DVD's are encoded for six different regions around the world. Hollywood's film
studios have been alarmed when DVD started to take off. An encoding principle was introduced, to prevent discs of the latest movies being played in countries where the particular movies have not been brought out at this time.
A digital flag on the disc tells the DVD player where the DVD comes from. The DVD player should play only the permitted DVDs for the region where the DVD player was bought.
This principle is not acceptable for professional and AV installations and a lot of interregional players are available already.
The GPRM and SPRM parameter affect the quality of the viewer's experience in a large way.
There are 16 GPRM, the 'General Parameter Register Memories', that determine viewer interactivity. These sixteen registers are located within the DVD player and have no pre-assigned functions the moment the DVD is inserted into the DVD player. DVD authoring is determining the desired functions by adopting GPRMs in the player. The inserted DVD is using the registers to execute certain commands needed for the interactivity of the user.
There are 24 SPRM, the 'System Parameter Register Memories', which are assigned to the DVD specification. Different SPRM specify for instance the viewer’s language preference, the wide-screen preference (16:9, 4:3, letterbox, etc.) and parental ratings. of the viewer, that is how he wishes to screen 16x9 material, as letterbox, 4:3 pan and scan, or 16x9. As DVD authors, we can’t change system parameters such as a viewer’s language preference or parental rating (SPRM 13) without invading his home and tearing into the player’s setup menu. Of the 24 SPRMs in DVD land, nine are read-only, twelve are read/write, and three are unassigned.