For example, you could have a device that can only play MP4 videos, and not MKV. To be able to watch your MKV file, you have to know how to convert MKV to MP4 file format.

MKV is an open-source container format that’s useful for storing multiple files using multiple encoding types; many of us use the format when downloading and storing films and TV shows.

I'm going crazy trying to find a way to convert a .mkv file with H264/AAC to an .mp4 file with the same content (so QT can play it natively). VLC's transcoding doesn't work, ffmpeg doesn't seem to ...

You don't have to settle for WMC's lack of MKV file support. Here's how to make Media Center play nice.

MKVToolNix is a set of free tool that allow you to create, alter, split, join and inspect WebM and Matroska video MKV files. Works on Windows as well.