round.sh

#!/usr/bin/env bash
fd frame | while read line; do
convert $line \
\( +clone  -alpha extract \
           -draw 'fill black polygon 0,0 0,15 15,0 fill white circle 15,15 15,0' \
\( +clone -flip \) -compose Multiply -composite \
\( +clone -flop \) -compose Multiply -composite \
\) -alpha off -compose CopyOpacity -composite $line;
done