More technically, the data on the disk is encrypted with that “password”, so there’s not really a password prompt. It’s more like your DVD player will have this encryption key stored on it somewhere (possibly on a separate chip where it’s hard for somebody to extract it and distribute it on the internet lol), and then it will automatically run the decryption algorithm with this key on the disk contents transparently.
It’s the password to unlock the content on the DVD (well, HD DVD / Blu-Ray) so you can just copy the video from it for redistribution.
How do you get to the password prompt?
More technically, the data on the disk is encrypted with that “password”, so there’s not really a password prompt. It’s more like your DVD player will have this encryption key stored on it somewhere (possibly on a separate chip where it’s hard for somebody to extract it and distribute it on the internet lol), and then it will automatically run the decryption algorithm with this key on the disk contents transparently.