When I start iTunes, it automatically syncs with my Apple TV. And every time it does that I get an error: Then it lists the files in question and they are all audiobooks, books I got pre-iTunes from Audible.com and then later imported into iTunes. Because they are pre-iTunes audiobooks, they have the .aa extension instead of .m4b. Those are the ones that give me the error message. Now I don't actually want ANY audiobooks to transfer to Apple TV (makes no sense to me to have them there) but there is no Book tab for Apple TV. When I called this problem into Apple, I pointed out that it would be nice to have this option so that I could simply turn off the syncing of audiobooks. Since that doesn't seem to be possible right now, my next option is to convert these files from .aa to .m4b. Then they would sync just fine (not that I want them over there), and I would at least not have to deal with an error message every time I start iTunes. The Apple rep suggested I search for .aa to .m4b converters, though noted that he could not officially recommend that. So I've been poking around on Google and I see the wasteland of warez cracks and the like that such searches take me to. A lot of the utilities are Windows .exes which doesn't do me any good. So can anyone suggest a) How to prevent Apple TV from thinking it should sync my audiobooks; or b) how under OS X to convert an .aa file to .m4b (or, I suppose, just .mp3 would do)?