AAC stands for Advanced Audio Coding and it is an audio format similar to MP3 but with performance optimizations.
Compared to MP3, AAC format has improved encoding efficiency, simpler filterbank and optimized handling of frequencies above 16 kHz, therefore users will need to find a specialized software solution for correctly creating AAC files.
Users prefer AAC over MP3 because it sounds better at similar bit rates, therefore they typically create AAC files by converting their files to this format.
Additionally, users will be able to modify the source files' bit rates and audio channel before generating AAC tracks.