<!DOCTYPE html>
<html>
<body>
<video id="myVideo" width="320" height="176" controls ondurationchange="myFunction(this)">
<source src="mov_bbb.mp4" type="video/mp4">
<source src="mov_bbb.ogg" type="video/ogg">
Your browser does not support HTML5 video.
</video>
<script>
function myFunction(x) {
alert("The duration of this video is : " + x.duration + " seconds");
}
</script>
<p>This example demonstrates how to use the "ondurationchange" attribute on a VIDEO element.</p>
<p><strong>Note:</strong> When the video is loaded, the "ondurationchange" event will occur, it changes from "NaN" to the actual duration of the video.</p>
<p>Video courtesy of <a href="https://www.bigbuckbunny.org/" target="_blank">Big Buck Bunny</a>.</p>
</body>
</html>