I may have been in error, since I was just posting what I read on another forum.... but I now don't think the actual format is "AAC". The actual file extension that requiem converts the file into is .m4a, and the .m4a can be played in programs such as winamp without trouble.
So the format to look at would probably be .m4a. However, I was able to fill my full name and email in with random bytes, and the file still plays fine. But I am not sure if there is other info that could link me (I wasn't able to see anything readable though).
Edit: It looks like m4a and mp4 are pretty much the same file format. Here is a quote from wikipedia:
[.M4A VS .MP4] wrote:
The existence of two different file extensions for naming audio-only MP4 files has been a source of confusion among users and multimedia playback software. Since MPEG-4 Part 14 is a container format, MPEG-4 files may contain any number of audio, video, and even subtitle streams, making it impossible to determine the type of streams in an MPEG-4 file based on its filename extension alone. In response, Apple Inc. started using and popularizing the .m4a file extension. Software capable of audio/video playback should recognize files with either .m4a or .mp4 file extensions, as would be expected, as there are no file format differences between the two.
.. looks like they use .m4a to determine that it's audio.