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webrtcvideo-streamingstun

webRTC: Video stream plays on local but doesn't play on remote

Architectute

  1. A webPage uses RTCPeerConnection to create a connection. It uses a STUN and a TURN server in its configuration. It creates an offer and sends the Offer to the remote client only after all the candidates have been gathered
if(pc.iceGatheringState === "complete"){
            const resp = await fetch("REMOTE URL", {
                method: "post",
                body: JSON.stringify({
                    offer: btoa(JSON.stringify(pc.localDescription)),
                }),
            });
            const sdp = await resp.text();
            pc.setRemoteDescription(
                new RTCSessionDescription(JSON.parse(atob(sdp)))
            ).catch((e) => console.log(e));
        }

  1. A remote (GO) server uses a REST API to accept the offer and respond with the answer. The answer is sent only after all the candidates have been gathered on the remote peer. I.e. after the "" candidate has been received

  2. The remote server has a local RTP stream which is being sent to the host. The host adds a transceiver before it sends the offer

pc.addTransceiver("video", { direction: "recvonly" });
  1. When an onTrack event is received, the stream is added to a variable and ONLY set as srcObject of the <video> component when the iceConnectionState changes to connected

Issue

The above setup works perfectly in case of a local network. Both, the host and the peer chose a host candidate and the video plays perfectly.

When using a remote connection, both, in case of a STUN (srflx) candidate and a TURN(relay) candidate, the video does not play.

chrome://webrtc-internals clearly shows the the Transport has chosen the right candidates but there is no traffic on the local candidate chosen.

I can see using the UDP dump on the remote peer that the video stream is being sent perfectly.

Debug Info

  1. On remote network, using a srflex candidate, the nack and pli counts are very high compared to a local network
For approx 15 sec of video

pliCount:
 local: 5
 remote: 221

nackCount:
 local: 7
 remote: 2577
Solution

  • That sounds like packet loss to me. There are a few things that could be causing it.

    Can you try lowering the bitrate of what you are sending? See if congestion is causing it.

    Can you trying lowering the MTU? If you are forwarding packets from FFMPEG try appending pkt_size to the URL like this