If H.264-encoded video (e.g. security camera recordings) or AAC-encoded audio (frequently found in MPEG4/MP4 videos) don’t play right (no video or no audio) on Windows 2008 R2 / XA 6.x, then you probably need this update to the “Desktop Experience” feature (which you installed to get Media Player, among other things). Works like a charm, adds the missing decoders, no reboot required (it’s adding stuff, not replacing anything).
FIX: You cannot play back an H.264 video file or an AAC audio file on a computer that is running Windows Server 2008 R2 with the Desktop Experience feature enabled
Strangely enough (or is it?), without this hotfix, the affected media files won’t play right even if they play correctly on your client machine and the XA 6.x Windows Media Redirection feature is enabled and functioning, i.e. XA appears to need the decoder even though it’s in theory only streaming the raw media to the client where the actual decoding is supposedly performed.
Thanks Jacques Bensimon for the tip!