aTube Catcher is a fully functional media conversion tool which can convert your downloaded video files to many different formats included audio-only or different video formats. It is a free, but ad-supported management downloading application that's well-designed, easy-to-use and attractive.
Here are some screenshots to illustrate the features and user interface of this application:
Any Video Converter
Monkey's Audio
StaxRip
Total Video Converter
Audials Tunebite Platinum