Hey brumby,
Windows 7 supports most modern video and audio codecsand container formats. However it doesn’t support Matroska video files as it doesn’t have native mkv splitter. Using DivX plus you should be able to play mkv files. Now if there’s no sound, try installing audio decoder and processor filter from third party source. Please use your favorite search engine and see which one serves the purpose.
Divx Mkv Codec
For more information about codecs, see:
Refer:
I just added some new TV shows to my Plex - in the familiar.mkv format. The video is perfect but there is NO audio if I try to play it anywhere on my home network. I went to my parents house, hopped on the computer and logged into Plex and the audio was there!
Codecs: frequently asked questions
Note: Microsoft cannot guarantee that any problems resulting from the use of Third Party Software can be solved. Using Third Party Software is at your own risk.
Divx Audio Codec
Regards,Shinmila H - Microsoft Support
Divx Codec No Sound Mkv File Software
Visit our Microsoft Answers Feedback Forum and let us know what you think.