Add support for opus in RTP munger (#211)

Author: mickel8

lib/ex_webrtc/rtp/munger.ex

@@ -78,7 +78,11 @@ defmodule ExWebRTC.RTP.Munger do
 
   `clock_rate` is the clock rate of the codec carried in munged RTP packets.
   """
-  @spec new(:h264 | :vp8 | RTPCodecParameters.t(), non_neg_integer()) :: t()
+  @spec new(:opus | :h264 | :vp8 | RTPCodecParameters.t(), non_neg_integer()) :: t()
+  def new(:opus, clock_rate) do
+    %__MODULE__{clock_rate: clock_rate}
+  end
+
   def new(:h264, clock_rate) do
     %__MODULE__{clock_rate: clock_rate}
   end
@@ -89,6 +93,7 @@ defmodule ExWebRTC.RTP.Munger do
 
   def new(%RTPCodecParameters{} = codec_params) do
     case codec_params.mime_type do
+      "audio/opus" -> new(:opus, codec_params.clock_rate)
       "video/H264" -> new(:h264, codec_params.clock_rate)
       "video/VP8" -> new(:vp8, codec_params.clock_rate)
     end