What is the SND file format?
The .snd format is a binary audio container developed by NeXT Computer and Sun Microsystems, introduced in 1988 with NeXTSTEP 1.0. It shares its binary format entirely with .au files - the two extensions are interchangeable, both opening with the magic bytes .snd (hex 2E 73 6E 64) at offset zero.
The file begins with a compact 24-byte fixed header storing the magic constant, data offset, data size, encoding type, sample rate, and channel count. An optional null-terminated annotation block follows, padded to a multiple of 8 bytes, then the raw audio data. All header fields use big-endian (network) byte order.
The encoding field in the header identifies the audio format: 1 = µ-law 8-bit (telephony), 2-5 = linear PCM in 8, 16, 24, or 32-bit, 6-7 = IEEE float 32 or 64-bit, and 23-25 = G.721/G.723 ADPCM. Uncompressed linear 16-bit PCM is most common.
NeXTSTEP used the .snd extension for system sounds; Sun workstations and early internet audio streams favored .au for the identical format. When Apple acquired NeXT in 1996, macOS inherited legacy .snd support. The format defined the audio/basic MIME type, which became the first standardized internet audio type registered with IANA.
New .snd files are rarely created today. WAV replaced it on Windows and AIFF on macOS. Modern players including VLC and Audacity still open .snd files without issue.
Security & safety
RISK: LOW.snd files are simple audio containers with no executable code. Risk is low. Files downloaded from unknown sources should be scanned, but this format carries no known exploit history.
Format details
in a nutshell- Macintosh FSSD/8SVX Sound Resource - Classic Mac OS system sounds were stored as 'snd ' resources inside resource forks, sometimes exported as .snd files - structurally different from the NeXT format.
- Amiga/SoundBlaster raw PCM - Some DOS/Amiga tools saved headerless raw PCM with .snd extension; no header, format identified only by convention.
Programs that open SND files
Windows4 apps
Windows Media Player
Built-in Double-click the .snd file; WMP may play mu-law and PCM variants with DirectShow filters. 
VLC media player
Open-source File → Open File, select the .snd file. VLC detects the AU/SND format automatically. 
Audacity
Open-source File → Open, select .snd file. Allows editing, conversion, and export to other formats. 
macOS2 apps
QuickTime Player
Built-in Double-click .snd; QuickTime has native AU/SND support inherited from NeXT. 
Linux2 apps
Technical details
deep spec| Magic bytes | `2E 73 6E 64` (ASCII `.snd`) at offset 0 - identical to `.au` |
| MIME type | `audio/basic` (primary); also `audio/x-au`, `audio/snd` |
| Byte order | Big-endian (network byte order) for all header fields |
| Fixed header size | 24 bytes: magic, data offset, data size, encoding type, sample rate, channel count |
| Annotation block | Null-terminated comment appended after the 24-byte header, padded to an 8-byte boundary |
| Encoding field values | `1`=µ-law 8-bit, `2`=PCM 8-bit, `3`=PCM 16-bit, `4`=PCM 24-bit, `5`=PCM 32-bit, `6`=float 32-bit, `7`=float 64-bit, `23`=G.721 ADPCM |
| Compression | Typically none (PCM); also supports µ-law, A-law, and G.721/G.723 ADPCM per encoding field |
| Sample rate | Any integer Hz stored in header; common values: 8000 Hz (telephony), 22050 Hz, 44100 Hz |
| Channel count | Stored in header; mono (1) and stereo (2) most common; no hard upper limit defined |
| Typical file size | 10 KB - 50 MB; system sounds typically 10-500 KB |
| Interchangeable extension | `.au` - same binary format, same magic bytes; NeXT used `.snd`, Sun workstations used `.au` |
| Associated operating systems | NeXTSTEP, OPENSTEP, Solaris/SunOS, macOS (legacy), Linux |
| Internet audio heritage | Defined the `audio/basic` MIME type - the first standardized internet audio type registered with IANA (RFC 2045) |
| Integrity / encryption | None - no checksum field, no encryption support |
| Released | 1988 (NeXTSTEP 1.0) |
| Latest version | No formal versioning; format stable since early 1990s |
| Open standard | Yes · royalty-free |
| Specification | pubs.opengroup.org |
SND conversions
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