Forcing YT to use advanced tweaks for CPU usage limitations

This userscript will remove the numbers of notifications, semi-advanced CSS tweaks along with forcing all videos to use the h.264 codec rather than VP9/AV1.
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// ==UserScript==
// @name         Forcing YT to use advanced tweaks for CPU usage limitations
// @version      2025.09.28
// @description  This userscript will remove the numbers of notifications, semi-advanced CSS tweaks along with forcing all videos to use the h.264 codec rather than VP9/AV1.
// @author       LegendCraftMC
// @license MIT
// @match        *://www.youtube-nocookie.com/*
// @match        *://www.youtube.com/*
// @match        *://m.youtube.com/*
// @namespace    https://greasyfork.org/en/users/933798
// @icon         https://www.youtube.com/favicon.ico
// @unwrap
// @run-at       document-idle
// @unwrap
// @grant        none
// ==/UserScript==
// Add config flags to disable both animations and ambient mode functionally

// Enable strict mode to catch common coding mistakes
"use strict";

// Define the flags to assign to the EXPERIMENT_FLAGS object
const flagsToAssign = {
  // Disable animated features (except for sub and like buttons)
  web_animated_actions: false,
  web_animated_like: false,
  web_animated_like_lazy_load: false,
  smartimation_background: false,
  // Disable ambient lighting
  kevlar_measure_ambient_mode_idle: false,
  kevlar_watch_cinematics_invisible: false,
  web_cinematic_theater_mode: false,
  web_cinematic_fullscreen: false,
  enable_cinematic_blur_desktop_loading: false,
  kevlar_watch_cinematics: false,
  web_cinematic_masthead: false,
  web_watch_cinematics_preferred_reduced_motion_default_disabled: false,
  // More tweaks
  kevlar_refresh_on_theme_change: false
};

const updateFlags = () => {
  // Check if the EXPERIMENT_FLAGS object exists in the window.yt.config_ property chain
  const expFlags = window?.yt?.config_?.EXPERIMENT_FLAGS;

  // If EXPERIMENT_FLAGS is not found, exit the function
  if (!expFlags) return;

  // Assign the defined flags to the EXPERIMENT_FLAGS object
  Object.assign(expFlags, flagsToAssign);
};

// Create a MutationObserver that calls the updateFlags function when changes occur in the document's subtree
const mutationObserver = new MutationObserver(updateFlags);
mutationObserver.observe(document, { subtree: true, childList: true });

// Hide the number of notifications to prevent any annoyances
// Save the original descriptor of document.title
const originalTitleDescriptor = Object.getOwnPropertyDescriptor(Document.prototype, 'title');

// Create a custom getter and setter
Object.defineProperty(document, 'title', {
  get: function() {
    return originalTitleDescriptor.get.call(this);
  },
  set: function(newValue) {
    // Remove the (#) with regex.
    const interceptedValue = newValue.replace(/^\(\d+\)\s?/, "");

    // Call the original setter
    originalTitleDescriptor.set.call(this, interceptedValue);
  }
});

(function() {
    'use strict';
    const style = document.createElement('style');
    style.type = 'text/css';
    style.innerText = '.yt-spec-icon-badge-shape--type-notification .yt-spec-icon-badge-shape__badge{display:none;}';
    document.head.appendChild(style);
})();


// Force all videos to use h.264 (useful if you have a low spec machine when you load videos in 720p60)
// Modified from https://github.com/erkserkserks/h264ify/tree/master/src/inject as of 2018-05-16 (MIT license)

var mse = window.MediaSource;
if (mse){
  // Set up replacement for MediaSource type support function
  var nativeITS = mse.isTypeSupported.bind(mse);
  mse.isTypeSupported = ourITS(nativeITS);
}
// Here's the replacement
function ourITS(fallback){
  // type is a string (hopefully!) sent by the page
  return function (type) {
    if (type === undefined) return '';
    // We only reject VP9
    if (type.toLowerCase().indexOf('vp9') > -1) return '';
    if (type.toLowerCase().indexOf('vp09') > -1) return ''; // Added 12/20/2019
    // Let Firefox handle everything else
    return fallback(type);
  };
}

