Convert video to images per N frame

video_to_image_per_frame.sh

#!/bin/bash
if [ $# -lt 1 ]; then
    echo "${0} requires more than 1 arguments"
    echo "${0} input [output] [framestep]"
    exit 1
fi

INPUT=${1}
OUTPUT=${2:-img%03d.jpg}
FRAMESTEP=${3:-1}

mkdir -p "${OUTPUT%/*}"

CMD="ffmpeg -i ${INPUT} -an -vsync 0 -vf framestep=${FRAMESTEP} ${OUTPUT}"
# echo ${CMD}

echo -n "convert ${INPUT} to ${OUTPUT} every ${FRAMESTEP}-th frame [Y/n] "
read YN

case ${YN} in
    "" | "Y" | "y" | "yes" | "Yes" | "YES") ${CMD};;
    *) echo "noop";;
esac