iLBC (internet Low Bitrate Codec) is a FREE speech codec suitable for robust
voice communication over IP. The codec is designed for narrow band speech and
results in a payload bit rate of 13.33 kbit/s with an encoding frame length
of 30 ms and 15.20 kbps with an encoding length of 20 ms. The iLBC codec
enables graceful speech quality degradation in the case of lost frames,
which occurs in connection with lost or delayed IP packets.

WWW: http://github.com/dekkers/libilbc