I can not play .m4v files in Windows 7 Media Center.I am using Windows 7 Professional.
MPEG-4 movie files like .mp4, .mov, and .m4v are natively supported in Windows 7.If it’s DRM protected or protected by FairPlay (itune).You have to tweak registry key if required:-
Log on as Administrator.
In the Start Search Box type in:regedit and press the Enter Key.
Open HKEY_CLASSES_ROOT and expand it and scroll down to .m4v .
Click on .mpv and look at the right pane of the Registry Editor
Make sure Value name PerceivedType must have video as Value data.