The media repository is place where all the original files of 3D-Models, textures, sound and all the other game art used in STK. This is necessary because those files are normally too large or even incompatible with the game, so they are shrinked or converted before being shipped with the game. These files are only needed by artist who want to edit the models/textures/etc.
You may obtain the media repository by downloading
with a SVN client
Under Unix, an example checkout command would be:
svn checkout https://svn.code.sf.net/p/supertuxkart/code/media/trunk stk_media_repo
You can also browse the repository online at sourceforge.