new socket issue

Mark Geib <[email protected]> Thu, 4 Feb 2021 15:04:34 -0700

Newsgroups	gmane.comp.lang.erlang.general
Message-ID	<[email protected]>

In order to join a source-specific multicast group I am trying the new socket module. I am able to join the multicast and start receiving datagrams by spawning the function below. The gen_udp module does not support joining a source-specific multicast currently.

active_socket(Socket, Parent, Timeout) ->
  case socket:recvfrom(Socket, 0, [], Timeout) of
    {ok, {#{port := Port, addr := Addr}, Data}} ->
      Parent ! {udp, Addr, Port, Data},
      active_socket(Socket, Parent, Timeout);

    {error, Reason} ->
      Parent ! {error, socket, Reason},
      active_socket(Socket, Parent, Timeout)

end.

The multicast is a 45Mb RTP MPEG-TS stream. I am able to receive and verify the RTP sequence number successfully. However, about every Timeout period, in the function above, there are a number of datagrams dropped, that is, the RTP sequence number has a gap of about 200. This continues to happen as long as the process runs. Between the drops everything looks fine.

As you can see, my approach is to simply have a recvfrom pending at all times so when a datagram arrives the recvfrom returns, I forward the datagram and call recvfrom again. The Timeout is simply to avoid recvfrom returning with no data.

Thanks,

Mark.

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