Group calls

Everything in the quick start is enough for 1:1 calls. To call with more people, also start the SFU server. It handles both signaling and media for group calls, so the Node signaling server isn't used in this mode.

Start the SFU server

You need Go 1.25 or newer. With Go 1.21 to 1.24, go downloads 1.25 by itself the first time.

cd sfu-server
go run .

SFU listening on :4001 (TCP: signaling, UDP: media)
Network access via: ws://192.168.1.10:4001/ws

Clients must reach TCP and UDP port 4001 on that machine: TCP for the WebSocket, UDP for the media of every peer connection. Check it from another device with curl http://192.168.1.10:4001/, which answers {"name":"sfu-server","ok":true}.

Join from the clients

In the lobby of any client, switch to Group call (SFU), set the SFU address once, and join the same room ID from every device.

Client	Default address	What to enter
Web	Port 4001 on the host that serves the page	192.168.1.10:4001 (always include the port on the web)
Android, iOS, Windows	Port 4001 on the signaling server's host	192.168.1.10 (:4001 is added) or a full ws://192.168.1.10:4001/ws
macOS	http://localhost:4001, in Settings (⌘,)	Same as iOS

E2EE works in group calls too. Everyone in the room must use the same setting; the first person to join decides.

Options

Every option is a flag or an environment variable. The flag wins.

Flag	Variable	Default	What it does
-port	PORT	4001	TCP port for HTTP and the WebSocket, and UDP port for media
-public-ip	PUBLIC_IP	none	Address put in the ICE candidates instead of the machine's own. Use it behind a 1:1 NAT, like a cloud VM.
-max-participants	MAX_PARTICIPANTS	8	People per room. The next one gets Room is full.

go run . -max-participants 12
PORT=5000 go run .
go run . -public-ip 203.0.113.7

How many people?

The limit is only a default. There is no simulcast, so every client receives and decodes everyone else's video at full quality: with N people each phone downloads N − 1 videos and the server sends N × (N − 1) streams. Phones usually struggle before the server does, at around 8 to 10 videos. Group calls (SFU) explains why and has a calculator.

Networking

• Firewall. Allow TCP and UDP 4001 (or your -port). macOS asks the first time. On Linux with ufw: sudo ufw allow 4001.
• Cloud VM. Open TCP and UDP 4001 in the security group and start with -public-ip <the VM's public IP>. Without it the WebSocket connects but no video arrives.
• IPv4 and UDP only. There is no TURN server and no TCP fallback for media. Networks that block outgoing UDP can't receive video.
• No TLS. The server speaks ws://. A web client served over HTTPS can't open a ws:// socket, so put a TLS reverse proxy (nginx, Caddy) in front of /ws in that case.
• No authentication. Anyone who can reach the port can join any room. Don't expose it to the internet as is.

More details are in sfu-server/README.md. If something goes wrong, see Troubleshooting.