Refactor generate_ssrcs and get_ssrc_attrs

Author: mickel8

lib/ex_webrtc/peer_connection.ex

@@ -1809,7 +1809,7 @@ defmodule ExWebRTC.PeerConnection do
     end
   end
 
-  # See W3C WebRTC 4.4.1.5-4.7.10.1
+  # See W3C WebRTC 4.4.1.4-4.7.10.1
   defp process_mlines_local(_mlines, transceivers, :offer, _owner), do: transceivers
 
   defp process_mlines_local([], transceivers, :answer, _owner), do: transceivers
@@ -1840,7 +1840,7 @@ defmodule ExWebRTC.PeerConnection do
     process_mlines_local(mlines, transceivers, :answer, owner)
   end
 
-  # See W3C WebRTC 4.4.1.5-4.7.10.2
+  # See W3C WebRTC 4.4.1.4-4.7.10.2
   defp process_mlines_remote(mlines, transceivers, sdp_type, demuxer_ssrcs, config, owner) do
     mlines_idx = Enum.with_index(mlines)
     do_process_mlines_remote(mlines_idx, transceivers, sdp_type, demuxer_ssrcs, config, owner)
@@ -1862,12 +1862,7 @@ defmodule ExWebRTC.PeerConnection do
         do: :inactive,
         else: SDPUtils.get_media_direction(mline) |> reverse_direction()
 
-    rtp_sender_ssrcs = Enum.map(transceivers, & &1.sender.ssrc)
-    ssrcs = MapSet.new(demuxer_ssrcs ++ rtp_sender_ssrcs)
-
-    ssrc = do_generate_ssrc(ssrcs)
-    ssrcs = MapSet.put(ssrcs, ssrc)
-    rtx_ssrc = do_generate_ssrc(ssrcs)
+    {ssrc, rtx_ssrc} = generate_ssrcs(transceivers, demuxer_ssrcs)
 
     # Note: in theory we should update transceiver codecs
     # after processing remote track but this shouldn't have any impact
@@ -2198,10 +2193,14 @@ defmodule ExWebRTC.PeerConnection do
   end
 
   defp generate_ssrcs(state) do
-    rtp_sender_ssrcs = Enum.map(state.transceivers, & &1.sender.ssrc)
-    ssrcs = MapSet.new(Map.keys(state.demuxer.ssrc_to_mid) ++ rtp_sender_ssrcs)
-    ssrc = do_generate_ssrc(ssrcs, 200)
-    rtx_ssrc = do_generate_ssrc(MapSet.put(ssrcs, ssrc), 200)
+    generate_ssrcs(state.transceivers, Map.keys(state.demuxer.ssrc_to_mid))
+  end
+
+  defp generate_ssrcs(transceivers, demuxer_ssrcs) do
+    rtp_sender_ssrcs = Enum.map(transceivers, & &1.sender.ssrc)
+    ssrcs = MapSet.new(demuxer_ssrcs ++ rtp_sender_ssrcs)
+    ssrc = do_generate_ssrc(ssrcs)
+    rtx_ssrc = do_generate_ssrc(MapSet.put(ssrcs, ssrc))
     {ssrc, rtx_ssrc}
   end
 

lib/ex_webrtc/rtp_sender.ex

@@ -139,16 +139,13 @@ defmodule ExWebRTC.RTPSender do
     # Don't include track id. See RFC 8829 sec. 5.2.1
     msid_attrs =
       case sender.track do
-        nil ->
+        %MediaStreamTrack{streams: streams} when streams != [] ->
+          Enum.map(streams, &ExSDP.Attribute.MSID.new(&1, nil))
+
+        _other ->
           # In theory, we should do this "for each MediaStream that was associated with the transceiver",
           # but web browsers (chrome, ff) include MSID even when there aren't any MediaStreams
           [ExSDP.Attribute.MSID.new("-", nil)]
-
-        %MediaStreamTrack{streams: streams} ->
-          case Enum.map(streams, &ExSDP.Attribute.MSID.new(&1, nil)) do
-            [] -> [ExSDP.Attribute.MSID.new("-", nil)]
-            other -> other
-          end
       end
 
     ssrc_attrs =
@@ -181,29 +178,37 @@ defmodule ExWebRTC.RTPSender do
   defp get_ssrc_attrs(_pt, _rtx_pt, ssrc, rtx_ssrc, track) do
     streams = (track && track.streams) || []
 
