mkv files

It could be 'difficult' forms of Matroska files. FYI Matroska is just a container like MOV or AVI, and some mkv have the video encoded with Real Video Codec (RV9 RV10). Perian+QT can't decode this, but VLC will play .mkv files just fine on OS X, as long as they don't use H.264!

It's a bit of a lottery until Matroska decide to support the Apple platform. I have found this:

http://mkv4mac.free.fr/index.php?lang=en&p=lec

which may help.

But there may be another workaround:

1. Get Info the mkv file
2. Change to extension to wmv. Save as wmv and that could work better.

To add to Klaus1...

Open the System Preference's for Quicktime. Under the Advance Tab...>MIME...>Video... enable Matroska files. This may work and may not. Worth a try.

I have no idea if this works, I never come across Matroska files.

Brewer's right. Enabling 'Matroska' at QT Preferences plays all my mkvs.

You can check all boxes. If something does goes wrong you know where to go to fix it.

You have to watch it too. You can make it to where Quicktime opens PDF's. Just uncheck the box to where Quicktime will not open PDF's.

.MKV is a container format developed by Matroska.
The Matroska Multimedia Container is an open standard free Container format, a file format that can hold an unlimited number of video, audio, picture or subtitle tracks inside a single file. It is intended to serve as a universal format for storing common multimedia content, like movies or TV shows. Matroska is similar in conception to other containers like AVI, MP4 or ASF, but is entirely open in specification, with implementations consisting mostly of open source software. Matroska file types are .MKV for video (with subtitles and audio), .MKA for audio-only files and .MKS for subtitles only. High Definition movies in 720 or 1080 pixel width format are often encoded and packaged as a Matroska format video with a .mkv file extension.

From: MKV Format and How to Play MKV Files on Macs?

The tutorial on Squidoo.com would help you out.
MKV Format and Tips of Playing MKV Files on Mac
http://www.squidoo.com/mkv-converter-mac

Does anyone know how to keep the multichannel sound when converting mkv to mp4?
I'd like to burn my mkv's to DVD as a AVCHD disc WITH DTS or AC3 sound.
It works great with Toast, but I only get stereo sound. :-/