About SPX Files
Speex Audio
Speex is an open-source audio compression format specifically designed for speech encoding. It uses Code-Excited Linear Prediction (CELP) and supports narrowband, wideband, and ultra-wideband modes for different speech quality requirements.
Family
Audio Files
Extension
.spx
MIME Type
audio/x-speex
Can Use As
HOW SPX
CAME TO BE.
Speex was a Xiph.Org codec designed specifically for voice. Jean-Marc Valin released the first version in 2003 as an open-source, patent-free alternative to proprietary voice codecs (GSM, G.729) that dominated VoIP at the time. Speex offered three modes — narrowband, wideband, ultra-wideband — covering 8 kHz to 32 kHz sample rates, all tuned for human speech rather than music.
For a few years Speex was the default VoIP codec in open-source telephony. Asterisk, Ekiga, Linphone, Mumble, and several Nintendo DS game cartridges used it. Then Jean-Marc Valin himself designed Opus (2012) to obsolete Speex — a single codec that handles voice and music better than Speex and Vorbis combined. Xiph.Org officially deprecated Speex in 2012 in favor of Opus. .spx files still exist in legacy VoIP recordings.
CURIOSITIES &
TRIVIA.
Speex's own creator, Jean-Marc Valin, later designed Opus specifically to replace it.
Xiph.Org officially deprecated Speex in 2012 — a rare case of a project retiring its own creation.
Nintendo DS games used Speex for voice and sound effects in titles like Brain Age and Nintendogs.
Mumble voice chat defaulted to Speex before switching to Opus in 2011.
Speex supports three sample rates: narrowband 8 kHz (telephony), wideband 16 kHz (high-quality voice), ultra-wideband 32 kHz.
STRENGTHS &
LIMITATIONS.
Strengths
- Patent-free voice codec.
- Three sample-rate modes for voice.
- Low CPU decode.
Limitations
- Deprecated in favor of Opus.
- No music support.
- Rarely used in new projects.
Typical Sizes & Weights
1 min voice (wideband 24 kbps)
~180 KB
Technical Specifications
- MIME type
- audio/speex
- Extension
- .spx
- Container
- Ogg
- Modes
- Narrowband/Wideband/Ultra-wideband
- Successor
- Opus
CONVERT FROM
SPX
Common Use Cases
Voice over IP, speech encoding, podcast recording, voice chat
Related Formats
Popular comparisons
SPX vs MP3
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SPX vs FLAC
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SPX vs AAC
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SPX vs OGG
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Popular SPX conversions
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Frequently Asked Questions about SPX
Frequently Asked Questions
SPX (Speex Audio) is an audio file format used to store sound recordings — music, voice, podcasts, sound effects. The format defines how the audio samples are compressed (or stored raw), what bitrates are supported, and how metadata such as title, artist, album, and cover art is embedded. It is part of the audio files family.
VLC, foobar2000, and the default media players on Windows and macOS handle SPX natively. On mobile, iOS Music and Android media apps vary in their support — popular formats work everywhere; niche ones may need a dedicated app. If playback fails on a device, converting to MP3 or AAC usually solves it.
Upload the SPX to KaijuConverter and pick MP3, WAV, FLAC, AAC, OGG, or any other target. Our FFmpeg pipeline decodes the audio and re-encodes to the target format at sensible default bitrates (VBR ~190 kbps for music, 96 kbps for speech). Metadata and cover art travel with the audio where both formats support them.
SPX can be lossy or lossless depending on the specific variant. Lossy variants (smaller files) discard some audio detail during compression in ways tuned to be inaudible; lossless variants preserve every sample exactly but produce larger files. For distribution, lossy at high bitrate is standard; for archival, lossless wins.