An .au file is the Sun audio format, one of the earliest structured audio files, created for Unix workstations. A minimal header followed by sample data, classically 8 kHz mu-law telephony audio, makes .au about as simple as an audio format can get.
Batch files can each use a different output. Nothing uploads for local conversions.
Working inputs include camera RAW, browser-local audio/video, PDF, CBZ/CBR comics, office documents, ebooks, markup, 3D models, structured text, images, and archives.Sun Microsystems introduced the format for its SPARC workstations in the late 1980s, sharing the underlying design with NeXT's .snd files. It became the web's first common sound format in the Mosaic era and lived on as the only format early Java applets could play.
Audio tools such as Audacity, sox, and ffmpeg open .au readily, and Java's sound APIs still accept it. Consumer players, phones, and browsers dropped meaningful support long ago, so conversion to WAV or MP3 is the practical route.
An optional annotation field in the header can hold a short text string; no formal tag structure exists.
