bookmarklet for youtube (Enhance for youtube)

videoSpeedChanger_bookmarklet

javascript:(function (){  var v = document.querySelector('video');v.playbackRate = 1.0;})();

videoSpeedChanger_youtubeExtension

//switching version
(function (){
		  var v = document.querySelector('video');
		  if (v.playbackRate == 1.0){
		     v.playbackRate = 0.7;
		  }else if (v.playbackRate == 0.7){
		     v.playbackRate = 1.4;
		  }else{
		     v.playbackRate = 1.0;
		  }
		  })();

videoSpeedChanger_youtubeExtensionInitCheck

//unser construction

var launchTimeXXX = launchTimeXXX | 0;
function ytc (){
    var v = document.querySelector('video');
    if (launchTimeXXX){
        //console.log("change:"+launchTimeXXX +" " + v.playbackRate);
        //speed changer
        if (v.playbackRate == 1.0){
            v.playbackRate = 0.7;
        }else if (v.playbackRate == 0.7){
            v.playbackRate = 1.4;
        }else{
            v.playbackRate = 1.0;
        }
    }else{
        //console.log("first check:"+launchTimeXXX +" " + v.playbackRate);
        //first launching : check keyword to play normal speed
        launchTimeXXX++;
        let m = new RegExp("曲|song|ソング|カバー|ミュージック|cover|MV|ＭＶ|作詞|作曲|唄|歌|サッカー|天皇杯|ルヴァンカップ|AFC|UEFA");
        let t = document.getElementsByClassName("title");//document.getElementById("container");//
        let ts,tag;
        if(t){
            //console.log("t len:"+ t.length);
            for (let i =0 ; i < t.length;i++){
                ts= t[i].innerText;
                //console.log(" text:"+t[i].tagName+" :" +ts);
                if (ts.match(m)){
                    v.playbackRate = 1.0;
                    v.loop = true;
                    return;
                }
                tag = t[i].previousElementSibling;
                if (t[i].tagName.toUpperCase() == "H1" && tag){
                    for (let i =0 ; i < tag.children.length;i++){
                        ts= tag.children[i].innerText;
                        //console.log("tag a text:"+tag.children[i].tagName+" :" +ts);
                        if (ts.match(m)){
                            v.playbackRate = 1.0;
                            v.loop = true;
                            return;
                        }
                    }
                }
            }
        }
        //console.log("first check2:"+launchTimeXXX +" " + v.playbackRate);
        let c = document.getElementById("description");
        let cs;
        if (c){
            cs  = c.innerText.substring(0,200);
            //console.log(" text:"+cs);
            if (cs.match(m)){
                v.playbackRate = 1.0;
                v.loop = true;
                return;
            }
        }
    }
}
setTimeout(ytc,200);

You can change play speed at You Tube.

1.Make blank bookmark.
2.Set this script string in URL column.(and title such a "x1.0")
3.Set the bookmark on browser toolbar.
(also making many type and setting bookmarklet into folder("video" folder) is useful.
It is easily to select speed (x0.7 , x1.0 , x1.4, x2.0 , x3.0 ....)

If you use this gist at script (like Enhance for youtube browser extension), don't forget remove "javascript:" strings.

see also : https://stackoverflow.com/questions/3027707/how-to-change-the-playing-speed-of-videos-in-html5

Also you can use this HTML5 video page.
But its code apply to only 1 of first video in page.