The Speex project aims to build an open-source, patent-free voice
codec.  Unlike other codecs like MP3 and Ogg Vorbis, Speex is
specially designed for compressing voice at low bitrates in the
8-32 kbps/channel range.  Possible applications include Voice over
IP (VoIP), internet audio streaming, archiving of speech data (e.g.
voice mail), and audio books.  In some sense, it is meant to be
complementary to the Ogg Vorbis codec.

Homepage:
https://www.speex.org/
