Youtube Downloader HELP

Have you read the YouTube Terms of Service?? If you had, you wouldn't be doing this project.

4. General Use of the Service—Permissions and Restrictions

YouTube hereby grants you permission to access and use the Service as set forth in these Terms of Service, provided that:
A.You agree not to distribute in any medium any part of the Service or the Content without YouTube's prior written authorization, unless YouTube makes available the means for such distribution through functionality offered by the Service (such as the Embeddable Player).
B.You agree not to alter or modify any part of the Service.
C.You agree not to access Content through any technology or means other than the video playback pages of the Service itself, the Embeddable Player, or other explicitly authorized means YouTube may designate.
D.You agree not to use the Service for any of the following commercial uses unless you obtain YouTube's prior written approval:
    - the sale of access to the Service;
    - the sale of advertising, sponsorships, or promotions placed on or within the Service or Content; or
    - the sale of advertising, sponsorships, or promotions on any page of an ad-enabled blog or website containing Content delivered via the Service, unless other material not obtained from YouTube appears on the same page and is of sufficient value to be the basis for such sales.

Violate this and you'll get a nice Cease and Desist letter from YouTubes Legal Department. Keep violating it and they'll take legal action against you.