JSFiddle - React, Tailwind, and code Playground

HTML

<video id='video' height='100px'>
   <source src=http://techslides.com/demos/sample-videos/small.webm type=video/webm> 
   <source src=http://techslides.com/demos/sample-videos/small.ogv type=video/ogg> 
  <source src=http://techslides.com/demos/sample-videos/small.mp4 type=video/mp4>
  <source src=http://techslides.com/demos/sample-videos/small.3gp type=video/3gp>
</video>
<p id='label'> </p>
<button onClick="compute()">Compute</button>

CSS

body {margin:0; padding:0px;}

JavaScript

window.onload = function() {
   compute();
};

document.getElementById("video").onloadedmetadata = function (e) {
    compute()
};

function compute() {
   var video = document.getElementById('video');
   var width = video.videoWidth;
   document.getElementById("label").innerHTML=width;
};