$donen = preg_replace('|\[youtube\]http://www.youtube.com/watch\?v=([a-z0-9?&\\/\-_+.:,=#@;]+?)\[/youtube\]|si','<object width="425" height="355"><param name="movie" value="http://www.youtube.com/v/\\1"></param><param name="wmode" value="transparent"></param><embed src="http://www.youtube.com/v/\\1" type="application/x-shockwave-flash" wmode="transparent" width="425" height="355"></embed></object>',$donen);

$donen = preg_replace('|\[gametrailers\]([a-z0-9?&\\/\-_+.:,=#@;]+?)\[/gametrailers\]|si','<embed src="http://media.mtvnservices.com/mgid:moses:video:gametrailers.com:$1" width="512" height="288" type="application/x-shockwave-flash" allowFullScreen="true" allowScriptAccess="always" base="." flashVars=""></embed>',$donen);

http://www.gametrailers.com/video/review-hd-assassins-creed/707493