I don't know if this is a bug with the new M4A code in Mp3Tag or just some quirk of iTunes, but if I edit any field of a M4A file with Mp3Tag (v2.32s) and then try to add the file to iTunes, iTunes fails to see any header fields (even fields that previously existed/displayed in the file). I've tried this with iTunes 5.0 on both OS X 10.3 and XP, and iTunes 4.7 on Win 2000.
Note that all field M4A fields, edited or not, are recognized just fine by WinAmp 5, by dbPowerAmp Tag Editor, by Tag&Rename, etc. It seems to be only iTunes that can't see the tag info. Also note that the edited files play musically just fine on iTunes -- it's just that the tag info is not displayed.
My testing procedure is to take an original M4A file where all tag fields display just fine in iTunes. I make a copy of this file, and then add a comment using Mp3Tag(v2.32s) and save. I copy both files to an empty iTunes directory, delete the iTunes DB ('iTunes Library.xml', 'iTunes Library' files), start iTunes which show an empty library, select "Add Folder..." under "File" pointing to the directory contain the orginal and edit file. When loaded, the orginal file shows all tag fields; the edit file shows no tag fields. As I said, both files will play properly.
I'm going to email these sample files to:
I hope you can help me solve this problem quickly. These files are actually my girlfriend's music library. Her iTunes library was a mess (missing track ids, genres, bad titles, etc). I bragged that I could clean up her library using Mp3Tag (on my XP machine). When I rebuilt/re-added all her newly edited files (to create new XML library file) into her iTunes (OS X 10.4), this problem popped up with the M4A files (MP3 display flawlessly). I can't convince her to move to XP and WinAmp (which is what I use for my music library and have no problems with). Now she's so mad that I'm afraid I'm going to have to sleep alone on the couch until I can get this problem fixed for her.
BTW, don't know if MPEG settings affect the M4A tag code, but I've got all checked for "Read", only ID3v1 and ID3v2 checked for "Write" (all others unchecked including new ISO-8859-1 option).
If you need any more info, please let me know.