[WebRTC] UDP Peer connection issue with non-chromium browsers when client is connect to VPN

Which version are you using?

v1.8.3

Which operating system are you using?

[ ] Linux amd64 standard
[ ] Linux amd64 Docker
[ ] Linux arm64 standard
[x] Linux arm64 Docker
[ ] Linux arm7 standard
[ ] Linux arm7 Docker
[ ] Linux arm6 standard
[ ] Linux arm6 Docker
[ ] Windows amd64 standard
[ ] Windows amd64 Docker (WSL backend)
[ ] macOS amd64 standard
[ ] macOS amd64 Docker
[ ] Other (please describe)

Describe the issue

This issue affects WebRTC clients using Safari (iOS/macOS) and WebKit-based browsers like Chrome on iOS.

WebRTC works as intended in these browsers when NOT connected to a VPN. However, the peer connection fails when the client device is connected to a VPN.

Chromium-based browsers such as Arc, Brave, Chrome, and Opera are not affected by this issue and continue to work with and without the VPN on the same device without any issues.

Firefox is inconsistent when a VPN is enabled. It usually works after reloading the page. Unlike Chromium-based browsers, WebRTC in Firefox only works when using the server's IP address and does not work with loopback addresses like 127.0.0.1 or localhost when connected to a VPN, although these addresses work when not connected to the VPN.

Setting webrtcLocalTCPAddress resolves the issue for WebKit (issues with firefox remain unchanged), which leads me to believe it's some kind of UDP peer issue in WebKit.

Describe how to replicate the issue

Start a path in MediaMTX:

docker run --rm -it \
-e MTX_PATHS_TEST_RUNONINIT="ffmpeg -loglevel error -re -f lavfi -i color=c=blue:s=640x480:r=5 -c:v libx264 -g 1 -f rtsp rtsp://127.0.0.1:8554/test" \
-e MTX_WEBRTCADDITIONALHOSTS=10.0.0.43 \
-p 8189:8189/udp -p 8889:8889 bluenviron/mediamtx:1.8.3-ffmpeg

Confirm WebRTC streams work in a WebKit-based browser and Chromium-based browser
Connect to a VPN like 1.1.1.1 warp or windscribe.
Attempt to open the WebRTC stream in a WebKit-based browser and Chromium-based browser

Did you attach the server logs?

DEB [WebRTC] [session 7d5b5c17] peer connection state: closed
INF [WebRTC] [session 7d5b5c17] closed: deadline exceeded while waiting connection

bluenviron / mediamtx