An userscript to disable AV1 video decodec on youtube

no-av1-video.user.js

// ==UserScript==
// @name         No AV1 Video on Youtube
// @version      1.1
// @description  Disable AV1 video decodec on youtube, inspired by chrome extension https://github.com/Shimmermare/NotYetAV1
// @author       You
// @match        *://*.youtube.com/*
// @match        *://*.youtube-nocookie.com/*
// @match        *://*.youtu.be/*
// @icon         https://www.google.com/s2/favicons?sz=64&domain=youtube.com
// @downloadURL  https://gist.github.com/francistm/4e58e1b7ea81f6d7f2952661bd127bb6/raw/no-av1-video.user.js
// @updateURL    https://gist.github.com/francistm/4e58e1b7ea81f6d7f2952661bd127bb6/raw/no-av1-video.user.js
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    // return a custom MIME type checker that can defer to the original function
    function makeModifiedTypeChecker(origChecker) {
        // Check if a video type is allowed
        return function (type) {
            if (type === undefined || type.indexOf('av01') !== -1) return '';
            // Otherwise, ask the browser
            return origChecker(type);
        };
    }

    // Override video element canPlayType() function
    const videoElem = document.createElement('video');
    const origCanPlayType = videoElem.canPlayType.bind(videoElem);

    const modifiedVideoProperty = Object.getPrototypeOf(videoElem);
    modifiedVideoProperty.canPlayType = makeModifiedTypeChecker(origCanPlayType);

    Object.setPrototypeOf(videoElem, modifiedVideoProperty);

    // Override media source extension isTypeSupported() function
    const mse = window.MediaSource;
    // Check for MSE support before use
    if (mse === undefined) {
        return;
    }

    const origIsTypeSupported = mse.isTypeSupported.bind(mse);
    mse.isTypeSupported = makeModifiedTypeChecker(origIsTypeSupported);
})();