MPEG-4/MP3 encoder help

What is the best option (application) for converting an AVI to MPEG4
video with MP3 audio?
This is not a normal combination for MPEG-4 video. Quicktime Pro, and
other applications I've looked at, create MPEG-4 video with AAC
audio.
Would someone provide a brief overview of the software and process
they use to create an MPEG-4/MP3 video.

Thanks, E.W.