AAC

Also known as Advanced Audio Coding, is the MPEG-4 audio standard that supports, amongst other things, multi-channel audio (as in more than two).

It is not, as a gazillion idiots like to write, “‘s proprietary format”. It’s an industry standard, supported by pretty much every modern mobile phone and most “ players”. What is exclusive to the (and the abomination known as ) is ‘s FairPlay, but ripping your own audio into high-grade does not encumber files in any way.

Note: More info here, with mentions of Fairplay.

(As reported in MacRumors for the implementation - should be mostly the same for other -related DRM policies):

How it Works

Surprisingly few details about the implementation of the AAC have been revealed. The following represents a list of restrictions and capabilities for consumers as known at this time -

  • Protected files have the extension: .m4p – ripped files are .m4a
  • Unlimited CD Burning of Protected s
  • Only the and ‘s , and it seems -based apps currently allow playing of these Protected ‘s.
  • Up to three computers (at one time) can be authorized to play Puchased ‘s. Deauthorizing your computer and reauthorzing new computers is relatively simple (Note: uses the “Authorize/Deauthorize Computer” menu, no details as to the transport mechanism and PKI employed)
  • Playlists containing any Protected ‘s can only be burned 10 times. You must change the list manually before you can burn again.
  • Burning a Protected to a CD strips all encoding and DRM. That CD can then be used as any CD song is used. The quality of the song on the CD is identical to the version. However, then ripping the song into or will result in loss of some quality. While ripping a song into any lossy compression format will result in loss of quality – recompressing these previously compressed songs may exaggerate the quality loss. Your results will vary depending on the exact piece of audio. Anecdotal evidence suggests re-ripping into yields better quality than re-ripping into .
  • Transcoding from Protected to /AIFF from is prohibited by .
  • If you’re listening to a shared library or playlist, skips any purchased music in the list (if the computer is not authorized to play the music). To listen to a purchased song in a shared library or playlist, you need to double-click the song. If your computer is not authorized to play songs purchased by the person who is sharing the song, you’ll need to enter that person’s Apple Account ID and password to hear the song.
  • According to : will only play files that are created by or downloaded from the Music Store. “Other files that you find on the Internet or elsewhere will not play in .” However, Anecdotal evidence does not support this. Users have reported being able to play files encoded outside of .
  • s you rip from CD yourself (via ) have no restrictions.
  • Authorization/Deauthorization appears to be based on a central server model… as claims that “Initializing the drive will not deauthorize the computer. If you will be initializing the drive, deauthorize the computer first, then initialize the drive.”

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