XBOX 360 MKV files in Windows 7

Can someone help with this issue please.
OS : win 7, 64bit ultimatum
Router : BT 2701HGV-c
media center : Xbox
Network : Ethernet cable to xbox
Media storage : Netgear ReadyNAS Duo, connected to router via ethernet

All my MKV files that are on the NAS are not listed in the XBox media list. I see MP4 files
Do I need to install some codecs on the PC in order to see them?

Thanks

[zip]

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