use ffcast to record either a gif or mp4 from rectangle selection using slop. set the stop/start execute of this script to a hotkey.

screen_record_with_rect.sh

#!/usr/bin/env bash
# use ffcast to record either a gif or mp4 from rectangle selection using slop
# required: ffmpeg,ffcast,imagemagick,slop
# set the stop/start execute of this script to a hotkey.
function usage() {
	echo "Usage :  $(basename "$0") [options] [--]

    Options:
    -k|kill    kill last running record
    -r|record  start recording
    *          toggle starting/stopping recording with no arguments
		"

} # ----------  end of function usage  ----------

kill_record() {
	pkill -fxn '(/\S+)*ffmpeg\s.*\sx11grab\s.*'
}

record() {
	choice=$(echo "mp4,gif" | tr ',' '\n' | rofi -dmenu)
	TMP="/tmp/$(date '+%Y-%m-%d.%H:%M:%S')"

	if [[ "$choice" = "mp4" ]]; then
		ffcast -q -g $(slop -n -f '%g') rec $TMP.mp4
		notify-send "$TMP.mp4"
		echo -n "$TMP.mp4" | xclip -selection clipboard
	elif [[ "$choice" = "gif" ]]; then
		trap "rm -f $TMP.avi" EXIT
		ffcast -s % ffmpeg -y -f x11grab -show_region 1 -framerate 15 \
			-video_size %s -i %D+%c -codec:v huffyuv \
			-vf crop="iw-mod(iw\\,2):ih-mod(ih\\,2)" $TMP.avi
		convert -set delay 10 -layers Optimize $TMP.avi $TMP.gif
		notify-send "$TMP.gif"
		echo -n "$TMP.gif" | xclip -selection clipboard
	fi
}

toggle() {
	if pgrep "ffmpeg"; then
		kill_record
	else
		record
	fi
}

while getopts ":krh" o; do
	echo $o
	case "${o}" in
	k)
		kill_record
		exit 0
		;;
	r)
		record
		exit 0
		;;
	h)
		usage
		exit 0
		;;
	esac
done

if [ $OPTIND -eq 1 ]; then
	toggle
fi
exit 0