Improve the elixir example

examples/example.exs

@@ -8,7 +8,7 @@ defmodule Peer do
 
   require Logger
 
-  alias ExWebRTC.{IceCandidate, PeerConnection, SessionDescription}
+  alias ExWebRTC.{IceCandidate, PeerConnection, SessionDescription, RTPTransceiver}
 
   @ice_servers [
     # %{urls: "stun:stun.stunprotocol.org:3478"},
@@ -32,7 +32,7 @@ defmodule Peer do
 
         {:ok, pc} = PeerConnection.start_link(ice_servers: @ice_servers)
 
-        {:ok, %{conn: conn, stream: stream, peer_connection: pc}}
+        {:ok, %{conn: conn, stream: stream, peer_connection: pc, other_mid: nil}}
 
       other ->
         Logger.error("Couldn't connect to the signalling server: #{inspect(other)}")
@@ -55,9 +55,10 @@ defmodule Peer do
 
   @impl true
   def handle_info({:gun_ws, _, _, {:text, msg}}, state) do
-    msg
-    |> Jason.decode!()
-    |> handle_ws_message(state)
+    state =
+      msg
+      |> Jason.decode!()
+      |> handle_ws_message(state)
 
     {:noreply, state}
   end
@@ -90,17 +91,22 @@ defmodule Peer do
     :gun.ws_send(state.conn, state.stream, {:text, Jason.encode!(msg)})
 
     track = ExWebRTC.MediaStreamTrack.new(:video)
-    {:ok, transceiver} = PeerConnection.add_transceiver(pc, track)
+    {:ok, _} = PeerConnection.add_transceiver(pc, track)
     {:ok, offer} = PeerConnection.create_offer(pc)
     :ok = PeerConnection.set_local_description(pc, offer)
     msg = %{"type" => "offer", "sdp" => offer.sdp}
     :gun.ws_send(state.conn, state.stream, {:text, Jason.encode!(msg)})
+
+    [_, %RTPTransceiver{mid: mid}] = PeerConnection.get_transceivers(pc)
+
+    %{state | other_mid: mid}
   end
 
   defp handle_ws_message(%{"type" => "answer", "sdp" => sdp}, state) do
     Logger.info("Received SDP answer: #{inspect(sdp)}")
     answer = %SessionDescription{type: :answer, sdp: sdp}
     :ok = PeerConnection.set_remote_description(state.peer_connection, answer)
+    state
   end
 
   defp handle_ws_message(%{"type" => "ice", "data" => data}, state) do
@@ -114,10 +120,13 @@ defmodule Peer do
     }
 
     :ok = PeerConnection.add_ice_candidate(state.peer_connection, candidate)
+
+    state
   end
 
-  defp handle_ws_message(msg, _state) do
+  defp handle_ws_message(msg, state) do
     Logger.info("Received unexpected message: #{inspect(msg)}")
+    state
   end
 
   defp handle_webrtc_message({:ice_candidate, candidate}, state) do
@@ -132,9 +141,13 @@ defmodule Peer do
     :gun.ws_send(state.conn, state.stream, {:text, Jason.encode!(msg)})
   end
 
-  defp handle_webrtc_message({:rtp, mid, packet}, state) do
+  defp handle_webrtc_message({:rtp, _mid, _packet}, %{other_mid: nil}) do
+    Logger.warning("Received RTP, but out transceiver has not beed created")
+  end
+
+  defp handle_webrtc_message({:rtp, _mid, packet}, state) do
     Logger.info("Received RTP: #{inspect(packet)}")
-    PeerConnection.send_rtp(state.peer_connection, "1", packet)
+    PeerConnection.send_rtp(state.peer_connection, state.other_mid, packet)
   end
 
   defp handle_webrtc_message(msg, _state) do