<!DOCTYPE html>
<html>
<body>
<p>This example uses the HTML DOM to assign an "onplay" event to a video element.</p>
<p>Press play.</p>
<video controls id="myVideo">
<source src="mov_bbb.mp4" type="video/mp4">
<source src="mov_bbb.ogg" 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>
<script>
document.getElementById("myVideo").onplay = function() {myFunction()};
function myFunction() {
alert("The video has started to play.");
}
</script>
</body>
</html>