User Guide

216 Chapter 14, Navigation Parameters
About Navigation Parameters
The DVD Specification defines two types of navigation parameters: system parameters, or
SPRMs, and general parameters, or GPRMs. Navigation commands refer to these values
when instructing the DVD player to alter the course of playback, forcing playback
characteristics to remain the same, or restricting playback to specific areas of the disc.
You can set navigation parameters as integers or as flags at the bit level, or as counters that
increase in value for each elapsed second.
Authoring with navigation parameters and commands is similar to using a programming
language. For example, authoring a three-option menu so that it does not allow the viewer
to select the third option until the first and second options have been selected involves the
following steps:
1 Set a parameter to compare to other parameters.
2 Change the value of the parameter.
3 Compare the value of the changed parameter to the value assigned to the option the
viewer is attempting to access.
Learning how to implement these steps requires an investment of time and effort on the
part of the author. The result, a DVD disc that has menus that seem to anticipate the
viewer’s needs, will make the titles more intuitive and seamless.
Navigation parameters make it possible for DVD authors to add levels of navigational control
and interactivity never seen before in a media format as broad-based as DVD. Scenarist is the
only DVD authoring system that enables you to exploit fully the opportunities that
navigation parameters make possible.