High quality GIF with FFmpeg

• Use palettegen to create a color palette suitable for use across the entire video
• Use paletteuse to convert frames of animation back to the palette

#!/bin/sh

palette="/tmp/palette.png"
filters="fps=15,scale=320:-1:flags=lanczos"

ffmpeg -v warning -i $1 -vf "$filters,palettegen" -y $palette
ffmpeg -v warning -i $1 -i $palette -lavfi "$filters [x]; [x][1:v] paletteuse" -y $2