Speex

Description
Speex is an open-source audio compression format designed for speech. While the Speex codec and source is still available, it has been obsoleted by the Opus codec.

Speex could be distributed as a single stream (where it normally was given .spx extension in the event being saved to disk), and inside an Ogg container.

Information

 * The Speex Codec Manual Version 1.2 Beta 3
 * Speex Reference Manual 1.2-beta2
 * RFC 5574 - RTP Payload Format for the Speex Codec
 * Speex source

Software
The latest source and binary releases of Speex are available here.

Software supporting Speex can be found here.

Links

 * Speex samples (decoded back to WAV format)
 * A sample .spx file can be found here