Rather than solving this problem on the server, you can solve it on the client at view time with the HTML5 video
element.
$("#video").bind("loadedmetadata", function () {
var width = this.videoWidth;
var height = this.videoHeight;
// ...
});
Using this approach your upload solution can remain untouched.
If storing the dimensions in the database is a requirement, consider finding a way to leverage the video
element during the upload process. One approach would be to have a video 'preview' step right after upload that would extract the dimensions with the JavaScript code above and post them as hidden form elements to your server.