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
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 |
| 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) |
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 µ-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 |
7 |
SND_FORMAT_DOUBLE |
64-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