Some of the MKVs I have cause Vegas to spin eating up CPU and others work fine. Sometimes Vegas blows up and sends me to a url which then asks me to download 17.0.0.452 which is an older version.
version 17 at this time I am not looking to upgrade. Mediainfo I will check that out.
Originally awhile back I saved everything as mkv and import worked and then I would render to MP4 or what was necesssary. This time with these issues, I converted to AVI or MP4. Ok just remembered, vegas would not load up the .mkv so using its' Mediainfo won't work.
MKV is a container, not a format. That means one could put hundreds of different codec combinations in the wrapper, and some of them "may" work in Vegas 17, depending on the decoders available.
Since you are not going to upgrade, your other option is to convert the problem files in Shutter Encoder or Handbrake.
Many people like to know what's inside their MKV "mystery" files, so the MediaInfo utility is something we use to do that. It is downloaded from Sourceforge.