This audio format was developed by Sun Microsystems. It is intended for storing audio files; the file itself consists of three components: the header, the annotation unit, and the audio file itself. What distinguishes this format is the small file size, due to which its sound quality is low. It can be converted into other formats, such as mp3 or MPEG. Although this format is mostly used on personal computers that are powered by operating systems Sun or Unix, AU files can also be opened using other audio players.

opus

Opus (formerly Harmony): an audio codec for lossy compression

This format was created for online broadcasting. Opus is an audio codec for compression used on the Internet in real-time mode. Employed by programs such as Skype and Mozilla. Mostly used in interactive applications. The advantages of Opus are high audio quality and good compression. It works only on devices powered by Windows. Opus files can be converted to similar extensions.