If you mean you are trying to find out the codec detail for a video you have, you can use a tool like ffprobe or mp4box. There is a good description of the meaning of the three hex values in the codec code in this answer here: https://stackoverflow.com/a/16365526/334402
Its not clear from your question if you are trying to understand somehow if a particular browser can play a given video. If this is what you want then the the 'canPlayType' (https://developer.mozilla.org/en-US/docs/Web/API/HTMLMediaElement/canPlayType) check can be useful, but be aware that you will likely get a lot of 'maybes' as it is actually hard to be 100% sure before a video actually starts playing.
var checkVideo = function (event) {
var file = this.files[0]
var type = file.type
var videoNode = document.querySelector('video');
var canPlayResult = videoNode.canPlayType(type);
if (canPlayResult === "") {
canPlayResult = "No"
}
alert(canPlayResult);
}
Note that changing the codec name or code in your HTML5 code will not make the browser start supporting a particular codec type in case this is the perception. The browser's video decoding functions need to actually have support for the given codec (and profile etc) for it to be able to play the video - i.e. someone has to have written the logic to interpret and decode the particular encoding format.