Why I cannot play M4A audio on iTunes, but I can play it on QuickTime? I have some M4A audio files, that I can't play on iTunes (e.g. double click the file, and then iTunes fired up, the audio added to the library, but the play doesn't start. Tried double clicking on the audio on the library, still doesn't start the player).

But when I open them in QuickTime, QuickTime can play it. Why that happens? And what can I do about it so I can import those files to iTunes? Thanks.
Changing the extension to .mp4 from .m4a worked for me but as a solution sucks since I now have to change it for each file individually. With a large music collection failing the same way this solution with take significant time to implement.