They did exist back in 1996, but only as prototypes, IIRC. I remember reading about them in MacAddict back in 1997. The very first consumer DVD gear started showing up in very, very late 1997, from what I remember.

For the record, OS 8.1 will recognise a DVD-ROM, but not 8.0, though it may, if you steal a copy of the Apple CD/DVD driver from 8.1. No guarantees though.