ASP.Net: Enable Button after Video Ends using JavaScript

How you are embeding the you tube video.?

If you are using HTML5 Video tag then, use the end event handler.

<input type="button" id="myButton" value="Submit" /><br />
<video id="myVideo" controls src='<%= ResolveUrl("~/Files/1658.mp4") %>' width="200" height="250" />    
<script type="text/javascript">
    window.onload = function () {
        var video = document.getElementById("myVideo");
        var button = document.getElementById("myButton");
        button.disabled = true;
        video.addEventListener("ended", function () {
            button.disabled = false;
        }, true);
    };
</script>

Screenshot