This is the script I use to convert rips, youtube vids, or whatever so that I can watch them in Real Player on my Nokia N80 at a later time.
I put it here, so that people searching might find the answer more easily.
Obviously, you'll need ffmpeg installed.
USE="a52 aac amr encode imlib mmx network ogg sdl theora truetype v4l vorbis x264 xvid zlib" emerge -v ffmpeg
This uses 24 fps @ 350kb/s mpeg4 video, and 32kb/s 16kHz AAC mono audio. You can tweak as you like.
if [[ ! -f "$1" ]] then echo $1 doesnt exist exit fi ffmpeg -i "$1" -ar 16000 -ac 1 -acodec aac -vcodec mpeg4 -s 352x288 -r 24 -b 350 -ab 32 "$1.3gp"
It's supposed to support (the superior?) h264, but my newer version of the firmware doesn't, though another N80 with an older version does.
This looks a bit odd on anything that isn't already in a 4:3 format, but pah.