Audio File Formats: AAC Follow-up
I want to provide a follow-up to Webmonkey’s audio file format article that ran on Wired News today as part of the “Audiophiles Unite” special report. Just a few notes about AAC files and the various flavors that they come in.
People have been asking me what the differences are between .mp4, .m4a, and .m4p files. They are all AACs, but the spec allows for the file extensions of the AACs to indicate specific information about the type of sound file it is, what kind of playback functionality the file requires, and whether or not it has a DRM scheme attached.
First of all, AAC is MPEG-4 audio. They are one and the same. Also, AAC is not just an Apple thing. It’s a standard audio compression format that any company willing to pay the licensing can incorporate into their product.
Here are the different types:
- .m4a Standard AAC audio. M4a is short for MPEG-4 Audio. M4a files will play in any player that supports AAC playback
- .mp4 Also standard AAC audio. It’s short for MPEG-4 Audio, the MP4 extension is just a way to let people know that these files are the “next generation” after MP3 (Take that for what it’s worth). MP4 files will play in any player that supports AAC playback.
- .m4p Currently, you will only find m4p files in the iTunes Music Store. M4ps contain the FairPlay digital rights management data adopted by Apple. M4p files can only be played in iTunes, on an iPod, or on the ROKR mobile phone. M4p is short for MPEG-4 Audio (protected).
- .m4b This is an audiobook format. An iPod will recognize an m4b file as an audiobook, and the player will bookmark where you left off. You can resume listening at the specific point where you stopped, and you can play the file back at different speeds. If you record spoken word performances or interviews (and if you have an Apple), you can create m4b files with this script to harness the bookmarking feature. M4b files aren’t exclusively used for audiobooks, but the format was created to offer the functionality that makes listening to 2-hour long audio files much easier. Also, M4b files are excluded when your player is in shuffle mode.
The important thing to note is that all of these files are AACs, regardless of their extension. It’s the same codec being used for all of them. Hope that clears everything up.
Thanks to Kevin Edwards for the script link and for supplying some vital information!
