oRTP - a Real-time Transport Protocol stack under LGPL.

Features:

 o Written in C, based on glib for unix and windows portability. 
 o Implement the RFC1889 (RTP) with a easy to use API with high and low
   level access.
 o Includes support for multiples profiles, AV profile (RFC1890) being the
   one by default.
 o Includes a packet scheduler for synchronizing rtp recv and send. Scheduling
   is optionnal, rtp sessions can remain not scheduled.
 o Implements blocking and non blocking IO for RTP sessions.
 o Supports mutiplexing IO, so that hundreds of RTP sessions can be managed by
   a single thread.
 o Supports part of RFC2833 for telephone events over RTP.
 o The API is well documented using gtk-doc.
 o Licensed under the Lesser Gnu Public License.

WWW: http://www.linphone.org/ortp/