Quelle test_HEAAC_extradata.html Sprache: HTML

products/Sources/formale Sprachen/C/Firefox/dom/media/mediasource/test/test_HEAAC_extradata.html

<!DOCTYPE HTML>
<html>
<head>
  <title>HE-AAC decoding test</title>
  <script src="/tests/SimpleTest/SimpleTest.js"></script>
  <script type="text/javascript" src="mediasource.js"></script>
  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
</head>
<body>
<pre id="test">
<script class="testbody" type="text/javascript">

SimpleTest.waitForExplicitFinish();

const SOURCE_FILE = "whitenoise-he-aac-5s.mp4";

// This test checks when decoding HE-AAC using MediaSource or HTTP playback, the
// audio is decoded correctly (in particular with the SBR part). This means
// that the extradata describing the encoded AAC stream have been communicated
// correctly to the audio decoder. For this, we check that there is energy
// above 10kHz using the Web Audio API when playing white noise, which has
// maximum energy accross the audible spectrum.

// Return the index corresponding for a particular frequency in an array
// containing frequency data from a FFT.
function binIndexForFrequency(frequency, fftSize, sampleRate) {
  return (1 + Math.round((frequency * fftSize) / sampleRate));
}

async function checkHighFrequencyContent(element) {
  const ac = new AudioContext();
  await ac.resume();
  const mediaElementSource = ac.createMediaElementSource(element);
  const analyser = new AnalyserNode(ac);

  // Undo the volume scaling applied globally during test. This is fine because
  // the audio isn't routed to an actual audio output device in this test, it's
  // just analyzed with the Web Audio API.
  const gain = new GainNode(ac);
  const testVolumeScaling =
    parseFloat(SpecialPowers.getCharPref("media.volume_scale"));
  gain.gain.value = 1 / parseFloat(testVolumeScaling);
  mediaElementSource.connect(gain).connect(analyser)

  const spectrum = new Float32Array(analyser.frequencyBinCount);
  const indexFor15kHz =
    binIndexForFrequency(15000, analyser.fftSize, ac.sampleRate);
  // Wait a few hundreds of milliseconds
  while (!element.ended) {
    await once(element, "timeupdate");
    analyser.getFloatFrequencyData(spectrum);
    if (spectrum[indexFor15kHz] > -50) {
      ok(spectrum[indexFor15kHz] > -50,
          `Energy present at 15kHz (bin index: ${indexFor15kHz}) when playing white noise encoded in HE-AAC ${spectrum[indexFor15kHz]}`);
      return;
    }
  }
  ok(false,
      `No energy present at 15kHz (bin index: ${indexFor15kHz}) when playing white noise encoded in HE-AAC (last value ${spectrum[indexFor15kHz]})`);
}

runWithMSE(async (ms, el) => {
  // First check with MSE playback
  el.controls = true;
  await once(ms, "sourceopen");

  const audiosb = ms.addSourceBuffer('audio/mp4; codecs="mp4a.40.5"');
  await fetchAndLoad(audiosb, SOURCE_FILE, [""], "");
  ms.endOfStream();
  el.play();
  once(el, "playing");

  await checkHighFrequencyContent(el);

  // Redo the same test, with HTTP playback
  el.src = SOURCE_FILE;
  el.play();
  once(el, "playing");

  await checkHighFrequencyContent(el);

  SimpleTest.finish();
});

</script>
</pre>
</body>
</html>

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