getUserMedia-framerate-decimation.https.html

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This WPT test may be referenced by the following Test IDs:
- /mediacapture-streams/getUserMedia-framerate-decimation.https.html - WPT Dashboard Interop Dashboard

<!doctype html>

<title>getUserMedia crop-and-scale framerate decimation. Assumes Mozilla's fake camera with 640x480@30fps capability.</title>

<meta name="timeout" content="long">

<script src=/resources/testharness.js></script>

<script src=/resources/testharnessreport.js></script>

<script src=/resources/testdriver.js></script>

<script src=/resources/testdriver-vendor.js></script>

<script>

"use strict"

promise_test(async t => {

  const stream = await navigator.mediaDevices.getUserMedia({

    video: {width: 640, height: 480, frameRate: 24, resizeMode: "crop-and-scale"}

});

  const [track] = stream.getTracks();

  t.add_cleanup(async () => track.stop());

  const video = document.createElement("video");

  document.body.appendChild(video);

  t.add_cleanup(async () => document.body.removeChild(video));

  video.style = "width:320px;height:240px;";

  video.srcObject = new MediaStream([track]);

  await video.play();

  // Wait for the compositor to report painted frames before measuring.

  while (video.mozPaintedFrames == 0) {

    await new Promise(r => t.step_timeout(r, 50));

  const frames1 = video.mozPaintedFrames;

  const t1 = performance.now();

  await new Promise(r => t.step_timeout(r, 1000));

  const frames2 = video.mozPaintedFrames;

  const elapsed = (performance.now() - t1) / 1000;

  const avgFps = (frames2 - frames1) / elapsed;

  // 30fps source decimated to 24fps target: expect ~24fps, not ~15fps

  // (15fps is what floor-to-divisor produces for non-divisor targets).

  assert_between_exclusive(avgFps, 19, 29, "Framerate should be ~24fps");

}, "crop-and-scale framerate decimation achieves target framerate on average");

</script>