I tested minidlna with some mkvs on a Sharp Aquos Smart TV. It ignores all mkvs.
After checking the traffic with wireshark and comparing it to ushare (with which, the Sharp TV sees mkvs), if found out that it has the same problem as the SonyBDP. It expects video/mpeg as mime type instead of video/x-matroska.
After monkeypatching the source and always send video/mpeg as mime type for mkvs instead of video/x-matroska, it found the mkvs.
This should probably be fixed. I will post some more details (wireshark dumps, user agent, etc. if necessary.