1 files changed, 100 insertions, 0 deletions
diff --git a/dom/media/AudibilityMonitor.h b/dom/media/AudibilityMonitor.h
new file mode 100644
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+++ b/dom/media/AudibilityMonitor.h
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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(const nsTArray<const float*>& 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_