An mcf file extension is related to the MCF Media Container file format.
MCF file extension - MCF Media Container file
What is mcf file? How to open mcf files?
The mcf file extension is used for MCF file format. MCF is an open (the specs are available for everybody, free of charge), free (no royalties) data storage format called Movie Container Format (previously also known as Multimedia Container Format). It is developed by experienced video enthuasists and programmers. The format and all software we develop for it will also stay free; it won't be turned into a commercial project once it's popular.
In short it is a file format, like AVI. However, it is also much more than that, having streaming and broadcasting features in the same format. It is not video or audio compression algorithm, but instead just a container that can hold any media inside it. This does include MPEG-4 (XviD and DivX), AC3, Ogg Vorbis, MP3 and the others you may need.
The reason this project was started is that once upon a time the only usable movie format on PC was Microsoft's AVI, which had seen its best days and couldn't really be extended any further. After searching for existing alternates, without success, the MCF project (by the name of TMF in the early ages) was started. Since then there have been some other similar new projects appearing, most notably OGM ("Ogg Media").
As if things wouldn't have been complex enough otherwise, one of MCF's lead developers, Steve Lhomme (robUx4) started to experiment with completely new way of storing data, EBML. He took the MCF format structure and replaced most of its simple binary fields by these EBML fields. After some discussion (he was proposing to replace the almost ready for release MCF with this new system), he started his own project (the date was 2002-12-06), Matroska, to experiment more with his system. Well, then Lasse Kärkkäinen (Tronic), the other of MCF's lead developers had to go to military and because the developers still left weren't comfortable enough for coding software, the MCF development was stalled for six months.
The current status is that OGM and Matroska have working code available and can be played back on Windows and Linux. MCF is about four months behind Matroska in this matter, but we are continuing the project because this format has many technical advantages over all known competitors.