Youtube-dl is a python based platform independent command line tool to download any videos from youtube. In ubuntu, it’s already in the repo just download it using apt-get; others can download it from the authors website http://www.arrakis.es/~rggi3/youtube-dl/. The instructions is pretty straight forward. In the terminal type, youtube-dl “youtube_video_address” this will save the video in flv format with can be viewed with most popular video player like VLC or Mplayer for linux. If you want to save video file to something else you could use the -o option like this: youtube-dl -o video.flv “youtube_video_address”.
Here I am playing the video I just downloaded using youtube-dl with VLC.
If you are curious, the video I downloaded in this example, was Linkin Park – Bleed It Out which you can watch from here: http://www.youtube.com/watch?v=M2MhH6mBg58 and download with youtube-dl if you want.