JSFiddle - React, Tailwind, and code Playground

HTML

<h1>
  Video Resolution Size Detection
</h1>
<p data-content="resolution"></p>
<video src="https://bug1250345.bmoattachments.org/attachment.cgi?id=8722238"></video>

JavaScript

document.querySelector('video').addEventListener('resize', (e) => {
  document.querySelector('[data-content="resolution"]').textContent = [e.target.videoWidth, e.target.videoHeight].join('x');
});