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chromium/third_party/blink/web_tests/external/wpt/webaudio/the-audio-api/the-pannernode-interface/test-pannernode-automation.html 

<!doctype html>
<meta charset=utf-8>
<title></title>
<script src=/resources/testharness.js></script>
<script src=/resources/testharnessreport.js></script>
<script>

// This value is purposefuly not aligned on a 128-block boundary so that we test
// that the PannerNode position audioparam is a-rate.
const POSITION_CHANGE_FRAME = 1111;

promise_test(function(t) {
  var ac = new OfflineAudioContext(2, 2048, 44100);
  var panner = ac.createPanner();
  panner.positionX.value = -1;
  panner.positionY.value = -1;
  panner.positionZ.value = 1;
  panner.positionX.setValueAtTime(1, POSITION_CHANGE_FRAME/ac.sampleRate);
  var osc = ac.createOscillator();
  osc.connect(panner);
  panner.connect(ac.destination);
  osc.start()
  return ac.startRendering().then(function(buffer) {
    var left = buffer.getChannelData(0);
    var right = buffer.getChannelData(1);
    for (var i = 0; i < 2048; ++i) {
      if (i < POSITION_CHANGE_FRAME) {
        assert_true(Math.abs(left[i]) >= Math.abs(right[i]), "index " + i + " should be on the left");
      } else {
        assert_true(Math.abs(left[i]) < Math.abs(right[i]), "index " + i + " should be on the right");
      }
    }
  });
}, "PannerNode AudioParam automation works properly");

</script>