OK, I will try DVDdecrypter, thank you.
It appears that it still requires the disk to be recognized by the drive, but that could just be the example given.
The DVD's appear to be pressed, but they have been purchased from a kiosk in a shopping mall in Thailand, so who knows? They don't look like any recordable media I'm familiar with.
Ok, DVDdecryptor reports that "Device Not Ready (Logical Unit not ready, Cause not reportable)" which doesn't mean to much to me at this time, though I suspect that by the end of it, I will be pretty clear on a lot of meanings.