You don’t need any software to download you tube videos in Linux… Just follow these steps and enjoy the flvs 
Step 1. Open the required video in the web browser.
Step 2. Let it start streaming/buffering.
Step 3. Minimise the window and open /tmp.
Step 4. Look for a file flash<something>
Step 5. Drag the file on to your desktop.
Step 6. Once the video is buffered in the browser, the file would have been downloaded.
Enjoy!! Cheers!! 
NOTE – Do Not Close The Browser Window/Tab while doing this. This method works for other similar websites also.
big thanks
for win use http://www.flashvideodownloader.org/