We are sure that you have come upon an MKV file that you want to watch and that you haven't been able to because the file is corrupt. Now there is a solution for these cases: Meteorite. This application quickly repairs damaged files. Meteorite doesn't require installation, and its interface is really simple: it's simply a window on which you have to drop the file that's damaged. After that you'll see a progress bar and a short time afterwards, Meteorite will have finished repairing the file and it will have placed it on your desktop.
This is how simple it is to repair the files that you thought were unrecoverable with Meteorite.