I may take another stab at it in the future. One of the (many) problems I've had with it is that quite a few mkv files have improper headers (thus, you can't know, for instance, the frame size and/or video length in seconds). Some simply can't be read at all - I just get black frames.
Note that I'm using Windows API to parse the .mkv files (I can't use ffmpeg from a commercial app). Some may be bugs in how Windows handles .mkv files (and very unlikely to be solved in the near future) and some may be bugs in how .mkv files have been written (and ffmpeg, since it's so mature, may very well ignore "bad" frames and such).
At the time I analyzed this, I considered this more trouble than it's worth. Perhaps I will reconsider this in the future, with the addendum that if I get an error or so, I will disregard the file.