Its not simply hacking it im affraid; they are extending it. Hacks make use of certain "bugs" in parsers or unclarity in the specs. But these DivX AVIs are not really AVIs anymore, they go beyond the specs. They probably will be backward compatible (where the subs and menus are not shown) though, since an AVI parser must ignore junk data. The situation is similar to what Vidomi has done in the past i think. (I'm just speculating though, but I don't think they'll use alexnoe's way of implementing subs) Perhaps someone should come up with some sort of naming convention though (preferably DivX), since simply calling these files AVI is a bit confusing. Perhaps something like "extended AVI" or "DivX AVI" would do.