FreeNAS is a NAS platform and as far as I know it doesn't support video capture cards.
Further, video capture cards (and analog cameras) generally suck. IP cameras are nearly a quarter of a century old -- I've got AXIS NetEye 200's from 1996 -- and are generally capable of much higher quality, can run via power-over-ethernet, and you can hook a bunch of them up to a decent switch and have a single uplink to your NAS, rather than trying to hook up a capture card that supports a dozen cameras.