Youtube-dl is a handy tool for downloading YouTube video file in linux.It was written and actively maintained by Ricardo Garcia Gonzalez which allows you to download a YouTube video directly as a .flv file which can be played with mplayer or VLC.
Download the Youtube-dl:http://www.nuxified.org/system/files/youtube-install.sh
1.right-clicking on the file, then "properties"->"permissions"->check "allow executing file as a program"
2. Run the youtube-install script in the terminal as root (e.g. sudo ./youtube-install.sh)
It is very easy to use the Youtube-dl, just implement youtube-dl URL in the Terminal where "URL" is your YouTube video URL,eg: