I believe AAC is also known as mp4. It is an option in the Macintosh software iTunes, when I compress a wav or aiff file. I used that format a few times, but gave it up when I could not play them in Windows Media Player.
The only time I had to look up an audio codec was when I wanted to create mp3's in Audacity (free digital sound processing software, available for Mac and Windows).
The Audacity instructions told me I had to install a translator called 'LAME'. I found a website to download it from. I put it in the Audacity folder. Then Audacity could find it and use it to create mp3's.
ITunes and Audacity allow me to set mp3 bit rate, mono or stereo, etc.
I believe Windows has its proprietary codec for creating wma files, going back earlier than mp3's.