.spx

What is a .spx file?

Speex is an open-source speech codec now largely replaced by Opus, which offers better quality at lower bitrates.

Safe format
Type Audio
By Xiph.org Foundation (Jean-Marc Valin)
MIME audio/ogg

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What is it

Speex was the open-source speech codec before Opus made it obsolete. Developed by the Xiph.org Foundation (the same people behind Ogg Vorbis and FLAC), it was designed specifically for voice — VoIP calls, voice chat, audiobook recording — at bitrates from 2 to 44 kbps. It was good at its job and royalty-free, which made it popular in open-source VoIP projects.

The format officially reached end-of-life when the Xiph.org Foundation declared Opus as Speex's successor. Opus handles everything Speex did — speech at low bitrates — while also handling music at high bitrates. There's genuinely no technical reason to use Speex for new projects.

You'll encounter SPX files in older VoIP recordings, legacy audiobook archives, and open-source voice applications. VLC plays them. For archival, convert to Opus (direct successor, better quality) or MP3/AAC (universal compatibility). The Speex project's own website recommends using Opus instead.

Technical details
Full Name
Speex Audio
MIME Type
audio/ogg
Developer
Xiph.org Foundation (Jean-Marc Valin)
Magic Bytes
4F 67 67 53
Safety
.spx is a known, safe format. Audio data only. No executable content.
What opens it
VLC
FREE Windows / Mac / Linux
foobar2000
FREE Windows
FAQ
Is Speex still used?
Rarely for new projects. Opus has officially replaced Speex — it offers better quality at the same bitrates for both speech and music. Speex exists mainly in legacy systems.
How do I convert SPX to MP3?
FFmpeg handles it: `ffmpeg -i input.spx -c:a libmp3lame -q:a 4 output.mp3`. The quality won't improve (Speex already discarded detail), but the file will be universally playable.
Related formats