WebRTCPublish.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using Unity.WebRTC;
using UnityEngine.Networking;

public class WebRTCPublish : MonoBehaviour{
    RTCPeerConnection peerConnection;
    MediaStreamTrack track;
    Camera cam;

    void Start() {	
      StartCoroutine(WebRTC.Update());
      peerConnection = new RTCPeerConnection();
      peerConnection.OnIceConnectionChange = state => { Debug.Log(state); };
      cam = GetComponent<Camera>();
      track = cam.CaptureStreamTrack(1280, 720);
      peerConnection.AddTrack(track);
      StartCoroutine(DoWHIP());
    }

    IEnumerator DoWHIP() {
      var offer = peerConnection.CreateOffer();
      yield return offer;

      var offerDesc = offer.Desc;
      var opLocal = peerConnection.SetLocalDescription(ref offerDesc);
      yield return opLocal;

      var filteredSdp = "";
      foreach (string sdpLine in offer.Desc.sdp.Split("\r\n")) {
        if (!sdpLine.StartsWith("a=extmap")) {
          filteredSdp += sdpLine + "\r\n";
        }
      }

      Debug.Log(filteredSdp);

      using (UnityWebRequest  www  = new UnityWebRequest("[WHIP URL]")) {
        www.uploadHandler = new UploadHandlerRaw(System.Text.Encoding.ASCII.GetBytes(filteredSdp));
        www.downloadHandler = new DownloadHandlerBuffer();
        www.method = UnityWebRequest.kHttpVerbPOST;
        www.SetRequestHeader("Content-Type", "application/sdp");
        www.SetRequestHeader("Authorization", "Bearer [STAGE PARTICIPANT TOKEN]");
        yield return www.SendWebRequest();
        if (www.result != UnityWebRequest.Result.Success) {
          Debug.Log(www.error);
        } 
        else {
          var answer = new RTCSessionDescription { type = RTCSdpType.Answer, sdp = www.downloadHandler.text };
          var opRemote = peerConnection.SetRemoteDescription(ref answer);
          yield return opRemote;
          if (opRemote.IsError) {
            Debug.Log(opRemote.Error);
          }
        }
      }
    }
    void OnDestroy() {
      peerConnection.Close();
      peerConnection.Dispose();
      track.Dispose();
    }
}