Au file format

Au
Filename extension
.au
.snd
Internet media typeaudio/basic (headerless format)[1]
Type code
  • public.au-audio[2]
  • public.ulaw-audio[3] (headerless variant)
Magic number.snd (newer versions)
Developed bySun Microsystems
Type of formataudio file format, container format
Container forAudio, most often μ-law

The Au file format is a simple audio file format introduced by Sun Microsystems. The format was common on NeXT systems and on early Web pages. Originally it was headerless, being 8-bit μ-law-encoded data at an 8000 Hz sample rate.[1] Hardware from other vendors often used sample rates as high as 8192 Hz, often integer multiples of video clock signal frequencies. Newer files have a header that consists of six unsigned 32-bit words, an optional information chunk which is always of non-zero size, and then the data (in big-endian format).

Although the format now supports many audio encoding formats, it remains associated with the μ-law logarithmic encoding. This encoding was native to the SPARCstation 1 hardware, where SunOS exposed the encoding to application programs through the /dev/audio device file interface. This encoding and interface became a de facto standard for Unix sound.

  1. ^ a b "audio/basic". IANA.org. Retrieved 23 February 2023.
  2. ^ "AVFileTypeSunAU". Apple Developer Documentation. Apple Inc.
  3. ^ "System-Declared Uniform Type Identifiers". Uniform Type Identifiers Reference. Apple Inc.