video_speed_controls.user.js

// ==UserScript==
// @name video_speed_controls
// @match *://www.youtube.com/*
// @match *://pr0gramm.com/*
// @match *://www.amazon.de/*
// @match file:///*
// @grant none
// ==/UserScript==

const traverse_videos = (f) => {Array.from(document.getElementsByTagName("video")).forEach(f)};

document.addEventListener(
  "keydown",
  (event) =>
    {
      if (event.target instanceof HTMLInputElement || event.target instanceof HTMLTextAreaElement) {return;}
      switch (event.key) {
        case "p":
        case "e": {
          traverse_videos(v => {v.playbackRate += .25});
          break;
        }
        case "[":
        case "w": {
          traverse_videos(v => {v.playbackRate -= .25});
          break;
        }
        case "-":
        case "2": {
          traverse_videos(v => {v.playbackRate = 2});
          break;
        }
        case "0":
        case "3": {
          traverse_videos(v => {v.playbackRate = 3});
          break;
        }
        case "4": {
          traverse_videos(v => {v.playbackRate = 4});
          break;
        }
        case "=":
        case "1": {
          traverse_videos(v => {v.playbackRate = 1});
          break;
        }
        case "x": {
          traverse_videos(v => {v.fastSeek(v.duration)});
          break;
        }
        case "a": {
          traverse_videos(v => {v.fastSeek(v.currentTime - 12)});
          break;
        }
        case "s": {
          traverse_videos(v => {v.fastSeek(v.currentTime + 12)});
          break;
        }
        default: {
          return;
        }
      }
      event.preventDefault();
      event.stopPropagation();
    },
  true
);