SRT basics (caller / listener / rendezvous)
SRT can operate in three connection modes:
Listener
- The receiver (server side) listens on a UDP port.
- The sender connects as a Caller.
Typical:
- Server:
srt://0.0.0.0:PORT?mode=listener
- Remote:
srt://PUBLIC_IP:PORT?mode=caller
Caller
- The device initiates the connection to a remote Listener.
- Used when the destination has a public IP/port reachable.
Typical:
- Device:
srt://REMOTE_IP:PORT?mode=caller
Rendezvous
- Both endpoints initiate a connection to each other.
- Useful in some NAT scenarios when direct inbound is hard.
Typical:
- Both sides use
mode=rendezvous and the same port mapping rules.
Ports (important)
- One SRT session uses one UDP port.
- If you need many simultaneous SRT streams, you must plan a UDP port range.
- For inbound SRT over the Internet:
- Forward the chosen UDP port(s)/range to the device IP.
- Avoid overlap with other services.
Reliability vs latency (high level)
SRT can handle packet loss/jitter using buffers and retransmission.
Trade-off:
- Larger buffers = more resilience, more latency.
- Smaller buffers = less latency, less tolerance to loss/jitter.