Hi,
Unfortunately we can't know that untill we try to play the file and DRM kicks in notifying that file playback is not authorized.

Re M4B: I never new that, I am glad I do not buy from iTunes as then you can mainly only play those tracks in iTunes now that QuickTime Pro do not exist :( THX for pointing that out.

Correction, .m4b [i]can[/i] be encrypted. If you buy e.g. an audiobook from iTunes, it is an encrypted .m4b.
My point is, the formats have different capabilities (can/cannot be encrypted) and thus it might be useful to be able to treat them differently.

Hi,
Only M4P are encrypted, M4B are AudioBooks and I can play them without problems. Rename M4A to M4B and you will see.

Also M4P are playable if PC is Authorized to be able to play M4P (which from our knowledge Apple removed from iTunes when QuickTime Pro got obsolete).

In the File types dialog box accessible from the Add/Rescan Folders window, .m4a and .aac are listed together with .m4p and .m4b. The second two are encrypted, the first two are not. I want to exclude files that are of a type that MediaMonkey cannot play (without special plugins, if you're lucky) entirely from my library, while not excluding e.g. .aac files. Therefore it would be better to have two entries, e.g:
[list]
[*] Unencrypted AAC (.m4a, .aac)
[*] Encrypted AAC (.m4p, .m4b)
[/list]