These are different container formats that are primarily used to save data compressed with the lossy AAC compression algorithm. Amadeus Pro will downmix multitrack documents it to a mono or stereo file, whichever is more suitable.
Metadata is lost when saving to the AAC ADTS format, but it is preserved when saving to the three other formats.
Note that the AAC ADTS format is not the same as the Mp4 or Apple’s M4a format. These are three different container formats and QuickTime for example will not be able to read AAC ADTS files. On the other hand, the M4a and the Bookmarkable AAC format differ only in the file extension, but are treated differently by iTunes and the iPod.
In most cases, you will probably wish to use the MPEG Audio (.m4a) format as this is the format used by Apple’s iTunes Store.
