My VLC Media Player stopped playing MKV videos these days. I checked the settings of VLC and I did not figured out a solution. Who knows other reliable software that can play MKV and other videos?
In order to fix the problem, I recommend you update VLC Media Player to the latest version. If this doesn't help, you can check the database of Mac Informer to find an alternative solution. If you're using a Windows platform, you can try tools like GOM Player, DivX, or MKV Player.
Dan Angel's suggestions are good. Apart from those three alternatives, you can also try 5KPlayer . I have used this free media player for some days;it can play all MKV videos of many different resolutions and sizes.
I recommend you update VLC Media Player to the latest version. If you find an alternative, try Quick Time, Mac Blu-ray Player, or Windows Media Player.