Yeah I have a bash script that does similar, using the notification API for interactivity

FOLD_CAMERA=CameraShots
TEMP_PID=~/.record_pid
APP_ID=record

mkdir -p $FOLD_CAMERA

function main {
    termux-notification \
        --id $APP_ID --group RECORD \
	    --priority max \
	    --button1 "Front" \
	    --button1-action "termux-notification-remove $APP_ID;bash $0 record 1" \
	    --button2 "Back"  \
	    --button2-action "termux-notification-remove $APP_ID;bash $0 record 0" \
	    --button3 "Quit" \
	    --button3-action "termux-notification-remove $APP_ID;exit" \
	    --title "Record"
	
}

function record {
    local cam=${1:-0}

    termux-notification \
        --id $APP_ID --group RECORD \
	    --priority max \
	    --button1 "Stop" \
	    --button1-action "termux-notification-remove $APP_ID; bash $0 killproc" \
	    --title "Rec. $cam"
    
    (while :; do
	     termux-camera-photo \
	         -c $cam \
	         $FOLD_CAMERA/$(date "+%Y%m%d-%H%M_${cam}_record.jpg")
     done) &

    local pid=$!
    echo -n $pid > $TEMP_PID
} 

function killproc {
    local last_pid=$(cat $TEMP_PID)
    if [ "$last_pid" == "" ]; then
	    termux-toast "Could not kill process. Restart the phone."
    else
	    kill $last_pid &&
	        bash $0 main
    fi
}


[ "$*" = "" ] && main || eval "$*"

It just needs ffmpeg tied to the exit function