recommendation for software to make mp4 from a few stils (+ audio track)

[Dan Hitt <dan.hitt@gmail.com>]

Could anybody please recommend a piece of free software that can take
a few still images together with an audio track and make an mp4 with
them?

(So i guess it is conceptually something that could produce a timed
slide show, but of course if it offered effects for transition from
one image to the next that would be better.)

Command line or gui would be fine, but i would like something whose
sources were available so that if necessary i could tune it.

Thanks in advance for any clues.

dan