Reduced-size RTCP (RFC5506) support

[Sebastian Dröge]

On Mon, 2019-02-04 at 06:14 -0600, Ingemar Johansson wrote:
> New to this list and a relative newbie to GStreamer development. I am
> working on an implementation of a SCReAM GStreamer plugin. SCReAM
> (https://tools.ietf.org/html/rfc8298) is a congestion control algorithm for
> realtime low latency media such as video.
> 
> I have reach so far that I am able to insert the SCReAM plugin in both the
> TX and the RX side and I also manage to piggyback RTCP feedback packets
> (https://tools.ietf.org/wg/avtcore/draft-ietf-avtcore-cc-feedback-message/)
> to the normal RTCP RR+SDES packets. 

There is a SCReAM implementation available from here:
  https://github.com/EricssonResearch/openwebrtc-gst-plugins/tree/master/gst/scream
But you're probably aware of that already :)

> I need however to enable reduced-size RTCP (RFC5506) to keep the RTCP
> overhead reasonably small, given that the feedback rate in SCReAM is quite
> high at high bitrates.
> 
> Is there any documentation or examples available that can shed a
> light on this ?

You have to set the RTP profile on the rtpbin (before creating any
sessions) to AVPF or SAVPF. The "rtp-profile" property. That will then
enable the possibility to send reduced size, early RTCP packets for
feedback that is to be sent out before the next regular, big RTCP
packet is to be sent.

There are signals for requesting early RTCP (or generally RTCP) and you
can then attach your additional feedback to those packets.


Note that rtpsession ensures that no more packets than allowed are sent
and also that there's regular RTCP as often as required by the RTP
RFCs.

-- 
Sebastian Dröge, Centricular Ltd · https://www.centricular.com
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