Windows Media Player 12 is what comes with 8.1.
Open WMP > under Help Tab > About WMP it tells you there.
You can try installing the Codecs to view those files from here.
Windows 8/8.1 has a serious lack of Codecs.
http://www.snapfiles.com/get/k-lite-full.html
FYI: During our review, we found that this program offers to install promotional, third party components. Installation of these components is optional but you should pay attention during setup
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Or use a different Media Player:
"VLC Media Player (VideoLAN)"
http://www.snapfiles.com/get/videolan.html
Cheers.