Sending and Receiving custom RTCP packets/events with GStreamer

Question

I am looking to build an MCPTT(Push to talk) kind of application where the Floor Control is handled by sending RTCP packets

RTCP packets in context of MCPTT floor types are as defined at https://www.wireshark.org/docs/dfref/r/rtcp.html (search keyword 'floor')

I am using GStreamer media library for audio video streaming. For example if I have a pipeline as below,

Sender 1:

videotestsrc ! vp8enc ! rtphvp8pay name=pay1 ! udpsink host=X port=5001

Sender 2:

videotestsrc ! vp8enc ! rtphvp8pay name=pay2 ! udpsink host=X port=5002

Receiver:

udpsrc port=5001 ! rtpvp8depay name=depay1 !
                                             input-selector name=select1 ! rtpvp8pay ! udpsink
udpsrc port=5002 ! rtpvp8depay name=depay2 !

I will actually write above in C code, above is only for pipeline representation

Here in above context, based on RTCP floor event sent from pay1/pay2 and received at depay1/depay2 I will control the active sink-pad of input selector

I would like to know how to create a custom RTCP event in GStreamer and send them and receive/parse them at receiver end

Also please suggest if this approach is valid for this kind of use case or any other approach/library suits well here

Answer 1

To handle RTCP you will need to include the rtpbin element in your pipeline. Otherwise you'll only be transferring RTP.

On the receiver side, you need to:

1.Get the RTPSession object from the RtpBin

g_signal_emit_by_name (rtpbin, "get-internal-session", id, &session);

2.Attach to the "on-receiving-rtcp" signal (or to the more specialized ones):

g_signal_connect_after (session, "on-receiving-rtcp",
    G_CALLBACK (on_rtcp_callback), my_callback_data);

3.Look for the RTCP message you want

gst_rtcp_buffer_map (buffer, GST_MAP_READ, &rtcp_buffer));
new_packet = gst_rtcp_buffer_get_first_packet (&rtcp_buffer, &rtcp_packet);

while (gst_rtcp_packet_move_to_next (&rtcp_packet) {
  type = gst_rtcp_packet_get_type (&rtcp_packet);
  switch (type) {
  ...
  }
}

4.And react accordingly, i.e: switch the input selector.

To send, there's an "on-sending-rtcp" on the RTPSession which will allow you to append an RTCP packet of your own. I don't recall if there's a more direct way for this.