<!DOCTYPE html>
<html>
<body>
<script>
function setPlaySpeed() {
document.getElementById("myvideo").playbackRate = 0.3;
}
function myFunction() {
alert("onratechange attribute fired - The playing speed of the video was changed");
}
</script>
<p>Click the button to trigger the "ratechange" event.</p>
<video id="myvideo" autoplay controls onratechange="myFunction()">
<source src="mov_bbb.mp4" type="video/mp4">
<source src="mov_bbb.ogg" type="video/ogg">
Your browser does not support HTML5 video.
</video>
<br>
<button onclick="setPlaySpeed()" type="button">Set video to be play in slow motion</button>
<p>Video courtesy of <a href="https://www.bigbuckbunny.org/" target="_blank">Big Buck Bunny</a>.</p>
</body>
</html>