I've got three boxes running MC 12. On all three, I've set up MC to use DirectShow for MP4 and M4V files, then library-imported two videos encoded in Xvid with MP4 containers. On two of the three boxes, when I double-click the MP4 videos, MC plays the files. On one of the boxes, despite the DS settings, MC tries to use QuickTime instead -- I know this because I get a dialog from QuickTime saying it can't recognize the video type and wants to install more files. However, if I go to the file manager in Vista, select the videos, then right-click and select Media Center > Play, the videos play. So, it's as if MC treats the files differently if they're in the library than if they're passed in using the shell extension. The box in question is running a new install of Vista, CCCP, and MC12.
I removed the files from the library, then tried it again, but had the same results. One of the reasons I bought MC was to be able to use its video library features, so this is a bit annoying.
Thoughts?