[PLUG-TALK] File sizes on movie DVD

[John Jason Jordan]

Recently I have become aware that when you buy a movie DVD the total
bytes on the disk are sometimes as much as 8GB, at least that is what I
see from the GUI file manager and from the command line. Yet I can use
K3b to duplicate the disk on an ordinary 4.7GB blank DVD. Furthermore,
the disks will play in any ordinary DVD player; a dual layer player is
not required.

How do they do this?