I tried the following command in the ubuntu for downloading the youtube videos:

youtube-dl "URL"

or if we want to specify the file extension :

youtube-dl -o filename.flv "URL"

This being the most recommended command, doesn't work. It says format is not supported.
Moreover I again tried the command :

wget -c "URL"

But this command also doesn't work . Can anyone help me with this problem???

You can take any URL of the youtube channel. Suppose for example:
http://www.youtube.com/watch?v=_QqT38QRA84

Moreover my adobe flash player is not working because ...
I think its because i tried the command in the terminal :

sudo apt-get update

this tries to get new updates for my ubuntu 10.10 but even though i'm trying a lot to install the new adobe flash player 10 but it's not working. Can you suggest any command that I can type in the terminal to get the adobe flash player 10 through the terminal. Because the terminal is more effective than the "synaptic package manager" or " ubuntu software center" applications... i think so...

I sorry i bothered you so much ... At the time i posted this question the youtube in our network was working but now it's not. When it was working i tried and came to see the error. But I'm really sorry i cannot check it out now. Because the youtube is blocked again in our network. So I cannot say you whether the command youtube-dl -v is really working or not. If youtube again works in our network then I assure you to inform you at once.
And well... thank you for your reply