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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef DOM_MEDIA_AUDIBILITYMONITOR_H_
+#define DOM_MEDIA_AUDIBILITYMONITOR_H_
+
+#include <cstdint>
+
+#include "AudioSampleFormat.h"
+#include "WebAudioUtils.h"
+#include "AudioBlock.h"
+#include "MediaData.h"
+
+namespace mozilla {
+
+class AudibilityMonitor {
+ public:
+ // ≈ 20 * log10(pow(2, 12)), noise floor of 12bit audio
+ const float AUDIBILITY_THRESHOLD =
+ dom::WebAudioUtils::ConvertDecibelsToLinear(-72.);
+
+ AudibilityMonitor(uint32_t aSamplerate, float aSilenceDurationSeconds)
+ : mSamplerate(aSamplerate),
+ mSilenceDurationSeconds(aSilenceDurationSeconds),
+ mSilentFramesInARow(0),
+ mEverAudible(false) {}
+
+ void Process(const AudioData* aData) {
+ ProcessInterleaved(aData->Data(), aData->mChannels);
+ }
+
+ void Process(const AudioBlock& aData) {
+ if (aData.IsNull() || aData.IsMuted()) {
+ mSilentFramesInARow += aData.GetDuration();
+ return;
+ }
+ ProcessPlanar(aData.ChannelData<float>(), aData.GetDuration());
+ }
+
+ void ProcessPlanar(Span<const float* const> aPlanar, TrackTime aFrames) {
+ uint32_t lastFrameAudibleAcrossChannels = 0;
+ for (uint32_t channel = 0; channel < aPlanar.Length(); channel++) {
+ uint32_t lastSampleAudible = 0;
+ for (uint32_t frame = 0; frame < aFrames; frame++) {
+ if (std::fabs(aPlanar[channel][frame]) > AUDIBILITY_THRESHOLD) {
+ mEverAudible = true;
+ mSilentFramesInARow = 0;
+ lastSampleAudible = frame;
+ }
+ }
+ lastFrameAudibleAcrossChannels =
+ std::max(lastFrameAudibleAcrossChannels, lastSampleAudible);
+ }
+ mSilentFramesInARow += aFrames - lastFrameAudibleAcrossChannels - 1;
+ }
+
+ void ProcessInterleaved(const Span<AudioDataValue>& aInterleaved,
+ size_t aChannels) {
+ MOZ_ASSERT(aInterleaved.Length() % aChannels == 0);
+ uint32_t frameCount = aInterleaved.Length() / aChannels;
+ AudioDataValue* samples = aInterleaved.Elements();
+
+ uint32_t readIndex = 0;
+ for (uint32_t i = 0; i < frameCount; i++) {
+ bool atLeastOneAudible = false;
+ for (uint32_t j = 0; j < aChannels; j++) {
+ if (std::fabs(AudioSampleToFloat(samples[readIndex++])) >
+ AUDIBILITY_THRESHOLD) {
+ atLeastOneAudible = true;
+ }
+ }
+ if (atLeastOneAudible) {
+ mSilentFramesInARow = 0;
+ mEverAudible = true;
+ } else {
+ mSilentFramesInARow++;
+ }
+ }
+ }
+
+ // A stream is considered audible if there was audible content in the last
+ // `mSilenceDurationSeconds` seconds, or it has never been audible for now.
+ bool RecentlyAudible() {
+ return mEverAudible && (static_cast<float>(mSilentFramesInARow) /
+ mSamplerate) < mSilenceDurationSeconds;
+ }
+
+ private:
+ const uint32_t mSamplerate;
+ const float mSilenceDurationSeconds;
+ uint64_t mSilentFramesInARow;
+ bool mEverAudible;
+};
+
+}; // namespace mozilla
+
+#endif // DOM_MEDIA_AUDIBILITYMONITOR_H_