NeXT/Sun Microsystems µ-Law audio file magic bytes (.au)
.au file signature: 2E 73 6E 64 | audio/basic
Category: Audio
NeXT/Sun Microsystems µ-Law audio file is an audio file format developed by NeXT and later supported by Sun Microsystems for storing mu-law encoded sound data. It is used for simple audio playback, archival voice recordings, and legacy Unix audio workflows, especially on older systems and software. The format is largely legacy and poses no special security concerns beyond the usual risks associated with opening untrusted media files.
Magic Bytes
Offset 0
2E 73 6E 64
Sources: Apache Tika, Wikipedia, Gary Kessler
All Known Signatures
3 signature variants are documented for .au files across multiple sources.
| Hex Signature | Offset | Sources |
|---|---|---|
| 2E 73 6E 64 | 0 | Apache Tika, Wikipedia, Gary Kessler |
| 2E 73 6E 64 00 00 00 | 0 | Apache Tika |
| 64 6E 73 2E | 0 | Gary Kessler |
Validation Code
How to validate .au files in Python
def is_au(file_path: str) -> bool:
"""Check if file is a valid AU by magic bytes."""
signature = bytes([0x2E, 0x73, 0x6E, 0x64])
with open(file_path, "rb") as f:
return f.read(4) == signatureHow to validate .au files in Node.js
function isAU(buffer: Buffer): boolean {
const signature = Buffer.from([0x2E, 0x73, 0x6E, 0x64]);
return buffer.subarray(0, 4).equals(signature);
}How to validate .au files in Go
func IsAU(data []byte) bool {
signature := []byte{0x2E, 0x73, 0x6E, 0x64}
if len(data) < 4 {
return false
}
return bytes.Equal(data[:4], signature)
}API Endpoint
/api/v1/au
curl https://filesignature.org/api/v1/au
See the full API documentation for all endpoints and parameters.
Related Formats
Frequently Asked Questions
What is a .au file?
A .au file is a NeXT/Sun Microsystems µ-Law audio file. NeXT/Sun Microsystems µ-Law audio file is an audio file format developed by NeXT and later supported by Sun Microsystems for storing mu-law encoded sound data. It is used for simple audio playback, archival voice recordings, and legacy Unix audio workflows, especially on older systems and software. The format is largely legacy and poses no special security concerns beyond the usual risks associated with opening untrusted media files.
What are the magic bytes for .au files?
The magic bytes for NeXT/Sun Microsystems µ-Law audio file (.au) files are 2E 73 6E 64 at byte offset 0. These bytes identify the file format more reliably than the extension alone.
How do I validate a .au file?
To validate a .au file, read the first bytes of the file and compare them against the known magic bytes (2E 73 6E 64) at offset 0. This is more reliable than checking the file extension alone, as extensions can be renamed.
What is the MIME type for .au files?
The primary MIME type for .au files is audio/basic.
Is it safe to open .au files?
NeXT/Sun Microsystems µ-Law audio file (.au) files are generally safe to open. They are classified as low risk because they primarily contain data rather than executable code. However, always ensure files come from a trusted source.