How can I use webrtc offline

I'm developing a Vuejs app that among other things displays several RTSP streams in the browser. For converting the streams and displaying them I'm using RTSPtoWebRTC with WebRtcPlayer. I decided to use WebRTC because of the low latency (this is a robotics project). This method is working fine and I can view all the streams with a max latency of 50ms. But as soon as I disconnect from the internet I get an error:

Uncaught DOMException: Can't create RTCPeerConnections when the network is down

I cant count that this robot will have an internet connection at all time, this isnt the intent.

I tried several solutions like removing any mention of external iceServers from the player and the server.

      iceServers: [{
        urls: ["stun:stun.l.google.com:19302"]
      }]

Tried running my own STUN/TURN server with coturn and supplying the ip address as an ICE server but to no success - still same no internet error.

I'm running the app on Firefox if this matters and I found this post from a while back: firefox bug report about this issue

I tried the suggestion there of trying to set media.peerconnection.ice.loopback in about:config to true but still doesn't work.

Help is much appreciated!

Edit:

So, after spending too many hours trying to solve this I found that in Chrome this works offline just fine. So I’ll just stick to that

Solution

The error gets thrown here in Firefox code: https://searchfox.org/mozilla-central/source/dom/media/PeerConnection.jsm#473

The workaround with the loopback interface no longer works if I read that code correct. The if condition in the code just asks the networking code if there is any network connectivity.

So you either

try Phillips suggestion of making one network interface believe it still has connectivity. Maybe a fake interface with a hard coded IP address, but no default route would be enough.
Or you convince the Mozilla developers that there are reasonable use cases for using PeerConnections in offline scenarios to drop that check in Firefox - although I would be concerned that it might run into another error further down in the code. Or you could try to submit a patch yourself.