Thanks, that's the useful information I was looking for.
MakeMKV does claim to have better BD+ decoding, though it was still not able to handle the Alien discs. I got the same glitches (but the bdplus warning now eliminated) from the backup.
So whilst it seems to have a better go, it does leave me in exactly the same position.
From what I can see, MakeMKV distributes additional 'SVQ' files used to generate 'FUTs' (fix-up-tables); I get the impression this is state information that could even come not from BD+ decoding but from intercepting an official player?
It does seem like my hopes of an open source decoder are rather unlikely :-(
It sounds like it's going to be infeasible for me to contribute, as I'd need to get up to speed with everything that's gone before.
Code:
MakeMKV v1.10.1 linux(x64-release) started
Backing up disc into folder "/home/ehehon/Videos/backup/ALIENS_WW"
Evaluation version, 30 day(s) out of 30 remaining
Error 'Scsi error - ILLEGAL REQUEST:COPY PROTECTION KEY EXCHANGE FAILURE - KEY NOT ESTABLISHED' occurred while issuing SCSI command AD010..080002400 to device 'SG:dev_11:1'
...
Can't read AACS VID from disc - most likely current AACS host certificate is revoked by your drive
Highest AACS version is v19 , MKB saved as /home/mark/.MakeMKV/MKB_v19_ALIENS_WW.tgz
The volume Id is unknown for this disc - BD+ code will likely fail
Automatic SVQ downloading is disabled or failed.
Loaded 424 SVQ file(s)
Processing BD+ code, please be patient - this may take up to few minutes
Processing BD+ code using generic SVQ from builtin/00000.svq
Saved BD+ dump file as /home/ehehon/.MakeMKV/dump_ALIENS_WW_E6363BCA5681E2B0.tgz
Loaded content hash table, will verify integrity of M2TS files.