It uses ffmpeg and Mencoder. It's extremely versatile, producing H264, divx, MPEG (all #s) encodes - in fact it converts just about anything into anything. It also can take advantage of AVISynth scripts, which is a real bonus.
You need to just take a bit of care about the codecs installed - make sure they don't clash.
Video codecs - http://www.erightsoft.com/SUPERsnap3.html
Audio codecs - http://www.erightsoft.com/SUPERsnap4.html
Regards