+@item
+To capture only part of a plane the output can be cropped - this can be used to capture
+a single window, as long as it has a known absolute position and size. For example, to
+capture and encode the middle quarter of a 1920x1080 plane:
+@example
+ffmpeg -f kmsgrab -i - -vf 'hwmap=derive_device=vaapi,crop=960:540:480:270,scale_vaapi=960:540:nv12' -c:v h264_vaapi output.mp4
+@end example
+