AAC

From Anipedia

AAC (Advanced Audio Coding) is Apple's standardized audio file format. It is often in the form of a locked or protected format, as they can be purchased from the iTunes store.

Most animation related software can export their audio tracks to AAC, for those who want to separate their audio and video tracks. Adobe Flash does not support this feature.

Refer to audio conversion for tips on how to convert audio files to AAC.