video_playback.user.js

// ==UserScript==
// @name         set video playback rate
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  change the playback rate of the video
// @author       wayou
// @match        *://pan.baidu.com/*
// @match        *://www.zealer.com/*
// @grant        unsafeWindow
// @grant        GM_addStyle
// @grant        GM_info
// @grant        GM_xmlhttpRequest
// @run-at       document-end
// ==/UserScript==

(function() {
  "use strict";
  var wrapper = document.createElement("div");
  wrapper.style.cssText = "z-index:999;position:absolute;top:0;";
  var hint = document.createElement("span");
  hint.innerText = "select video rate:";
  wrapper.appendChild(hint);
  var rates = [0.1, 0.5, 0.8, 1, 1.3, 1.5, 1.8, 2, 2.5];
  var options = rates.map(function(rate) {
    return (
      '<option value="' +
      rate +
      '" ' +
      (rate == 1 ? 'selected="selected"' : "") +
      ">" +
      rate +
      "</option>"
    );
  });
  var select = document.createElement("select");
  select.onchange = function(event) {
    var video = document.querySelector("video");
    if (!video) {
      alert("video not found. check your network or reload.");
    }
    video.playbackRate = event.currentTarget.value;
  };
  select.innerHTML = options;
  wrapper.appendChild(select);
  document.body.prepend(wrapper);
})();