Sorry - I guess I should have been more clear. I am looking to create a file that is openable in iTunes. I do know how to make a file open in iTunes normally. I even went to the Add to Library command in iTunes, but each time I tried to bring the mp3 into iTunes, nothing happened. The MP3 I created is obviously not compatible.
But I'm holding out hope that a regular MP3 can be chapterized in a way that is compatible with the most popular music player and the iPod / iPhone / iPad ecosystem - just looking to see if anyone can help with this!
You have a choice: chapterize with AAC, or MP3.
While MP3 features the ability to add arbitrary tags, there's nothing like a standardized chapter marker. So you're not going to get "maximum compatibility" that route. It's just not there. At best the "most popular music player" is going to treat it as a standard, non-chapterized MP3.
AAC is, while perhaps not as broadly compatible as MP3, fairly close. It's an open standard just like MP3. And, at least in iTunes and on iPhones/iPods, it supports chapter markers in a very standardized way, with plenty of tool support for folks who want to create them.
So, which do you want more? MP3? Or chapters?