RTCPeerConnection setting offer sdp does not match the previously generated SDP for this type

[Shushant Arora]

Hi

I have received answer sdp by negotiating offer sdp from peer in different process, Now I Pass answer sdp and offer sdp to separate process and invoke below flow.

var offer_ssdp_string = 'actual offer string'

var answer_sdp_string = 'actual answer string' 

 peerConnection = new RTCPeerConnection(servers);

peerConnection.setLocalDescription(new RTCSessionDescription({ "type": "offer", "sdp": offer_sdp }))

peerConnection.setRemoteDescription(new RTCSessionDescription({ "type": "answer", "sdp": answer_sdp }))

I am getting below errors

 (Uncaught (in promise) DOMException: The SDP does not match the previously generated SDP for this type)

Failed to create session description: InvalidStateError: Failed to execute 'setRemoteDescription' on 'RTCPeerConnection': Failed to set remote answer sdp: Called in wrong state: kStable.

When I recreate offer in another process and then set answer sdp I get error as "Failed to create session description: InvalidAccessError: Failed to execute 'setRemoteDescription' on 'RTCPeerConnection': Failed to set remote answer sdp: The order of m-lines in answer doesn't match order in offer. Rejecting answer.."

peerConnection.createOffer(function(offer) {

     peerConnection.setLocalDescription(offer);

      peerConnection.setRemoteDescription({ "type": "answer", "sdp": answer_sdp })

       

    },

    function(error) {

      trace('setStatus(\'CreateOffer failed!\');')

    });  

Whats the issue in this code flow?

Thanks

[Jehanzaib Younis]

Hi there,

Did you find out the solution for "Failed to execute 'setRemoteDescription' on 'RTCPeerConnection': Failed to set remote answer sdp: The order of m-lines in answer doesn't match order in offer. Rejecting answer" ?

Thank you

[Martynas Padarauskas]

Hey, 

• I believe the first error is because you can't break the flow of a new RTCPeerConnections (create offer -> set local -> set remote -> create answer -> set local -> set remote). If you create offer on one side, answer on the other and only then set the local/remote descriptions it should break by design. 
• Now the second error is a bit more interesting. In my experience this happens if your offer/answer m-lines differ meaning you have more audio/video track devices than you had previously. For further reading try keywords: unified-plan, plan-b. In my case I just stopped using addTracks() and moved to the newer addTransceiver API which fixed the m-lines issue, since know I always have two tracks whether it is chrome, safari, firefox, an old connection, a new connection, doesn't matter.

see if this helps.