SRT Protocol

SRT (Secure Reliable Transport) is an open-source low-latency transport protocol developed by Haivision. It provides secure, reliable data transmission over unreliable networks, making it particularly suitable for remote contribution, broadcast-grade ingest, and other scenarios with high network jitter resilience requirements.

Basic Information

Property	Value
Default Port	6000
Transport Layer	UDP (SRT protocol layer)
Publish	✅ Supported
Subscribe	✅ Supported
Latency	120ms+ (configurable)
Feature Flag	`srt`

Configuration

Feature Activation

[features]
srt = ["dep:plugin-srt", "plugin-srt/srt", "srt-tokio"]

The SRT plugin depends on the srt-tokio library, which requires the SRT development library to be installed on the system.

On Ubuntu/Debian:

sudo apt install libsrt-openssl-dev

On macOS:

brew install srt

Configuration File

srt:
  enable: true
  listen_addr: ":6000"
  latency_ms: 120
  max_bandwidth: 0
  passphrase: null

Option	Type	Default	Description
`enable`	bool	`true`	Whether to enable the SRT plugin
`listen_addr`	string	`":6000"`	Listen address
`latency_ms`	u32	`120`	Transport latency (milliseconds)
`max_bandwidth`	u64	`0`	Maximum bandwidth (bytes/sec, 0=unlimited)
`passphrase`	Option	`null`	Encryption passphrase (10-79 characters)

Latency Tuning

latency_ms is the core SRT parameter that controls the buffer latency from sender to receiver:

Low-latency scenarios (LAN): 60-120ms
City-level transport: 120-500ms
Cross-country transport: 500-2000ms

Encrypted Transport

SRT supports AES encryption, configured via passphrase:

srt:
  passphrase: "my-secret-key-12345"

The passphrase must be between 10 and 79 characters. Both the publisher and subscriber must use the same passphrase.

Publishing

Publishing with FFmpeg

# Basic publish
ffmpeg -re -i input.mp4 -c copy -f mpegts "srt://localhost:6000?streamid=publish/live/test"

# Publish with encryption
ffmpeg -re -i input.mp4 -c copy -f mpegts \
  "srt://localhost:6000?streamid=publish/live/test&passphrase=my-secret-key-12345"

# Specify latency parameter
ffmpeg -re -i input.mp4 -c copy -f mpegts \
  "srt://localhost:6000?streamid=publish/live/test&latency=200000"

# Camera capture and publish
ffmpeg -f v4l2 -i /dev/video0 \
  -c:v libx264 -preset ultrafast -tune zerolatency \
  -c:a aac -b:a 128k \
  -f mpegts "srt://localhost:6000?streamid=publish/live/camera"

Publishing with OBS

Go to Settings → Stream
Select Custom for the service
Enter the server URL: srt://your-server:6000?streamid=publish/live/test
Click Start Streaming

StreamID Format

SRT uses the streamid parameter to distinguish between publishing and subscribing:

Publish: streamid=publish/{streamPath}
Subscribe: streamid=subscribe/{streamPath} or streamid=play/{streamPath}

Subscribing

Subscribing with FFplay

ffplay "srt://localhost:6000?streamid=subscribe/live/test"

Recording with FFmpeg

ffmpeg -i "srt://localhost:6000?streamid=subscribe/live/test" -c copy output.mp4

Subscribing with VLC

Open VLC, select Media → Open Network Stream
Enter URL: srt://localhost:6000?streamid=subscribe/live/test
Click Play

Cross-Protocol Forwarding

Streams published via SRT can be played back through other protocols:

# SRT publish
ffmpeg -re -i input.mp4 -c copy -f mpegts \
  "srt://localhost:6000?streamid=publish/live/test"

# Subscribe via RTMP
ffplay rtmp://localhost:1935/live/test

# Subscribe via HTTP-FLV
ffplay http://localhost:8080/flv/live/test.flv

# Subscribe via HLS
ffplay http://localhost:8080/hls/live/test/index.m3u8

SRT vs RTMP

Feature	SRT	RTMP
Transport Layer	UDP	TCP
Latency	Configurable (120ms+)	1-3 seconds
Lossy Network Resilience	Strong (FEC + ARQ)	Weak
Encryption	AES encryption	No built-in encryption
Firewall Friendly	Moderate (UDP)	Good (TCP)
Tool Support	FFmpeg/OBS/vMix	Widespread

SRT significantly outperforms RTMP on lossy networks. It is recommended to use SRT instead of RTMP in the following scenarios:

Remote contribution over the public internet
Mobile network publishing
Environments with unstable network quality