chromium/third_party/blink/web_tests/media/track/track-cue-rendering-horizontal.html

<!DOCTYPE html>
<title>Test, rendering horizontal line-positioned cues.</title>
<video>
    <track src="captions-webvtt/captions-snap-to-lines-set.vtt" kind="captions" default>
</video>
<script>
var video = document.querySelector("video");
video.src = "../content/test.ogv";

testRunner.waitUntilDone();
video.onseeked = function() {
    testRunner.notifyDone();
}

video.currentTime = 0.25;
</script>