Is this possible? Say, saving only the central 50% crop when shooting with full resolution silent picture? This could be used for example for 8mm film scanning (frame by frame, with a macro lens), where the full sensor resolution is an overkill, plus one can only fit ~2 minutes of 8mm film on a 64GB card.
You can use pre record and halfshutter trigger with any chosen movie mode. It would work as suggested only it would record into a mlv file. Export to dng if you like in post.