found crop mode menu, but what does it mean this 3.5K 1:1

[javismiles]

I finally found the crop submenu on the experimental 4k build,

what is the meaning and purpose of the crop submenu?
for example the 3.5K 1:1 , what does it do?
and the others in  that  submenu? whats its purpose?

and why do i get a 23.975 fps, rather than 24?

thank u so much

[Audionut]

You have a number of other threads where this question would have been suitable.

Please slow down on the number of threads being created.  Borderline spamming of the forum.

Regards.