Wienier:
I too was stumped trying to figure out why .mkv files would play on Quicktime 7 in Leopard on my home theater mini, but wouldn't play on Quicktime X in Snow Leopard on my upstairs mini, like you said, even with Perian installed. Eventually I found this Perian "tweak" which makes Quicktime realize that it can open .mkv files. Download, unzip, and run this program once:
http://astrange.ithinksw.net/perian/Perian%20-%20Open%20in%20QT%20Player.zip. Quicktime will now be able to open your .mkv files.
For your reference, I found it on this thread:
http://forums.whirlpool.net.au/forum-replies-archive.cfm/1271991.html
As for Plex. it isn't just for playing certain types of files, it is a very powerful home theater media player based on the X-Box Media Center platform. It plays every file format I've thrown at it, from .wmv and .mkv to .m2ts. The controls/interface are there, but you have to install the app and set up your media library and do quite an in-depth setup, etc. It's a fantastic program (best home theater media center I've ever seen for the Mac), but if you're just wanting to individually play .mkv files, probably more than you need.
--Equusz
Message was edited by: Equus
Message was edited by: Equus