# files in directory: 000000.jpg, 000001.jpg, 000002.jpg, etc.
ffmpeg -i "%06d.jpg" -vf palettegen palette.png
ffmpeg -v warning -i "%06d.jpg" -i palette.png  -lavfi "paletteuse,setpts=2*PTS" -y out.gif
# generates: out.gif
# question: can the duration per frame be customized? e.g. frame 0: 120ms, frame 1: 130ms, etc.