Any one that makes claim that MKV is a format needs to catch up on the technology.
MKV is a container. You can put all sorts of encoded content in the MKV so you'll want to ask what encoding is supported. The answer is NOT "MKV."
I have a Panasonic DMR-BW835 and I want to play downloaded old movies in the MKV format which it is supposed to support but - some play and some do not play? I convert them from whatever format they are in to MKV in Wondershare Video Converter Ultimate and then burn them with Shampoo Burning studio 11. Any suggestions as to why some play and some don't?