JSFiddle - React, Tailwind, and code Playground

HTML

<video src="https://s3.amazonaws.com/mettavr/dev/VfE_html5.mp4" id="video" controls="true" crossorigin="anonymous" />

JavaScript

var audioCtx = new AudioContext();
var source = audioCtx.createMediaElementSource(document.getElementById('video'));

var gainNode = audioCtx.createGain();
gainNode.gain.value = 0.5;
source.connect(gainNode);
gainNode.connect(audioCtx.destination);