What Is SRT?
Secure Reliable Transport — the professional standard for live video over the public internet. How it works, why it replaced RTMP and when to use it.
SRT (Secure Reliable Transport) is an open-source video transport protocol designed for sending broadcast-quality live video over unreliable networks — including the public internet, 4G and 5G cellular. Developed by Haivision and released as open source in 2017, it has become the professional standard for live video contribution, replacing RTMP for broadcast-grade streaming workflows.
How SRT Works
Traditional streaming protocols like RTMP use TCP — a connection-oriented protocol that requires every packet to arrive in order. When packets are lost on a congested internet path, TCP stalls waiting for retransmission and the stream freezes, degrades or disconnects.
SRT uses UDP — a faster, connectionless protocol — but adds its own intelligent error correction on top. When a packet is lost, SRT detects the gap and requests a retransmission. The replacement packet arrives within a configurable latency buffer before it is needed for playback. The viewer sees smooth, continuous video. The network disruption is invisible.
This combination — UDP speed with intelligent retransmission — makes SRT streams resilient to the packet loss, jitter and congestion that are unavoidable on public internet connections, cellular networks and long-distance contribution paths.
Key Features of SRT
Automatic Packet Retransmission
Lost packets are detected and re-sent within the latency buffer. Streams survive packet loss that would disconnect an RTMP stream entirely.
AES Encryption Built-In
AES-128 and AES-256 encryption is native to SRT. Both encoder and decoder share a passphrase. No separate encryption layer needed.
Configurable Latency
Set the buffer from 20ms (local network) to several seconds (satellite). Tune for your network conditions — more buffer for worse connections.
Live Stream Statistics
SRT provides real-time RTT, packet loss percentage and retransmission rate. Monitor stream health and detect network problems before they affect viewers.
Open Source & Royalty-Free
SRT is free to implement and use. The SRT Alliance includes 600+ companies. No licensing fees for hardware manufacturers or software developers.
Works Over Any IP Network
Broadband, 4G, 5G, satellite, corporate WAN. Designed specifically for unreliable networks where RTMP would fail.
SRT vs RTMP vs NDI
SRT ✓ For internet
- UDP + retransmission
- Survives packet loss
- AES encryption built-in
- 20ms–8s latency (configurable)
- For internet contribution
- Supported by all pro encoders
RTMP (Legacy)
- TCP — no retransmission
- Packet loss = stream fails
- No native encryption
- Still needed by some platforms
- Use only where SRT unavailable
- Being phased out by broadcasters
NDI (For LAN)
- UDP multicast / unicast
- Local network only
- ~125 Mbps per 1080p stream
- One-frame latency
- Not for internet use
- SRT bridges NDI between sites
💡 The rule: Use NDI inside a building or campus. Use SRT to send video over the internet or cellular networks. Use RTMP only where the destination platform does not yet accept SRT.
Why SRT Replaced RTMP for Broadcast
RTMP (Real-Time Messaging Protocol) was developed by Macromedia in the early 2000s and became the dominant live streaming standard for over a decade. It has significant limitations for professional use:
- No error correction: any packet loss on the network path permanently breaks the stream — a dropped connection cannot recover cleanly
- No encryption: RTMP streams are transmitted in plaintext — content can be intercepted on the network path
- TCP congestion: TCP's congestion control adds latency on poor network paths and causes buffering before failure
- No statistics: RTMP provides no real-time stream health monitoring — you find out there is a problem when viewers report it
SRT resolves all of these issues. By 2024, all major professional encoder manufacturers — Magewell, Kiloview, Haivision, Epiphan, BirdDog, YoloLiv — had adopted SRT as the primary contribution protocol. YouTube, Facebook, Twitch and all major CDNs now accept SRT ingest.
Who Uses SRT
Broadcast News
ENG reporters send live shots over 4G via SRT — replacing satellite and ISDN contribution at a fraction of the cost and weight.
Sports Production
Remote venues use SRT to contribution-encode match feeds to production facilities over internet connections where SDI infrastructure is not installed.
Houses of Worship
SRT's resilience to variable broadband makes it the reliable choice for weekly services where a dropped stream disrupts the congregation.
Corporate Events
External venue internet is unpredictable. SRT from a hardware encoder with 4G backup ensures corporate webcasts reach their audiences.
