本人开源项目sip2rtsp：
https://github.com/larkguo/sip2rtsp
sip2rtsp is a high-performance software gateway from sip/ims protocol(RFC 3261) to rtsp protocol(RFC 2326). [SIP client1]--> [SIP client2]--> [(network1) SIP2RTSP (network2)] -->[RTSP/RTP stream] ... [SIP clientN]-->
原文：http://larkguo.blog.51cto.com/2422955/1872139