Needs a way to reliably detect that something is a DVD and not a special CD, basically.
Well, technically we might even have a use for DVD IDs now.
We do need to detect if we have a DVD and handle that differently, though.
With the data-tracks branch (LIB-7) it should be easy to give an error for discs that don't have any audio tracks (data CDs or DVDs).
I should also note: DVDs turn up for libdiscid as audio CDs with one data track and no multisession flag set.
This should be fixed with https://github.com/metabrainz/libdiscid/commit/f0dd84b797c15f5cfb120e77d8f650a0619810b8 and merged to master together with the LIB-7 branch.