {
  79         mSilentFramesInARow++;
  80       }
  81     }
  82   }
  83
  84   // A stream is considered audible if there was audible content in the last
  85   // `mSilenceDurationSeconds` seconds, or it has never been audible for now.
  86   bool RecentlyAudible() {
  87     return mEverAudible && (static_cast<float>(mSilentFramesInARow) /
  88                             mSamplerate) < mSilenceDurationSeconds;
  89   }
  90
  91  private:
  92   const uint32_t mSamplerate;
  93   const float mSilenceDurationSeconds;
  94   uint64_t mSilentFramesInARow;
  95   bool mEverAudible;
  96 };
  97
  98 };  // namespace mozilla
  99
 100 #endif  // DOM_MEDIA_AUDIBILITYMONITOR_H_