yt-embed.js

javascript:(function() {
    var videoId = /[&?]v=(\w+)/g.exec(window.location.search);
    if (videoId) {
        videoId = videoId[1];
        window.location.href = window.location.origin + '/embed/' + videoId + '?autoplay=1';
    } else {
        videoId = /\/embed\/(\w+)/g.exec(window.location.pathname);
        if (!videoId)
            alert("You're not on a video page dumbass.");
        videoId = videoId[1];
        window.location.href = window.location.origin + '/watch?v=' + videoId;
    }
})();