Add Opus payloader (#47)

Author: LVala

examples/send_from_file/example.exs

@@ -18,6 +18,7 @@ defmodule Peer do
     PeerConnection,
     RTPCodecParameters,
     RTP.VP8Payloader,
+    RTP.OpusPayloader,
     RTPTransceiver,
     SessionDescription
   }
@@ -159,7 +160,8 @@ defmodule Peer do
         # that's why you might hear short pauses in audio playback, when using this example
         Process.send_after(self(), :send_audio_packet, duration)
         # values set to 0 are handled by PeerConnection.set_rtp
-        rtp_packet = ExRTP.Packet.new(packet, 0, 0, state.last_audio_timestamp, 0)
+        rtp_packet = OpusPayloader.payload(packet)
+        rtp_packet = %{rtp_packet | timestamp: state.last_audio_timestamp}
         PeerConnection.send_rtp(state.peer_connection, state.audio_track_id, rtp_packet)
 
         # OggReader.next_packet/1 returns duration in ms

lib/ex_webrtc/rtp/opus_payloader.ex

@@ -0,0 +1,15 @@
+defmodule ExWebRTC.RTP.OpusPayloader do
+  @moduledoc """
+  Encapsulates Opus audio packet into an RTP packet.
+  """
+
+  @doc """
+  Packs Opus packet into an RTP packet.
+
+  Fields from RTP header like ssrc, timestamp etc. are set to 0.
+  """
+  @spec payload(binary()) :: ExRTP.Packet.t()
+  def payload(packet) when packet != <<>> do
+    ExRTP.Packet.new(packet, 0, 0, 0, 0)
+  end
+end