[FFmpeg-user] crop filter options

[Yellow Penguin]

It says in the docs for the "crop" filter, you can use "out_w" in "out_h"
and vice versa, but I can't get that to work. Anyone know if this is
actually not possible and a mistake in the docs? When I use the command
'ffmpeg -i test.mp4 -vf "crop=out_h:100:0:0" testout.mp4' I get the message
'Error when evaluating the expression 'out_h''

Obviously, this is a simplified version of the problem. I need a crop with
a size that is a tad complicated, but always square, so it would be nice to
calculate it only once.

Thanks in advance