scripts/rec: allow selecting a screen region

scripts/rec

@@ -1,18 +1,24 @@
 #!/bin/sh
 
 record() {
+  if test "$1" = "-s"; then
+    geometry=$(hacksaw -f 'crop=%w:%h:%x:%y,scale_vaapi=%w:%h')
+  else
+    geometry='scale_vaapi=1920:1080'
+  fi
+
   sleep 2
   withcap sys_admin -- ffmpeg -f alsa -i recorder \
     -vaapi_device /dev/dri/renderD128 -f kmsgrab -i - -r 60 \
-    -vf 'hwmap=derive_device=vaapi,scale_vaapi=w=1920:h=1080:format=nv12' \
-    -c:v hevc_vaapi -qp 21 \
+    -vf "hwmap=derive_device=vaapi,$geometry:format=nv12" \
+    -c:v hevc_vaapi -qp 21 -rc_mode 1 \
     -c:a libopus -b:a 96k -ac 2 -ar 48000 \
     -y recording.mkv >/dev/null 2>&1
 }
 
 if test ! -f recording.mkv; then
   echo recording in 2s...
-  record &
+  record "$@" &
 else
   pkill ffmpeg
   echo stopped recording