matroskavlc-media-player
When I play mkv file in VLC, it produces this error
No suitable decoder module:
VLC does not support the audio or video format "undf". Unfortunately there is no way for you to fix this.
What does it mean and how to fix it?
My OS is Windows 7.
Thanks and regards!
It says that there is no audio there basically. Which VLC do you use? Does the movie plays with other soundtrack in an other player like mpc-hc(from CCCP pack) ?
If yes, you can try a fresh VLC build like 1.1.0-pre5 or something (or pre4.. if I remember clearly they are at pre5 already).
Further to Crazy Buddy's answer, have a look at using CoreAVC in conjunction with MPC-HC (or even MPC-BE, a fork of the project). CoreAVC, while a commercial solution, includes a rendering engine that is unmatched by VLC or codecs included with the CCCP.
If you go this route, you'll need to load the CoreAVC .ax files (codec files) in the External Filters section of MPC, and you'll need to set it to "prefer". Here is a seudo-example I found on the web: 
Best Answer
This means that VLC doesn't recognize the format of one of the data streams in your MKV file. It can't play this file and considers it unfixable.
Without more details, we can't tell you why VLC thinks the file is broken. You can try:
You might look into MKVtoolnix (for Linux, OSX, Cygwin and Windows) or MKVtools (for OSX). MKVtoolnix is a set of tools for creating, altering, and inspecting MKV files; your MKV may be reparable using them. Start with the following command, and inspect the output for errors; it may give you more information about what's wrong with the file: