AAC

AAC (advanced audio coding) is a lossy coding standard (codec) for audio files and was developed as a successor to MP3.

Compared to MP3 it has a better sound quality according to the English Wikipedia page.

In contrast to other formats AAC is proprietary software and not free/open. As a consequence of this licensing scheme, vendors have to pay a licensing fee in order to implement the format in their products.

It was developed in cooperation with various companies, including Sony and Nokia. The typical file extension is .aac, but depending on the container, files with the extensions m4a, mp4, 3gp, m4b, m4p, m4r or m4v may contain this format.

Since AAC compresses lossy, this format should only be used if the files were originally created in this format.

This means a conversion from another format to AAC is not recommended.

Advantages:

- better quality than MP3 under the same conditions

- standardized

Disadvantages:

- lossy compression

- proprietary

https://en.wikipedia.org/wiki/Advanced_Audio_Coding#Standardization