libmatroska is a C++ libary to parse Matroska files (.mkv and .mka). It is available in LGPL license as a source code that should compile on many platforms including Windows, Linux, Mac OSX and BeOS. It depends on libebml to work.
Matroska is an audio/video container based on EBML. For more information on Matroska you can have a look at the Matroska specs.
You can also access the source directly from our SVN server via Subversion.