VitualDubMod is able to handle mkv files: Find it
here.
Other method to get data about the streams muxed to the container is to use
gspot.
It is also capable of showing the codecs installed on your system.
Under add/remove programs you'd only see entries of codecs installed through an installer routine with deinstall option.
Often filters get only copied to your system dir and then registered for use in DirectShow.