SPX file format: what it is and how to use it

Speex is the open speech codec designed for low-bitrate voice, the VoIP-era Xiph codec that Opus later replaced. Learn when to use it and what to choose instead.

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What is a SPX file?

An .spx file is speech audio compressed with Speex, the Xiph.Org codec built specifically for voice: patent-free, tuned for low bitrates (2–44 kbps), with features like VBR, voice-activity detection and stereo support inside an Ogg container. It powered early VoIP and podcast apps until Opus, its own successor, made it largely historical.

When should you use SPX?

  • Reading legacy voice archives: old recordings, VoIP captures and audiobook projects.
  • Extreme low-bitrate voice: where it still appears in embedded systems.
  • Open codec pipelines: the Xiph patent-free ecosystem it belongs to.

When is another format a better fit?

For anything new, Opus is the direct successor: better quality at every bitrate and the standard for real-time voice. For playback compatibility MP3; for music anything but Speex, which is speech-tuned by design.

The short version: SPX is the open speech codec that Opus replaced. Convert it forward, and keep it readable.

How to open a SPX file

On Windows

Double-click the file, or open it with Foobar2000.

On macOS

VLC opens SPX files on macOS.

In your browser

Open SPX files right in a browser tab or with the dexrr viewer. No install, no upload.

Also opens in

  • VLC
  • Foobar2000
  • mpv

View or convert SPX files

A quick preview or a new format. No install, no upload.

View SPX files Preview and inspect SPX files Convert to SPX Turn files into SPX SPX to OPUS Opus audio SPX to VORBIS Vorbis audio codec

SPX technical details

Full name
Speex audio
Extensions
.spx
MIME type
audio/speex, audio/x-speex, audio/ogg
Magic bytes
4F 67 67 53 (OggS) + Speex
Compression
Lossy
Developer
Xiph.Org Foundation
Specification
www.speex.org

SPX questions, answered

How do I open a .spx file?

VLC, foobar2000, FFmpeg tools and Xiph-era players decode it; modern OS players usually do not. dexrr plays and converts spx files in your browser.

Can I convert SPX files online?

Yes, dexrr converts speex locally in your browser: Speex to MP3 for playback or Speex to WAV for editing.

Is Speex better than Opus?

No. Opus is its own successor, better at every bitrate for both speech and music. Speex survives only in old files.

Why does my .spx sound robotic?

It was tuned for intelligible speech at very low bitrates, not fidelity. That is the codec working as designed, not corruption.

Is the SPX format outdated?

Yes, effectively replaced by Opus; it persists in legacy recordings and embedded voice systems.