Use the oncanplay attribute to define when an audio/ video is ready to start playing.
Example
You can try to run the following code to learn how to execute a script when the media is ready to start playing −
<!DOCTYPE html>
<html>
<body>
<video id = "myid" width = "320" height = "176" controls oncanplay="display()">
<source src = "/html5/foo.ogg" type = "video/ogg" />
<source src ="/html5/foo.mp4" type = "video/mp4" />
Your browser does not support the video element.
</video>
<script>
function display() {
alert("Video loaded!");
}
</script>
</body>
</html>