Since I'm a mac person, on mac codecs in most cases are included within the app. So there's no bare/empty-shell like wmp that needs codecs to be dwnlded to play what most people will watch. As for what's compatible with what, I don't know. I'd suggest that there should be some form of documentation at the site or with the dwnlded iles that explains what apps the are compatible with. Not everybody likes to read the 'Read Me first' text files.

avi format in its crude form can be a fairly large file & is roughly equivalent to mpeg1 (xcuse the xtremely rough comparison), however avi is like a shell & can include special encoding within it such as divx (search divx on the net/google divx.) Divx is a translation of mpeg4 which is principleee superior to mpeg 1/2.

If these codecs are anything like the QT codecs for mac, then they will apply to all apps that can utilise these types of codecs for video (system wide.) For mac that'd mean anything that can utilise QT movie formats.