This format extension is one of the Speex Audio formats. It is an open-source codec developed by Xiph.Org. Used for creating voice messages and transmitting voice over packet-based networks with a low level of security. It is an audio file with recorded voice messages that are packaged in an OGG file. Only certain media players can open it.

AU format for reliable data storage

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.