Vixy.net is an online service for downloading videos from Youtube for PC, Mac, Ipod or PSP. This service allows you to convert youtube videos or Flash Videos to MPEG4 (AVI/MOV/MP4/MP3/3GP) file online.
Enter youtube video in the URL text box and select desired conversion format and click start, for converting FLV files other than youtube, you should provide full url with .flv extension. vixy downloads the video for you and then converts to your selected format and then it gives a popup to save the file to system.
Vixy.net uses open source FLV to MPEG encoder engine. It converts FLV to MPEG4 faster and less lossy than a typical transcoder.
You may be interested to checkout how to download videos from youtube, dailymotion, metacafe