sudo gainroot
vi /usr/bin/youtube-dl-x

change this line

const_video_url_real_str = 'http://www.youtube.com/get_video?video_id=%s&t=%s&fmt=6' not this line
const_video_url_str = 'http://www.youtube.com/watch?v=%s&fmt=6'

works with fmt=6, fmt=18 seems to work as well, but it's too much for mplayer to handle