Send TWCC feedbacks when we don't send any packets

Author: LVala

examples/save_to_file/lib/save_to_file/peer_handler.ex

@@ -158,6 +158,12 @@ defmodule SaveToFile.PeerHandler do
     {:ok, state}
   end
 
+  defp handle_webrtc_msg({:rtp, _id, %{payload: <<>>}}, state) do
+    # we're ignoring packets with padding only, as these are most likely used
+    # for network bandwidth probing
+    {:ok, state}
+  end
+
   defp handle_webrtc_msg({:rtp, id, packet}, %{video_track_id: id} = state) do
     state =
       case VP8Depayloader.write(state.video_depayloader, packet) do
@@ -183,8 +189,7 @@ defmodule SaveToFile.PeerHandler do
     opus_packet = OpusDepayloader.depayload(packet)
     {:ok, audio_writer} = Ogg.Writer.write_packet(state.audio_writer, opus_packet)
 
-    state = %{state | audio_writer: audio_writer}
-    {:ok, state}
+    {:ok, %{state | audio_writer: audio_writer}}
   end
 
   defp handle_webrtc_msg(_msg, state), do: {:ok, state}

lib/ex_webrtc/peer_connection.ex

@@ -880,9 +880,8 @@ defmodule ExWebRTC.PeerConnection do
   @impl true
   def handle_info(:send_twcc_feedback, %{twcc_recorder: twcc_recorder} = state) do
     Process.send_after(self(), :send_twcc_feedback, @twcc_interval)
-    %TWCCRecorder{sender_ssrc: sender_ssrc, media_ssrc: media_ssrc} = twcc_recorder
 
-    if sender_ssrc != nil and media_ssrc != nil do
+    if twcc_recorder.media_ssrc != nil do
       {twcc_recorder, feedbacks} = TWCCRecorder.get_feedback(twcc_recorder)
 
       for feedback <- feedbacks do

lib/ex_webrtc/peer_connection/twcc_recorder.ex

@@ -46,9 +46,11 @@ defmodule ExWebRTC.PeerConnection.TWCCRecorder do
   @max_ref_time 0xFFFFFF
   @breakpoint 0x7FFF
 
+  @default_sender_ssrc 1
+
   @type t() :: %__MODULE__{
           media_ssrc: non_neg_integer(),
-          sender_ssrc: non_neg_integer(),
+          sender_ssrc: non_neg_integer() | nil,
           base_seq_no: non_neg_integer() | nil,
           start_seq_no: non_neg_integer() | nil,
           end_seq_no: non_neg_integer() | nil,
@@ -206,7 +208,7 @@ defmodule ExWebRTC.PeerConnection.TWCCRecorder do
     # Pion also caps max number of not_received packets at the beginning
     feedback = %CC{
       media_ssrc: media_ssrc,
-      sender_ssrc: sender_ssrc,
+      sender_ssrc: sender_ssrc || @default_sender_ssrc,
       fb_pkt_count: fb_pkt_count &&& @max_fb_pkt_count,
       base_sequence_number: base_seq_no &&& @max_seq_no,
       packet_status_count: new_base - base_seq_no,