We are developing CG application with Decklink SP Card. One of our customers needs key out for sending to an external keyer device. As I understood from the Blackmagic Decklink SDK, external keying feature does this job with IDecklinkKeyer Interface. But it says that it is only for dual SDI output cards. So, we cannot get it with Decklink SP. Which cards range exactly should we use to get seperate key out?