SRT (Secure Reliable Transport)
SRT (Secure Reliable Transport) is an open-source protocol for sending live video over unpredictable networks like the public internet with low delay. It runs on UDP and resends lost packets quickly, within a time window the sender sets. SRT also supports AES encryption. Created by Haivision, it is widely used as a modern alternative to RTMP for contribution (sending feeds from the field to the studio or cloud).
Why it matters
Sending live feeds from stadiums or remote sites used to mean satellite trucks or dedicated fiber. SRT carries broadcast-quality video over the ordinary internet, with encryption, which cuts contribution costs. It also recovers from packet loss that would make an RTMP stream stall or drop. For a sports producer, that means remote feeds from venues with patchy connections can go straight into FastPix over SRT, with no gateway to convert them first.
How it works
- The sender and receiver open a UDP connection and agree on a latency window, such as a few hundred milliseconds.
- Video packets are numbered and sent continuously, optionally encrypted with AES.
- The receiver reports missing packets and the sender resends them while they are still useful.
- Packets that cannot arrive within the window are skipped, so the stream keeps moving instead of freezing.
SRT vs RTMP: which should I use?
Use SRT when the network is unreliable or long distance, and RTMP or RTMPS when simplicity matters most. SRT handles packet loss and jitter better because it resends lost packets within a time window over UDP. RTMP runs on TCP and can stall on lossy links. Most professional encoders now support both.
What latency setting should I use for SRT?
A common starting point is about three to four times the round trip time between sender and receiver. A short, clean connection may work with a few hundred milliseconds. Long or lossy links need a larger window so lost packets have time to be resent. Set it too low and the stream shows dropouts; set it too high and delay grows.
Where it's used
Broadcasters covering live sports and multi-site events use SRT to send stable, encrypted feeds from stadiums and remote locations over ordinary internet instead of expensive satellite links.
Where it usually goes wrong, and how FastPix handles it
Remote feeds over public internet often suffer packet loss and jitter, and RTMP over TCP stalls when that happens, so viewers see freezes even when the venue connection is only briefly unstable.
FastPix accepts SRT ingest alongside RTMPS for live streams. Live streams are delivered as LL-HLS, and stream health stats are available while the stream runs. Your team can spot a struggling venue connection during the event, while there is still time to fix it.
By the numbers
- Haivision and Wowza released SRT as open source and formed the SRT Alliance on April 24, 2017, at NAB in Las Vegas. (Haivision press release: Haivision and Wowza form SRT Alliance)