// Add CSS tweaks (disables frosted glass transparency on topbar to revert back to the old topbar color, reducing the bottom gradient in the video player, etc...)
(function() {
let css = `
/* Topbar tweaks */
ytm-mobile-topbar-renderer.frosted-glass,
ytm-pivot-bar-renderer.frosted-glass,
ytm-feed-filter-chip-bar-renderer.frosted-glass,
#background.ytd-masthead, #frosted-glass.ytd-app,
#left-arrow-button.ytd-feed-filter-chip-bar-renderer,
#right-arrow-button.ytd-feed-filter-chip-bar-renderer {
background: var(--yt-spec-base-background) !important;
backdrop-filter: none !important;
-webkit-backdrop-filter: none !important
}

#left-arrow.ytd-feed-filter-chip-bar-renderer:after {
background: linear-gradient(to right, var(--yt-spec-base-background) 20%, rgba(255, 255, 255, 0) 80%) !important
}

#right-arrow.ytd-feed-filter-chip-bar-renderer:before {
background: linear-gradient(to left, var(--yt-spec-base-background) 20%, rgba(255, 255, 255, 0) 80%) !important
}

ytd-button-renderer.ytd-feed-filter-chip-bar-renderer {
background: transparent !important
}

div#end.style-scope.ytd-masthead .yt-spec-icon-badge-shape--style-overlay.yt-spec-icon-badge-shape--type-cart-refresh .yt-spec-icon-badge-shape__badge {
color: #fff !important
}

.yt-spec-icon-badge-shape--type-notification .yt-spec-icon-badge-shape__badge {
display: none !important
}

/* Player tweaks */
#cinematics.ytd-watch-flexy {
display: none !important
}

.ytp-gradient-top, .ytp-gradient-bottom {
height: 61px !important;
padding: 0
}

.ytp-small-mode .ytp-gradient-bottom {
height: 54px !important
}

.ytp-big-mode .ytp-gradient-top, .ytp-big-mode .ytp-gradient-bottom {
height: 0 !important
}

.ytp-gradient-top {
background: linear-gradient(to bottom, #0009, #0000) !important
}

.ytp-gradient-bottom {
background: linear-gradient(to top, #0009, #0000) !important
}

/* Remove every unwanted compact renderer in related section and limit the number of related videos to 9 (plus it disables the 'endless scrolling' feature) */
#related ytd-compact-video-renderer,
#related ytd-compact-playlist-renderer,
#related ytd-compact-radio-renderer,
#related yt-lockup-view-model,
#related ytd-channel-renderer,
ytd-watch-flexy ytd-reel-shelf-renderer,
ytd-watch-flexy ytd-rich-section-renderer,
#related ytd-continuation-item-renderer,
#related #continuations {
display: none !important
}

#related yt-lockup-view-model:nth-of-type(1),
#related yt-lockup-view-model:nth-of-type(2),
#related yt-lockup-view-model:nth-of-type(3),
#related yt-lockup-view-model:nth-of-type(4),
#related yt-lockup-view-model:nth-of-type(5),
#related yt-lockup-view-model:nth-of-type(6),
#secondary #related yt-lockup-view-model:nth-of-type(7),
#secondary #related yt-lockup-view-model:nth-of-type(8),
#secondary #related yt-lockup-view-model:nth-of-type(9) {
display: flex !important
}

/* Remove minimal annoyances and other tweaks */
ytd-ad-slot-renderer,
ytm-ad-slot-renderer,
ad-slot-renderer,
ytd-promoted-video-renderer,
ytm-promoted-video-renderer,
ytd-promoted-sparkles-web-renderer,
ytm-promoted-sparkles-web-renderer,
ytd-text-image-no-button-layout-renderer,
ytm-text-image-no-button-layout-renderer,
ytd-merch-shelf-renderer,
ytd-compact-movie-renderer,
ytd-mealbear-promo-renderer,
ytd-video-quality-promo-renderer,
tp-yt-iron-overlay-backdrop.opened {
display: none !important
}

.ytd-ghost-grid-renderer,
.info-skeleton,
.meta-skeleton,
#ghost-cards,
#ghost-comment-section,
#related-skeleton {
display: none !important
}

ytd-watch-metadata.ytd-watch-flexy {
padding-bottom: 36px !important
}`;
if (typeof GM_addStyle !== "undefined") {
  GM_addStyle(css);
} else {
  let styleNode = document.createElement("style");
  styleNode.appendChild(document.createTextNode(css));
  (document.querySelector("head") || document.documentElement).appendChild(styleNode);
}
})();