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Forcing YouTube to use minimal settings for CPU usage reduction

This userscript will disable the numbers of notifications along with forcing all videos to use the h.264 codec rather than VP9/AV1.

// ==UserScript==
// @name         Forcing YouTube to use minimal settings for CPU usage reduction
// @version      2025.09.14
// @description  This userscript will disable the numbers of notifications 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-rendere {
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-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
}`;
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);
}
})();