There are 2 types of video capturing devices supported by OpenBSD, the legacy
bktr(4) based chipsets.. and.. USB Video Class compliant devices, supported by
uvideo(4).
The former is really the only real option for TV capture.. I haven't been able to find any UVC compliant TV tuners, most UVC devices are web cameras.
Still, I'm not aware of any ATSC/Digital tuners.. the developers did decide to implement a Video4Linux compatibility layer as
video(4), so eventually future drivers will be written for such devices.
Sorry..