GStreamer Base Plug-ins is a well-groomed and well-maintained 
collection of GStreamer plug-ins and elements, spanning the 
range of possible types of elements one would want to write 
for GStreamer. It also contains helper libraries and base 
classes useful for writing elements. A wide range of video 
and audio decoders, encoders, and filters are included.

This build requires both liboil and gstreamer. Both slackbuilds
are available at slackbuilds.org.