Modified script from https://pastebin.com/HS9ukpRm

Twitch-ad-blackout.user.js

// ==UserScript==
// @name        Twitch ad blackout
// @namespace   Twitch ad blackout
// @match       *://*.twitch.tv/*
// @grant       none
// @version     1.0
// @author      https://nitter.net/EthanShulman/
// ==/UserScript==

// Modified script from https://pastebin.com/HS9ukpRm
(function() {

//current state of if video is disabled
var disabledVideo = null,
originalVolume = 0;

//repeatedly check for ad
function checkForAd() {

	//check ad by looking for text banner
	var adBanner = document.querySelectorAll("span.tw-c-text-overlay"),
		foundAd = false;
	for (var i = 0; i < adBanner.length; i++) {
		if (adBanner[i].attributes["data-test-selector"]) {
			foundAd = true;
			break;
		}
	}

	if (foundAd) {
		//if found ad and video is visible, black out video and mute
		if (!disabledVideo) {
			//get livestream video element
			var liveVid = document.getElementsByTagName("video");
			if (liveVid.length) {
				disabledVideo = liveVid = liveVid[0];
				//mute
				originalVolume = liveVid.volume;
				liveVid.volume = 0;
				//black out
				liveVid.style.filter = "brightness(0%)";
        			//speed up
        			document.querySelector('video').playbackRate = 16.0;
			}
		}
	} else {
		//if no ad and video blacked out, unmute and disable black out
		if (disabledVideo) {
			disabledVideo.volume = originalVolume;
			disabledVideo.style.filter = "";
			disabledVideo = null;
      			document.querySelector('video').playbackRate = 1.0;
		}
	}

	setTimeout(checkForAd,100);
}

checkForAd();

}());