Audio File Format Specifications

File Description: AU or NeXT/Sun sound file
File Extension: Commonly .au, sometimes .snd
File Byte Order: Big-endian

Prof. Peter Kabal, MMSP Lab, ECE, McGill University: Last update: 2017-01-20

AU File Specifications

The AU file specifications came from NeXT Computer and Sun. The AU file format uses as simple extensible header, followed by data. The minimum header length is 28 bytes.

Offset Length Type Contents
0 4 character File magic .snd
4 4 unsigned integer Offset to start of data
8 4 unsigned integer Number of bytes of data
12 4 unsigned integer Data format code
16 4 unsigned integer Sampling rate
20 4 unsigned integer Number of channels
24 - character Optional text information (minimum 4 bytes)

Data Types

The data in AU files can be of several different types. The data is stored in little-endian byte order. Common format codes are listed in the following table. See Audio File Format FAQ for additional codes.

Format Code PreProcessor Symbol Data Type
1 SND_FORMAT_MULAW_8 8-bit ITU-T G.711 -law
2 SND_FORMAT_LINEAR_8 8-bit integer
3 SND_FORMAT_LINEAR_16 16-bit integer
4 SND_FORMAT_LINEAR_24 24-bit integer
5 SND_FORMAT_LINEAR_32 32-bit integer
6 SND_FORMAT_FLOAT 32-bit IEEE float
27 SND_FORMAT_ALAW_8 8-bit ITU-T G.711 A-law

An implementation for reading and writing AU files is available as part of the Audio File Library

AU Sample Files