AAC

AAC (Advanced Audio Coding) is part of the MPEG-2 and MPEG-4 audio specification and is promoted as the successor to MP3 for audio coding at medium to high bitrates. It is the audio format used by the iTunes Music Store and can be played on iPods.

File Extensions

AAC has a number of common file extensions. Unlike some other media formats, there are differences between the file depending on the extension so you cannot rename from one extension to another.

.aac

Usually a raw AAC bitstream. Early AAC encoders often produced files like this. Internet broadcasts are also often AAC bitstreams. To play files like this it is usually the best to wrap an mp4/m4a container around the AAC files as most media players do not like raw AAC data.

.mp4/.m4a

AAC wrapped in an MP4 container. This is how most new AAC encoders produce files. The MP4 container can contain other audio and video formats as well as AAC, so a .mp4 file does not always indicate the presence of AAC (e.g. Apple Lossless is also put in an MP4 container).

In this case there is no difference between the extension (i.e. you can rename .m4a to .mp4 and vice-a-versa).

.m4p

Apple's proprietary copy protected MP4 audio files. No one should be posting these on TMB under any circumstances.

Playback

Software

The following media players will playback AAC files:

• foobar2000
• Winamp
• iTunes
• VLC
• Media Player Classic

Hardware

• iPod

Encoding

Although in theory AAC should outperform MP3 at the same bitrate, early AAC encoders were of a poor quality and would be easily beaten by a decent MP3 encoder like LAME at nearly all bitrates. Below is a list of software with high quality AAC encoders:

• iTunes
• Nero 7