#!/bin/sh

help(){
    cat <<END
Usage: $0 [options] <filename.[mpg]>
END
    exit 0
}

for i in "$@"
do
	case $i in
*.mpg)
		input="$i"\
		base=`echo $input | sed "s/\.mpg$//"` ;;
*)
		help ;;
	esac
	ffmpeg -i $input -vframes 1 -f yuv4mpegpipe -y /dev/stdout |
	y4mscaler -O chromass=444 |
	y4mtoppm |
	pnmtopng >$base.png
done