TMP=.
SRC=countdown.mp4
DST=output.mp4
FREEZE_S=10

cd "$TMP"

FRAMERATE=$(ffprobe -v 0 -of csv=p=0 -select_streams 0 -show_entries stream=r_frame_rate "$SRC")

ffmpeg  -i "$SRC"  -vf "select='eq(n,364)'"  -vframes 1  LAST_FRAME.PNG

ffmpeg  -loop 1  -framerate 1  -i LAST_FRAME.png  -r "$FRAMERATE"  -t "$FREEZE_S"  -pix_fmt yuv420p  LAST_FRAME.mp4

printf "file %q\n" "$SRC" LAST_FRAME.mp4  > list.txt

ffmpeg  -y  -f concat  -safe 0  -i list.txt  -c copy  "$DST"