Download youtube ke .flv
Get the video_id from the url. It is the string after v=
Next, you need the t-parameter. You can find it in the HTML source, by searching for &t= and copying what is in between the equal sign (=) and the ampersand (&). Now use the following command to download the video:
wget -O outfile.flv "http://www.youtube.com/get_video.php?video_id=xxxxx&t=xxxxx&fmt=18"
Substitude the x'es by the video_id and the t-parameter. The fmt=18 makes sure the video and audio are not re-encoded. This will improve quality dramatically.