// ==UserScript==
// @name YouTube H.264 (h264ify clone) 
// @namespace https://www.youtube.com
// @version 17112023
// @description https://github.com/erkserkserks/h264ify
// @match *://*.youtube.com/*
// @match *://*.youtube-nocookie.com/*
// @match *://*.youtubekids.com/*
// @license MIT
// @grant none
// @run-at document-start
// @downloadURL none
// ==/UserScript==

// false or true
let block60fps = true;

function h264ify() {
    // Override video element canPlayType() function
    var videoElem = document.createElement('video');
    var origCanPlayType = videoElem.canPlayType.bind(videoElem);
    videoElem.__proto__.canPlayType = makeModifiedTypeChecker(origCanPlayType);

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

  // 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) return '';
      var disallowed_types = ['webm', 'vp8', 'vp9', 'av01'];
      // If video type is in disallowed_types, say we don't support them
      for (var i = 0; i < disallowed_types.length; i++) {
        if (type.indexOf(disallowed_types[i]) !== -1) return '';
      }

      if (block60fps) {
        var match = /framerate=(\d+)/.exec(type);
        if (match && match[1] > 30) return '';
      }

      // Otherwise, ask the browser
      return origChecker(type);
    };
  }

h264ify();