Multi-Destination Relay#

go-rtmp can forward published streams to one or more external RTMP servers. This enables simulcasting, CDN distribution, and backup recording without any transcoding.

Enabling Relay#

Use the -relay-to flag, which can be specified multiple times:

./rtmp-server -listen :1935 \
  -relay-to rtmp://cdn1.example.com/live/key \
  -relay-to rtmp://cdn2.example.com/live/key

Each destination must use the rtmp:// scheme and include a host. Destinations are validated at startup — invalid URLs cause the server to exit with an error.

Use Cases#

Scenario	Configuration
Simulcast to YouTube + Twitch	`-relay-to rtmp://a.rtmp.youtube.com/live2/yt-key -relay-to rtmp://live.twitch.tv/app/twitch-key`
Forward to CDN origin	`-relay-to rtmp://origin.cdn.example.com/live/ingest`
Backup recording server	`-relay-to rtmp://backup.example.com/live/archive`
Geographic distribution	`-relay-to rtmp://us-east.example.com/live/key -relay-to rtmp://eu-west.example.com/live/key`

How It Works#

When a publisher starts streaming:

The Destination Manager initializes a relay client for each configured destination
Each audio (TypeID 8) and video (TypeID 9) message from the publisher is forwarded
Messages are sent to all destinations in parallel using a WaitGroup
Media is forwarded exactly as received — no transcoding, re-encoding, or modification

Relay runs alongside local subscribers and FLV recording simultaneously. A single published stream can be:

Played by local subscribers
Recorded to FLV
Forwarded to multiple external servers

All at the same time.

Per-Destination Metrics#

Each relay destination tracks its own metrics:

Metric	Type	Description
Status	Enum	`disconnected`, `connecting`, `connected`, or `error`
MessagesSent	Counter	Total messages sent successfully
MessagesDropped	Counter	Messages dropped due to errors
BytesSent	Counter	Total bytes transmitted
LastSentTime	Timestamp	When the last message was sent
ConnectTime	Timestamp	When the connection was established
ReconnectCount	Counter	Number of reconnection attempts

Global relay metrics are also exposed via the metrics endpoint:

rtmp_relay_messages_sent      # Total across all destinations
rtmp_relay_messages_dropped   # Total failures across all destinations
rtmp_relay_bytes_sent         # Total bytes across all destinations

Error Handling#

Relay follows the go-rtmp principle of graceful degradation:

If a destination fails, the error is logged and MessagesDropped is incremented
Other destinations continue receiving media normally
Local subscribers and recording are completely unaffected
Failed sends do not block the publisher

Cleanup#

When the publisher disconnects:

All relay clients are shut down
Destination connections are closed
Metrics reflect the final state

Example: Simulcast Setup#

# Start server with relay to two destinations
./rtmp-server -listen :1935 \
  -relay-to rtmp://a.rtmp.youtube.com/live2/xxxx-xxxx-xxxx-xxxx \
  -relay-to rtmp://live.twitch.tv/app/live_123456789_abcdefg \
  -log-level info

# Publish from OBS or FFmpeg
ffmpeg -re -i test.mp4 -c copy -f flv rtmp://localhost:1935/live/test

# The stream is now live on both YouTube and Twitch simultaneously

You can also combine relay with recording and local subscribers:

./rtmp-server -listen :1935 \
  -record-all true -record-dir ./recordings \
  -relay-to rtmp://cdn.example.com/live/ingest \
  -metrics-addr :8080

# One publisher → local FLV recording + CDN relay + local subscribers + metrics