Info on a slack-desc file is here...
http://slackwiki.org/Slack-descIf you are just building for yourself you do not have to have one. It is a requirement for any packages you might want to upload to the repositories.
Just create a text file called slack-desc and copy this .
# HOW TO EDIT THIS FILE:
# The "handy ruler" below makes it easier to edit a package description. Line
# up the first '|' above the ':' following the base package name, and the '|' on
# the right side marks the last column you can put a character in. You must make
# exactly 11 lines for the formatting to be correct. It's also customary to
# leave one space after the ':'.
|-----handy-ruler------------------------------------------------------|
appname: appname (Short description of the application)
appname: <this line is generally left blank>
appname: Description of application - this description should be fairly
appname: in-depth; in other words, make it clear what the package does (and
appname: maybe include relevant links and/or instructions if there's room),
appname: but don't get too verbose.
appname: This file can have a maximum of eleven (11) lines of text preceded by
appname: the "appname: " designation.
appname: License:GPLv2, GPLv3, MIT, BSD, that sort of thing.
appname: Authors:
appname: Website: Link to apps homepage.
Save that somewhere as a template. Then when building just copy it to the directory your building from and make the necessary edits for that package.
If I remember right dvdrip also requires some perl-modules. So be prepared to build a few more dependencies.