You can use mediainfo to look at info in your files and see what codecs they use etc. This gives more info when reporting files that don’t play on the WDTV.
http://mediainfo.sourceforge.net/en
As has been pointed out only a particular wmv plays on the WDTV. As to avi’s, it all depends on what they contain. There are a huge number of freeware programs which can easily convert unplayable types to someting the unit does play.
