Matroska File Format

Matroska is a multimedia container format like AVI and aim to be an open standard.
It is open and absolutely free for use. Everyone can get specification easily and develop for their own purpose(personal, research or commercial).
The format adopts EBML(Extensible Binary Meta Language) design for extension flexibility.

There are some free implementations for matroska.
The most famous projectss are libebml & libmatroska released under LGPL.

For most case, LGPL is ok. But for commercial usage and companies, BSD License is prefered.
Before 2007, a parser released under BSD License can be found easily on internet.
But it is hard to get a copy now.
For those who try to get it, you can get it (2 files:MatroskaParser.c MatroskaParser.h)
via aegisub project (whole project released under 3-clause BSD License).

For InputStream implementation reference, mkv_wrap.cpp and mkv_wrap.h can be refered.