<!DOCTYPE html>
<html lang="en-US">
<head>
<style>
video{
width:100%;
height:330px
}
</style>
</head>
<body>
<video controls>
<source src="/hawk.mp4" type="video/WMV">
</video>
<script>
var x = document.getElementsByTagName("source")[0];
function myFunction(){
alert("This video is in mp4 format");
}
x.addEventListener("error", myFunction);
</script>
<p><strong>Note</strong>: Change type="video/WMV" to type="video/mp4" and then click 'Run' button</p> </body>
</html>