SRT, SRTLA and RIST URL builder

SRT, SRTLA and RIST URLs explained

An SRTLA URL looks like srtla://srt.example.com:5000?streamid=abc123. It has three parts: the server address, the port the SRTLA receiver listens on, and the stream ID that tells the server which stream is yours. Moblin, IRL Pro and IRLwhatever take the whole URL in one box. BELABOX asks for each part separately.

An SRT URL for OBS or ffmpeg adds a few options: mode=caller (your computer connects to the server), latency in microseconds (so 2,500 ms is 2500000), and an optional passphrase and pbkeylen for AES encryption.

A RIST URL looks like rist://rist.example.com:5000?buffer=2000. RIST has no stream ID: the server address and port are the stream. The options use the names from librist, the RIST library Moblin, OBS and ffmpeg use: buffer in milliseconds, and username and password for servers that give you a login, or secret with aes-type (128 or 256) for a shared passphrase. Moblin bonds RIST across your connections by itself, so the URL is the same whether you bond or not.

Picking an SRT latency

SRT latency is how long the receiver waits for lost packets to be resent before it gives up on them. Haivision, who created SRT, recommend setting it to a multiple of your round-trip time that grows with packet loss:

From Haivision's SRT deployment guide. The minimum is 20 ms and the maximum 8,000 ms.

Mobile connections are messier than that table assumes: round-trip times jump when you change cell towers and bonded links each have their own. That's why IRL streamers usually set 1,500 to 3,000 ms. For the moments when every link drops, disconnect protection switches to your BRB scene.