Bug 1830206 - Rework AudioSink's ringbuffer size computation. r=alwu, a=RyanVM

Differential Revision: https://phabricator.services.mozilla.com/D178074

dom/media/mediasink/AudioSink.cpp

@@ -53,13 +53,22 @@ AudioSink::AudioSink(AbstractThread* aThread,
       mAudioQueue(aAudioQueue),
       mProcessedQueueThresholdMS(
           StaticPrefs::media_audio_audiosink_threshold_ms()) {
+  // Not much to initialize here if there's no audio.
+  if (!aInfo.IsValid()) {
+    mProcessedSPSCQueue = MakeUnique<SPSCQueue<AudioDataValue>>(0);
+    return;
+  }
   // Twice the limit that trigger a refill.
-  float capacitySeconds = mProcessedQueueThresholdMS / 1000.f * 2;
-  mProcessedSPSCQueue =
-      MakeUnique<SPSCQueue<AudioDataValue>>(static_cast<uint32_t>(
-          capacitySeconds * static_cast<float>(mOutputChannels * mOutputRate)));
+  double capacitySeconds = mProcessedQueueThresholdMS / 1000.f * 2;
+  // Clamp to correct boundaries, and align on the channel count
+  int elementCount = static_cast<int>(
+      std::clamp(capacitySeconds * mOutputChannels * mOutputRate, 0.,
+                 std::numeric_limits<int>::max() - 1.));
+  elementCount -= elementCount % mOutputChannels;
+  mProcessedSPSCQueue = MakeUnique<SPSCQueue<AudioDataValue>>(elementCount);
   SINK_LOG("Ringbuffer has space for %u elements (%lf seconds)",
-           mProcessedSPSCQueue->Capacity(), capacitySeconds);
+           mProcessedSPSCQueue->Capacity(),
+           static_cast<float>(elementCount) / mOutputChannels / mOutputRate);
   // Determine if the data is likely to be audible when the stream will be
   // ready, if possible.
   RefPtr<AudioData> frontPacket = mAudioQueue.PeekFront();