Xbox 360 - unplayable content

[wozza]

Hi

I recently got a new Xbox 360 and was hoping to be able to view my video collection via Mezzmo. However, I get an "unplayable content" error - it's saying the audio or video or using an unsupported codec.

All my videos are AVIs with h.264 & AC3 5.1 audio, so as far as I can tell, they should play natively. Or am I mistaken?

I'm using 2.1.12 BTW

EDIT: actually I also have a few MKVs on the server (same video/audio codecs) but they don't show up on the xbox at all.

Cheers