What is the SPX file format?
An .spx file is an Ogg Speex audio file: an .ogg container encapsulating a Speex-encoded speech stream. Speex is an open-source CELP (Code Excited Linear Prediction) codec developed by the Xiph.Org Foundation, designed exclusively for voice and speech compression rather than music.
The Speex codec supports three operating modes: narrowband (8 kHz, optimized for telephone-quality voice), wideband (16 kHz), and ultra-wideband (32 kHz). Bitrates range from approximately 2 to 44 kbps, and variable bitrate (VBR) mode is supported. The Ogg container adds per-page CRC32 integrity checks and embeds Vorbis comment tags (artist, title, etc.) for metadata.
.spx files were widely used in VoIP applications and internet telephony during the 2000s - Ekiga, Mumble, and TeamSpeak used Speex at various points. The format is still encountered in archived voice recordings and legacy teleconferencing systems.
In 2012, the Xiph.Org Foundation released .opus, which outperforms Speex in every measurable category: better quality at lower bitrates, support for stereo and multichannel audio, and lower algorithmic delay. Xiph formally deprecated Speex in favour of Opus for all new deployments. For playback, VLC and Foobar2000 both support .spx natively.
Security & safety
RISK: LOWPure audio container; no known exploit vectors specific to Speex/Ogg. Standard caution: don't open files from untrusted sources in unpatched players (historical libspeex and libogg CVEs exist but are patched in all current versions).
Format details
in a nutshell- Speex raw bitstream (headerless) - Rare; some tools emit raw Speex frames without an Ogg container using the same .spx extension.
Programs that open SPX files
Windows3 apps
macOS1 app
Linux2 apps
Android1 app
Technical details
deep spec| Container format | Ogg bitstream (magic bytes 4F 67 67 53 - 'OggS' at offset 0) |
| Audio codec | Speex CELP (Code Excited Linear Prediction) - lossy, optimized for voice and speech |
| Codec identification | 'Speex ' (8-byte string with 3 trailing spaces) at offset 28 of the first Ogg page header |
| Supported sample rates | 8 kHz (narrowband), 16 kHz (wideband), 32 kHz (ultra-wideband); all three modes can coexist in the same stream |
| Bitrate range | Approximately 2-44 kbps; variable bitrate (VBR) mode supported |
| Encoding | Binary; Ogg framing and Speex headers are little-endian |
| Integrity checking | Ogg page-level CRC32 (4 bytes at offset 22 of each Ogg page header) |
| Header structure | Speex fixed header (80 bytes), followed by Vorbis comment metadata header, then audio data pages |
| Metadata tags | Vorbis comment format: TITLE, ARTIST, COMMENT fields stored in the second logical bitstream page |
| Typical file size | 20 KB - 5 MB (voice recordings at 2-44 kbps) |
| Primary use case | VoIP recordings, internet telephony, archived speech; not designed for music |
| Successor codec | Opus (RFC 6716, 2012); Xiph.Org formally deprecated Speex in favour of Opus for all new deployments |
| Released | 2002 (Speex 1.0 beta 1) |
| Latest version | Speex 1.2.1 (2022); format spec stable since 1.0 |
| Open standard | Yes · royalty-free |
| Specification | speex.org |
SPX conversions
Community Q&A
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