In audio CDs the most common means is to create intentionally erroneous data in the disc format to 'confuse' CD drives that try to read it.
Except that such protection only prevents you from playing the CD in a wide range of players, and not from copying it: In order to listen to the CD you have to rip it, using something called Burst Sync mode.
On DVDs the situation is entirely different though, as the data is compressed and thus needs to be error-free also when read by a player, to a reasonable extent. Copy protection such as extra layers can only be implemented to an extent such that all players support it, and it still doesn't prevent you from ripping and decrypting the data that's on the disk, because all you need is the ability to actually read the data.
