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SRT Output

Ultra-low latency streaming with the SRT protocol

What is SRT?

SRT (Secure Reliable Transport) is an open-source video transport protocol designed to deliver high-quality, low-latency video across unpredictable networks, including the public internet. Unlike RTMP, SRT was built from the ground up for modern broadcasting workflows and includes built-in error correction, encryption, and congestion control. It is maintained by the SRT Alliance and supported by hundreds of industry vendors.

Ultra-Low Latency

SRT achieves glass-to-glass latency as low as approximately 120 milliseconds under optimal network conditions. This makes it ideal for interactive broadcasts, remote interviews, and real-time production scenarios where delay must be minimized. The protocol's Automatic Repeat reQuest (ARQ) mechanism retransmits lost packets without the overhead of TCP, maintaining both low latency and high reliability.

Listener vs. Caller Mode

SRT connections use a handshake between two roles:

  • Listener mode: StreamDev opens a port and waits for incoming connections. The remote device (caller) initiates the connection. This is best when your server has a public IP and the receiver is behind a firewall or NAT.
  • Caller mode: StreamDev initiates the connection to a remote SRT listener. Use this when the receiving server has a public IP and your StreamDev instance needs to push the stream outward.

Choose the mode based on your network topology. In most contribution-feed setups, the ingest server runs as a listener and the field encoder connects as a caller.

Configurable Latency

StreamDev lets you set the SRT latency buffer anywhere from 20 ms to 8,000 ms. The latency value determines how much buffer the protocol uses for packet retransmission. Lower values reduce delay but leave less room for error recovery; higher values improve reliability on lossy networks at the cost of added delay.

Recommendation: Start with 120–250 ms for local or low-loss networks. For long-distance or unstable connections, increase to 500–2,000 ms for more resilient delivery.

AES Encryption

SRT supports AES encryption to protect your stream in transit. StreamDev offers two encryption levels:

  • AES-128: Fast encryption suitable for most use cases
  • AES-256: Maximum security for sensitive or premium content

Encryption is enabled by setting a passphrase in the stream configuration. Both the sender and receiver must use the same passphrase and encryption key length. Without the correct passphrase, the stream cannot be decoded.

Use Cases

SRT output in StreamDev is designed for professional broadcasting workflows:

  • Contribution feeds: Send high-quality video from the field to a central production facility over the internet, replacing expensive satellite uplinks
  • Remote production: Connect cameras and encoders at a remote venue to your production studio with near-zero delay
  • Inter-server transport: Transfer streams between StreamDev servers or to third-party platforms that accept SRT input