<!DOCTYPE html>
<html>
<body>
<script>
function myFunction() {
alert("The audio duration has changed");
}
</script>
<video controls ondurationchange="myFunction()">
<source src="https://download.samplelib.com/mp3/sample-3s.mp3" type="video/mp4">
<source src="https://download.samplelib.com/mp3/sample-3s.mp3" type="video/ogg">
Your browser does not support HTML5 video.
</video>
<p>Video courtesy of <a href="https://www.bigbuckbunny.org/" target="_blank">Big Buck Bunny</a>.</p>
</body>
</html>