A demo of broadcasting directly to Twitch from a game built in Unity.

TwitchPublish.cs

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

[RequireComponent(typeof(AudioListener))]
public class TwitchPublish : MonoBehaviour
{
  RTCPeerConnection peerConnection;
  MediaStreamTrack videoTrack;
  MediaStreamTrack audioTrack;
  RenderTexture renderTexture;
  Texture2D screenshotTexture;
  string twitchStreamKey = "";
  public Button broadcastButton;

  void Start()
  {
    StartCoroutine(WebRTC.Update());
    peerConnection = new RTCPeerConnection();
    peerConnection.OnIceConnectionChange = state => { Debug.Log(state); };
    screenshotTexture = new Texture2D(1280, 720, TextureFormat.RGB24, false);
    renderTexture = new RenderTexture(1280, 720, 24);
    videoTrack = new VideoStreamTrack(renderTexture);
    peerConnection.AddTrack(videoTrack);
    AudioListener audioListener = GetComponent<AudioListener>();
    audioTrack = new AudioStreamTrack(audioListener)
    {
      Loopback = true
    };
    peerConnection.AddTrack(audioTrack);
    broadcastButton.interactable = false;
  }

  public void SetStreamKey(string s)
  {
    twitchStreamKey = s;
    broadcastButton.interactable = s.Length > 0;
  }

  public void Broadcast()
  {
    StartCoroutine(DoWHIP());
  }

  IEnumerator RecordFrame()
  {
    yield return new WaitForEndOfFrame();
    RenderTexture tempTexture = RenderTexture.GetTemporary(Screen.width, Screen.height, 24, RenderTextureFormat.ARGB32, RenderTextureReadWrite.Default, 1);
    ScreenCapture.CaptureScreenshotIntoRenderTexture(tempTexture);
    RenderTexture transformedTexture = RenderTexture.GetTemporary(1280, 720, 24, RenderTextureFormat.ARGB32, RenderTextureReadWrite.Default, 1);
    Graphics.Blit(tempTexture, transformedTexture, new Vector2(1, -1), new Vector2(0, 1));
    Graphics.Blit(transformedTexture, renderTexture);
    RenderTexture.ReleaseTemporary(tempTexture);
    screenshotTexture.ReadPixels(new Rect(0, 0, 1280, 720), 0, 0);
    RenderTexture.ReleaseTemporary(transformedTexture);
    screenshotTexture.Apply();
  }

  void LateUpdate()
  {
    StartCoroutine(RecordFrame());
  }

  IEnumerator DoWHIP()
  {
    peerConnection.AddTransceiver(TrackKind.Audio);
    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";
      }
    }

    using (UnityWebRequest www = new UnityWebRequest("https://g.webrtc.live-video.net:4443/v2/offer"))
    {
      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 " + twitchStreamKey);
      yield return www.SendWebRequest();
      if (www.result != UnityWebRequest.Result.Success)
      {
        Debug.Log(JsonUtility.ToJson(www.result, true));
        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()
  {
    if (peerConnection != null)
    {
      peerConnection.Close();
      peerConnection.Dispose();

    }
    if (videoTrack != null) videoTrack.Dispose();
    if (audioTrack != null) audioTrack.Dispose();
  }
}