-    case streams do
-      [] ->
-        [
-          %ExSDP.Attribute.SSRCGroup{semantics: "FID", ssrcs: [ssrc, rtx_ssrc]},
-          %ExSDP.Attribute.SSRC{id: ssrc, attribute: "msid", value: "-"},
-          %ExSDP.Attribute.SSRC{id: rtx_ssrc, attribute: "msid", value: "-"}
-        ]
+    fid = %ExSDP.Attribute.SSRCGroup{semantics: "FID", ssrcs: [ssrc, rtx_ssrc]}
 
-      streams ->
-        {ssrc_attrs, rtx_ssrc_attrs} =
-          Enum.reduce(streams, {[], []}, fn stream, {ssrc_attrs, rtx_ssrc_attrs} ->
-            ssrc_attr = %ExSDP.Attribute.SSRC{id: ssrc, attribute: "msid", value: stream}
-            ssrc_attrs = [ssrc_attr | ssrc_attrs]
-
-            rtx_ssrc_attr = %ExSDP.Attribute.SSRC{id: rtx_ssrc, attribute: "msid", value: stream}
-            rtx_ssrc_attrs = [rtx_ssrc_attr | rtx_ssrc_attrs]
-
-            {ssrc_attrs, rtx_ssrc_attrs}
-          end)
+    ssrc_attrs =
+      case streams do
+        [] ->
+          [
+            %ExSDP.Attribute.SSRC{id: ssrc, attribute: "msid", value: "-"},
+            %ExSDP.Attribute.SSRC{id: rtx_ssrc, attribute: "msid", value: "-"}
+          ]
+
+        streams ->
+          {ssrc_attrs, rtx_ssrc_attrs} =
+            Enum.reduce(streams, {[], []}, fn stream, {ssrc_attrs, rtx_ssrc_attrs} ->
+              ssrc_attr = %ExSDP.Attribute.SSRC{id: ssrc, attribute: "msid", value: stream}
+              ssrc_attrs = [ssrc_attr | ssrc_attrs]
+
+              rtx_ssrc_attr = %ExSDP.Attribute.SSRC{
+                id: rtx_ssrc,
+                attribute: "msid",
+                value: stream
+              }
+
+              rtx_ssrc_attrs = [rtx_ssrc_attr | rtx_ssrc_attrs]
+
+              {ssrc_attrs, rtx_ssrc_attrs}
+            end)
+
+          Enum.reverse(ssrc_attrs) ++ Enum.reverse(rtx_ssrc_attrs)
+      end
 
-        fid = %ExSDP.Attribute.SSRCGroup{semantics: "FID", ssrcs: [ssrc, rtx_ssrc]}
-        [fid | Enum.reverse(ssrc_attrs) ++ Enum.reverse(rtx_ssrc_attrs)]
-    end
+    [fid | ssrc_attrs]
   end
 
   @doc false

test/ex_webrtc/rtp_sender_test.exs

@@ -2,7 +2,7 @@ defmodule ExWebRTC.RTPSenderTest do
   use ExUnit.Case, async: true
 
   alias ExRTP.Packet.Extension.SourceDescription
-  alias ExSDP.Attribute.{Extmap, FMTP}
+  alias ExSDP.Attribute.Extmap
 
   alias ExWebRTC.{MediaStreamTrack, RTPCodecParameters, RTPSender}