I found this command line online for converting videos to H263
.3gp files in Linux:
ffmpeg -i inputfile.avi -s qcif -vcodec h263 -acodec mp3 -ar 8000 -ab 32 -y outputfile.3gp
It seems to be a bit out of date, as it gives:
WARNING: The bitrate parameter is set too low. It takes bits/s as argument, not kbits/s
Unknown encoder 'mp3'
Those two problems are easily fixed: