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

Features:

 * Written in C
 * Implement the RFC3550 (RTP) with a easy to use API with high and low level
   access.
 * Includes support for multiples profiles, AV profile (RFC1890) being the one
   by default.
 * Includes a packet scheduler for synchronizing rtp recv and send. Scheduling
   is optionnal, rtp sessions can remain not scheduled.
 * Implements blocking and non blocking IO for RTP sessions.
 * Supports mutiplexing IO, so that hundreds of RTP sessions can be managed by
   a single thread.
 * Supports part of RFC2833 for telephone events over RTP.
 * The API is well documented using gtk-doc.
 * Licensed under the Lesser Gnu Public License.
 * RTCP messages sent periodically since 0.7.0 (compound packet including
   sender report or receiver report + SDES)

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