youtube_manual_play.user.js

// ==UserScript==
// @name           YouTube Manual Play
// @include        http://www.youtube.com/watch*
// @include        http://youtube.com/watch*
// ==/UserScript==

(function(){
	var player = document.getElementById('movie_player');
	if(!player)
		return;

	var values = {
		autoplay : 1,
		enablejsapi : 1,
		iv_load_policy : 3,
		fs : 1,
		vq : 'large', // medium large hd720 hd1080
		invideo : false,
	}
	var clone = player.cloneNode(true).wrappedJSObject;
	var vars = player.getAttribute('flashvars');
	for(var key in values){
		vars = vars.replace(new RegExp(key + '=.+?(&|$)', 'g'), '') + 
			'&' + key + '=' + values[key];
	}
	clone.setAttribute('flashvars', vars.
		replace(/&&/g, '&').
		replace(/[\&\?]?(ad_|infringe|invideo|watermark)([^=]*)?=[^\&]*/gi, '').
		replace(/(^[\&\?]*)|([\&\?]*$)/g, ''));
	player.parentNode.replaceChild(clone, player);
	player = clone;

	var iid = window.setInterval(function(){
		if(player.getPlayerState && player.getPlayerState()==1){
			clearInterval(iid);
			
			player.seekTo(0);
			player.pauseVideo();
		}
	}, 100);
})();