<html class="reftest-wait">
<head>
<script>
async function boom() {
  const audio = document.createElement("audio");
  audio.preload = "metadata";
  audio.src = "sound.ogg";
  await new Promise(r => audio.onloadedmetadata = r);
  const s = audio.mozCaptureStream();
  const recorder = new MediaRecorder(
      new MediaStream(s.getTracks()),
      { audioBitsPerSecond: 3994678619 }
    );
  recorder.start();
  document.documentElement.removeAttribute("class");
}
</script>
</head>
<body onload="boom()">
</body>
</html>
