This directory holds git submodules that point to libraries needed by the WebM and WebP plug-ins.
You will need to manually add the following to this directory because the owners don't have a git repository I can embed:
If the submodule contents are missing, you should be able to get them by typing:
git submodule init
git submodule update
Both Mac and Windows require the "yasm" shell program be installed for libvpx to compile. On Windows you get it via Cygwin.