Have you read and tried what I suggested some 5 posts earlier? (post #54)
Whoops! I thought I read the whole topic, but I think I missed the last page
I've been 'casually' tagging music for a couple of years now. Never really looked into it; jus tagged title and author in an automated way and be done with it. Now I'm trying to archive some discs and I want them properly tagged and I started reading a bit more and it's a damn rabbit hole.
From what I understand, MP3 files use ID3 tags which have a formal standard set of tags. FLAC files on the other hand use Vorbis Comments that only have a specification of how to store the tags and not a specification of predefined tagnames. Thus, you end up with this stupid situation where program A uses tagname A and program B uses tagname B.
I've been trying to find out what the most widely accepted tagname for a disc subtitle is and I can't quite figure it out. In ID3 it's quite straight-forward (at least in ID3 v2.4): TSST for Disc/Set Subtitle. Vorbis Comments on the other hand... it looks like a split between SETSUBTITLE and DISCSUBTITLE and there isn't really a definitive type.
I also came across this mapping table: https://wiki.hydrogenaud.io/index.php?title=Tag_Mapping
What I find curious there is that they're mapping TSST (which I assume stands for S
itle) to WM/SetSubTitle yet they call it DISCSUBSTITLE in Vorbis Comment. Because ID3 specs call it set subtitle I'm inclined to use that too, though I personally think disc subtitle sounds more logical.
I'll try out that Picard script you posed a few posts up and I'll see what situation I end up with