If I'm not mistaken, the unit will not play these files. At leaset not by mirror mode or the like. In the operation manual it says the only type of files that are supported for the feature you're looking for are: MPEG-4, H.264, WMV, MKV and FLV only.
Do you have the AV output setting set to "source"? If so, the same front image should be output the the rear.