Medical
SRT's AES encryption makes it suitable for transmitting sensitive clinical video for telemedicine and remote surgical observation.
Defence & Government
SRT AES-256 for secure video contribution over networks where unencrypted transmission is not permitted.
Live Events
SRT contribution from concert and event venues to remote production hubs for multi-camera productions where the production team is offsite.
Education
Campus-to-campus contribution and remote lecture delivery over WAN links with SRT encryption for sensitive academic content.
SRT Hardware at nuuo.co.uk
Hardware encoders with SRT output
Ultra Encode HDMI
H.265 HDMI encoder. SRT, RTMP, HLS and NDI simultaneously from one device. Stream to 4 destinations at once. From £350 ex-VAT.
Pro Convert HDMI Plus
HDMI to NDI and SRT simultaneously. Camera feeds both local NDI network and remote SRT contribution from one encoder. From £383 ex-VAT.
Encoders with 4G / 5G
SRT encoders with built-in SIM slots and bonded cellular. For location streaming where broadband is unavailable or unreliable.
Pearl Encoders
Professional multi-input rack encoders with SRT output. For permanent broadcast facility SRT contribution workflows.
SRT decoders (receive SRT to physical outputs)
Pro Convert NDI to HDMI
Receives SRT alongside NDI and outputs to HDMI. Decode remote SRT contributions to a physical display without a PC. From £370 ex-VAT.
Pro Convert IP to AIO 4K
SRT and NDI to simultaneous 4K HDMI, SDI and analogue. The most capable SRT decoder for broadcast facility integration. From £799 ex-VAT.
Need help with SRT setup or hardware selection?
Our technical team can advise on the right SRT encoder for your network conditions, venue type and production requirements — before your next critical broadcast.
Contact Technical SupportFrequently Asked Questions
What does SRT stand for?
SRT stands for Secure Reliable Transport. It is an open-source protocol developed by Haivision in 2017 and maintained by the SRT Alliance — a 600+ member consortium including Magewell, Kiloview, Epiphan, AWS, Microsoft and all major broadcast technology vendors. SRT is royalty-free.
Why is SRT better than RTMP?
RTMP is TCP-based with no error correction — any packet loss causes the stream to fail. SRT is UDP-based with automatic packet retransmission — streams survive packet loss and network fluctuations without disconnection. SRT includes AES encryption built-in; RTMP is unencrypted. SRT provides live stream statistics; RTMP does not. For professional live contribution over the internet, SRT is significantly more reliable.
Is SRT encrypted?
Yes. SRT includes AES-128 and AES-256 encryption natively. Both encoder and decoder set the same passphrase (10–79 characters) to establish an encrypted connection. Encryption is optional but strongly recommended for sensitive content — medical, legal, corporate or government. Encryption adds negligible processing overhead.
What is SRT latency?
SRT latency is a configurable buffer that gives the protocol time to retransmit lost packets. Set it to 3–4× your measured network RTT (ping time). Local network: 20–40ms. UK broadband: 120–200ms. 4G cellular: 300–500ms. International: 400–1000ms. Both encoder and decoder must be set to the same value. Too low = artefacts. Too high = unnecessary delay.
What is the difference between SRT Caller and Listener?
Listener opens a UDP port and waits. Caller dials out to the Listener's IP and port. One device must be each — two Callers or two Listeners will never connect. Typically: encoder at source = Caller; receiving server or decoder = Listener. Only the Listener needs a firewall port opened inbound. Getting this wrong is the most common SRT connection failure.
Does SRT work over 4G and 5G?
Yes — SRT is specifically designed for unreliable networks including cellular. Set a higher latency buffer for 4G (300–600ms) to account for cellular jitter. For critical location streaming, hardware encoders from Kiloview include SIM card slots and bonded cellular — combining multiple connections for higher bandwidth and resilience.
Which platforms support SRT ingest?
YouTube (verified channels), Facebook Live, Twitch, Wowza Cloud, AWS MediaLive, Akamai, Fastly and Cloudflare Stream all support SRT ingest. RTMP remains more widely supported at the platform level, but SRT adoption is growing rapidly. OBS Studio 28+ supports SRT natively for both streaming and receiving.