$ ffmpeg -i test.jpg test.out ... test.jpg: Unknown format
you'll probably want to use 'convert' from ImageMagick. I'm pretty sure convert can change a jpeg into a raw YUV frame.
You can also use mencoder, part of the mplayer package. In older versions, something like this -
mencoder frames/\*.jpg -mf on:fps=4 -o movie.avi -ovc lavc
and in newer versions, something like this - mencoder 'mf://frames/*jpg' -mf type=jpeg:fps=4 -o movie.avi -ovc lavc
will make a movie of all jpeg's in the frames dir, 4 frames per second.
For the OP, using cron, `date +format`, `wget -O`, mencoder and a little shell scripting will work.
Good luck,
-f http://www.blackant.net/
