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YoutubeDefaultSpeed

Set a default playback rate for YouTube videos.

目前為 2016-08-01 提交的版本，檢視 最新版本。

// ==UserScript==
// @name        YoutubeDefaultSpeed
// @namespace   youtubedefaultspeed
// @version     1.1.1
// @author		splttingatms
// @homepage	https://github.com/splttingatms/YouTubeDefaultSpeed
// @description Set a default playback rate for YouTube videos.
// @match       http*://*.youtube.com/*
// @grant       GM_getValue
// @grant       GM_setValue
// @run-at      document-idle
// @noframes
// ==/UserScript==

(function() {
  'use strict';

  var RATE_OPTIONS = ["0.25", "0.5", "1", "1.25", "1.5", "2", "2.2", "2.5", "2.7", "3"];
  var RETRY_DELAY_IN_MS = 100;

  function getElement(query, callback) {
  	var element = document.querySelector(query);
    if (element === null) {
      // null possible if element not loaded yet, retry with delay
      window.setTimeout(function() { getElement(query, callback); }, RETRY_DELAY_IN_MS);
    } else {
      callback(element);
    }
  }

  function setPlaybackRate(rate) {
    // video element can force unofficial playback rates
    getElement("video", function (video) {
    	video.playbackRate = rate;
    });

    // movie_player div controls the displayed "Speed" in player menu
    // note: does not show values beyond official list
    getElement("#movie_player", function (player) {
      player.setPlaybackRate(rate);
    });
  }

  function setPlaybackRateToPreference() {
      var preferredRate = GM_getValue("playbackRate", 1); // default to 1 if not set yet
      setPlaybackRate(preferredRate);
  }

  function onElementSourceUpdate(target, callback) {
    var MutationObserver = window.MutationObserver || window.WebKitMutationObserver || window.MozMutationObserver;
    var observer = new MutationObserver(function (mutations) {
      mutations.forEach(function (mutation) {
        callback();
      });
    });
    observer.observe(target, {attributes: true, attributeFilter: ["src"]});
  }
  
  function handleRateButtonClick(rate) {
    GM_setValue("playbackRate", rate);
    setPlaybackRate(rate);
  }
  
  function injectButtons() {
    var head = document.getElementById("yt-masthead-user");
    
    var form = document.createElement("form");
    
    RATE_OPTIONS.forEach(function (rate) {
      var input = document.createElement("input");
      input.type = "radio";
      input.name = "playbackRate";
      input.id = "playbackRate" + rate;
      input.onclick = function () { handleRateButtonClick(rate); };
      input.checked = (rate == GM_getValue("playbackRate", 1));
      var label = document.createElement("label");
      label.htmlFor = "playbackRate" + rate;
      label.innerHTML = rate;
      label.style = "margin-right: 5px";
      form.appendChild(input);
      form.appendChild(label);
    });
    
    head.appendChild(form);
  }
  
  function main() {
    injectButtons();
    setPlaybackRateToPreference();
    
    // YouTube uses AJAX so monitor element for video changes
    getElement("video", function (video) {
      onElementSourceUpdate(video, function () { 
        setPlaybackRateToPreference();
      });
    });
  }
  main();
})();