Youtube seems to disallow that. See their policy.
i wonder if anyone can help me with this query,
I occasionally download a video clip from YOUTUBE,
I normally click the required clip,to play, then if
I move the mouse pointer over the clip, a pop up box
appears, saying DOWNLOAD TO REALPLAYER. It has been
a while since i downloaded anything, but today i tried
to download a music clip. but this time when i hovered
the mouse over the clip, there was no pop up box,
so i right clicked the clip, and it said download to Realplayer BUT WHEN I WENT INTO MY LIABARY THE IMAGE WAS
THERE BUT WHEN I CLICKED TO PLAY THE CLIP NOTHING HAPPENED. I tried the same thing again, but with the same result. Any help at all very much appreciated.