Route FFmpeg Tee Outputs to Specific Network Interfaces

When streaming to multiple destinations simultaneously using the FFmpeg tee protocol, you may need to route specific outputs through different network interfaces or physical network adapters. This guide explains how to bind individual target streams within the tee pseudo-muxer to specific local IP addresses, allowing you to control which network interface each stream uses.

The Core Concept: Binding to a Local IP

FFmpeg does not select network interfaces by their system name (like eth0 or wlan0). Instead, it routes traffic through specific network interfaces by binding to the local IP address assigned to that interface.

To route different outputs of a tee stream through different interfaces, you must pass the appropriate local binding options (localaddr or protocol-specific variants) to each target stream inside the tee syntax.

1. Configuring UDP Targets

For UDP streams (often used for MPEG-TS), you can bind to a specific network interface by appending the localaddr parameter directly to the target URL query string.

Syntax:

udp://[destination_ip]:[port]?localaddr=[local_interface_ip]

Example within tee:

ffmpeg -i input.mp4 -map 0 -c copy -f tee \
"[f=mpegts]udp://233.0.0.1:1234?localaddr=192.168.1.50|[f=mpegts]udp://233.0.0.1:1234?localaddr=10.0.0.50"

In this example: * The first stream is routed through the interface with the IP 192.168.1.50. * The second stream is routed through the interface with the IP 10.0.0.50.

2. Configuring RTMP Targets

For RTMP streaming (commonly used for YouTube, Twitch, or Facebook), FFmpeg’s RTMP protocol utilizes the rtmp_localaddr option. Within the tee muxer, you must pass this as a per-output option inside the bracketed prefix.

Syntax:

[f=flv:rtmp_localaddr=[local_interface_ip]]rtmp://[destination_url]

Example within tee:

ffmpeg -i input.mp4 -c:v libx264 -c:a aac -f tee \
"[f=flv:rtmp_localaddr=192.168.1.50]rtmp://a.rtmp.youtube.com/live2/key1|[f=flv:rtmp_localaddr=10.0.0.50]rtmp://live-api-s.facebook.com:80/rtmp/key2"

3. Configuring SRT Targets

For Secure Reliable Transport (SRT) streams, the parameter to bind to a local network adapter is localadapter. This is appended as a query parameter to the SRT URL.

Syntax:

srt://[destination_ip]:[port]?localadapter=[local_interface_ip]

Example within tee:

ffmpeg -i input.mp4 -map 0 -c copy -f tee \
"[f=mpegts]srt://destination1.com:9000?localadapter=192.168.1.50|[f=mpegts]srt://destination2.com:9000?localadapter=10.0.0.50"

Troubleshooting Routing Issues

If your streams are still going through the default gateway instead of the specified interfaces, verify the following:

  1. Active IP Addresses: Ensure the local IP addresses specified in your command are currently assigned to active network adapters on your system.
  2. System Routing Tables: Operating system routing tables can sometimes override FFmpeg’s bind requests. Ensure your OS metric settings do not completely restrict traffic on the secondary interface.
  3. Escaping Characters: In complex terminal environments (like Bash or Zsh), ensure your tee argument is fully enclosed in double quotes to prevent the shell from misinterpreting the ?, &, and | characters.