I am not sure exactly what I mean. I remember a year or two ago my daughter had some few dvds that she couldn't get to work on the computer. but worked fine on her dvd player hooked to the tv. Looking at them close, they were just slightly thicker than the others and had a more rounded edge. I don't know what that means. Out of tolerance, more layers, strange format that the computer didn't support? I really couldn't tell you. I never did go to the trouble to get to the bottom of the problem.
Sorry, that's as much as I know.