rtpengine is a media relay, WebRTC bridge, call recorder, media transcoder, and media player. It can relay and manipulate media in real-time by forwarding packets through a kernel module. It supports features like SDP profile transforming, ICE negotiation, DTLS-SRTP encryption, packet recording, transcoding between codecs, and injecting audio streams into calls from files or databases. rtpengine integrates with Kamailio through modules and configuration to manipulate media on SIP calls.

1. rtpengine
Media Relaying and Beyond
Andreas Granig <agranig@sipwise.com>

2. WHAT IS IT?
rtpengine
Media Relay WebRTC Bridge Call Recorder Media Transcoder Media Player

3. MEDIA RELAY
rtpengine
● Kernel based forwarding
● Network bridging (IPv4, IPv6)
● IP load balancing (more ports)
● State syncing (Redis)

4. MEDIA RELAY
rtpengine
rtpengine.so module in Kamailio
rtpengine daemon
xt_RTPENGINE kernel module
rtpengine
Kamailio
SIP
RTP
original SDP + meta info modified SDP + meta info

5. MEDIA RELAY
rtpengine
route {
...
rtpengine_manage();
...
}
rtpengine
--interface=ext/1.2.3.4
--listen-ng=127.0.0.1:12221
Kamailio Config rtpengine

6. WEBRTC BRIDGE
rtpengine
● SDP profile transforming
○ RTP/AVP ⬌ RTP/SAVPF
● In-Kernel DTLS-SRTP crypto
● ICE negotiation
● RTCP multiplexing

7. WEBRTC BRIDGE
rtpengine
rtpengine
Kamailio
SIP
RTP
original SDP + meta info
modified SDP:
● changed profile
● added ICE candidates
● RTCP mux
DTLS-RTP

8. WEBRTC BRIDGE
rtpengine
route {
rtpengine_offer(“RTP/SAVPF ICE=force”);
}
reply_route {
rtpengine_answer(“RTP/AVP ICE=remove
rtcp-mux-demux”);
}
rtpengine
--interface=ext/1.2.3.4
--listen-ng=127.0.0.1:12221
Kamailio Config rtpengine

9. CALL RECORDER
rtpengine
● Started/stopped before or during call
● Packet forking to /proc in real-time
● Storing streams as WAV/MP3 on NFS
● Storing meta-data in MySQL

10. CALL RECORDER
rtpengine
rtpengine
Kamailio
SIP
RTP
original SDP + meta info
recorder
metainfo /var/spool/recordings/
/proc/rtpengine/0/calls/
out.wav /nfs/recordings/Packet Queue
modified SDP + meta info

11. CALL RECORDER
rtpengine
route {
rtpengine_manage(“record-call
metadata=uuid:$var(aid)|
uuid:$var(bid)”);
}
rtpengine
--interface=ext/1.2.3.4
--listen-ng=127.0.0.1:12221
--recording-method=proc
--recording-dir=/var/spool/rtpengine
Kamailio Config rtpengine

12. MEDIA TRANSCODER
rtpengine
● Transcoding audio streams
● Supporting Opus, G711, G729, G722,
speex, … (see rtpengine --codecs)
● Operating in user-space
● Allowing last-resort and forced mode

13. MEDIA TRANSCODER
rtpengine
rtpengine
Kamailio
SIP
RTP G711
original SDP + meta info
modified SDP:
● filter unwanted codecs
● add additional codecs
RTP Opus

14. MEDIA TRANSCODER
rtpengine
route {
rtpengine_manage(“mask-all
transcode-opus”);
}
rtpengine
--interface=ext/1.2.3.4
--listen-ng=127.0.0.1:12221
Kamailio Config rtpengine

15. MEDIA PLAYER
rtpengine
● Injecting audio into streams
● Playing from local files or MySQL blobs

16. MEDIA PLAYER
rtpengine
rtpengine
Kamailio
SIP
RTP
● call-id of existing
call
● from-tag/address
● file/db-id
● calculated duration
in.wav

17. MEDIA PLAYER
rtpengine
event_route[xhttp:request] {
play_media(“call-id=$var(callid)
from-tag=$var(fromtag)
file=/path/to/hello.mp3”);
}
rtpengine
--interface=ext/1.2.3.4
--listen-ng=127.0.0.1:12221
Kamailio Config rtpengine

18. MORE FEATURES
rtpengine
● DTMF logging
● Media and DTMF blocking/unblocking
○ block/unblock_dtmf(...)
○ block/unblock_media(...)
● Stream forwarding to 3rd party via TLS
(for example to speech recognition
engine)
○ start/stop_forwarding(...)
● MOS reporting via AVPs
○ mos_xxx_pv mod-param

19. THANK YOU
Questions?