Is the OPD local cache individual files for each disk or one single file?
I was playing with the cache folder last night, here's what I discovered:
There's one .dt1 file per disc. The file name is a 12-character hex code, that I suspect is the AACS encryption signature, but I haven't been able to verify that. Makes sense though as it's a unique number on every disc, but I don't know if it's a number that can be read from the disc... Could just be a checksum of sorts based on number of files/file sizes on the disc.
These files are only created for discs with BD+ (Didn't test ScreenPass discs though)
These files are _ALWAYS_ created for any disc inserted that has BD+
AnyDVD will _ALWAYS_ try to contact the online server, and will use the information from the online server, no matter how old the disc is.
If it can't connect to OPD, it will then use it's internal database (if the disc is present), and it will still create the .dt1 file.
I tested this by deleting the cache, unplugging my computer from the internet, inserting a Fox BD+ disc from 2007/2008 and it tried to connect to the OPD, couldn't find it, still created the dt1 file and decrypted the disc. Deleted the cache again, connected the internet, inserted the same disc again, and it used the 'online database', but created the same .dt1 file.
So we could technically accumulate a collection of .dt1 files for every BD+ disc out there, but we really only need them for discs made since about 2014 or so... (I guess, I haven't tried a really recent disc yet.)
I don't have any ScreenPass discs to experiment with, so I'm not sure if those generate these files or not. But it sounds like they don't get cached.