Follow the instructions in the link Algus gave. It sounds like you upgraded from an OS where you could rip DVD's. In that case, you should be able to start at the section of the instructions which says:
"Mac users, specifically those running OS X El Capitan" ...
For me, after the upgrade, the libdvdcss.2.dylib was not in the QuarantineRoot directory, but in the usr/lib directory under QuarantineRoot.
I haven't ripped a DVD in ages so I didn't even know that functionality was broken. I haven't tried the instructions but what it says makes sense.
EDIT: Just tried it and it worked. But I did the file navigation in Terminal (easier for me).