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AudibilityMonitor.h (3287B)

      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 "AudioBlock.h"
     13 #include "AudioSampleFormat.h"
     14 #include "MediaData.h"
     15 #include "WebAudioUtils.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(Span<const float* const> 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(ConvertAudioSample<float>(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_