Introduction to Three Modes of SRT Protocol ( listener, caller, rendezvous )

SRT is the abbreviation for Secure Reliable Transport. This video transmission protocol can be broadcast live on challenging networks.

SRT is an open source low latency video transmission protocol. It has three characteristics : safety, reliability and low delay. In terms of security, SRT supports AES encryption to ensure end-to-end video transmission security. In terms of reliability, SRT guarantees transmission stability through Forward Correction ( FEC ). In terms of low latency, SRT is based on the improved UDT protocol, which solves the problem of high transmission delay of UDT protocol and the complex transmission timing problem of UDP network communication. It can support real-time transmission of high throughput files and ultra-definition video.

Previously, RTMP was the standard for live Internet video. But RTMP protocol has not been updated for a long time, the standard was abandoned after the last update in 2012. RTMP standard does not support new Codecs such as HEVC or AV1. This is why VLC and other common playback can not play H265 RTMP stream. Now SRT alliance has more than 250 enterprises and organizations, supported by VLC, GSTREAMER, FFMPEG, OBS, VIMX and so on. In the foreseeable future, SRT will replace RTMP.

Three Modes of SRT Protocol ( listener, caller, rendezvous )

In order to establish communication flow, SRT adopts a handshake mechanism, in which each device identifies itself as caller or listener. In some cases, two devices can negotiate SRT sessions in the so-called rendezvous mode at the same time

Caller:

Set the source or target device as the initiator of SRT stream session.

The caller device must know the IP address of the listener and the port number of its listener

Listener:

Set the device to wait for the request to start the SRT stream session.

The listener device just needs to know that it should listen to the SRT stream on a specific port

Rendezvous:

Allows two devices to start SRT sessions on the same port.

Both the source and target must be the rendezvous mode.