TWCC stats are null with send-only connection to chrome in master

Faraz Khan farazrkhan at gmail.com
Sat Oct 10 04:23:50 UTC 2020


Got it working. Had to add RTP caps 'extmap-3=
http://www.ietf.org/id/draft-holmer-rmcat-transport-wide-cc-extensions-01'
to application/x-rtp. Works like a charm.

Are negative delta of delta averages expected? What does that mean?


On Thu, Oct 8, 2020 at 8:15 PM Faraz Khan <farazrkhan at gmail.com> wrote:

> Trying to get TWCC stats working in my gstreamer build (master from two
> days ago). My pipeline is a h264 video + audio webrtc stream with the
> following changes made to the offer SDP manually (to add goog-remb and
> transport-cc):
>
> v=0
> o=- 3207024576269204753 0 IN IP4 0.0.0.0
> s=-
> t=0 0
> a=ice-options:trickle
> a=group:BUNDLE video0 audio1 application2
> m=video 9 UDP/TLS/RTP/SAVPF 96
> c=IN IP4 0.0.0.0
> a=setup:actpass
> a=ice-ufrag:4QpOTwCuN51rZuwazlwaPpgec+tL7R/b
> a=ice-pwd:T5les5UrI/8Bk6bpUSK1X4JF2phqaGdq
> a=rtcp-mux
> a=rtcp-rsize
> a=sendrecv
> a=rtpmap:96 H264/90000
> a=rtcp-fb:96 nack pli
> a=rtcp-fb:96 goog-remb
> a=rtcp-fb:96 transport-cc
> a=framerate:30
> a=fmtp:96
> packetization-mode=1;profile-level-id=42c028;sprop-parameter-sets=Z0LAKNoB4AiflwFqAgICgAAAAwCAAAAeR4wZUA==,aM48gA==
> a=ssrc:4020551879 msid:user2637538205 at host-f7c25563 webrtctransceiver0
> a=ssrc:4020551879 cname:user2637538205 at host-f7c25563
> a=mid:video0
>
> When I try to do twcc-stats on my rtpsession it doesn't seem to work:
>
> GstElement* rtpbin = gst_bin_get_by_name(GST_BIN(webrtcbin), "rtpbin");
> g_signal_emit_by_name(rtpbin, "get-session", 0, &session);
> if (session != NULL) {
>        g_object_get(G_OBJECT(session), "stats", &stats, NULL);
>        gst_structure_foreach(stats, on_stats_iter, (gpointer)stats);
>         std::cout << std::endl;
>         g_object_get(G_OBJECT(session), "twcc-stats", &twcstats, NULL);
>         gst_structure_foreach(twcstats, on_stats_iter, (gpointer)twcstats);
> }
>
>
> I can get "stats" no problem but twcc-stats is null.
>
> I'm running with GST_RTP_ENABLE_EXPERIMENTAL_TWCC_PROPERTY=1 as well.
>
> Any ideas? I don't get REMB packets from chrome either - I wonder if
> chrome needs to transmit a stream for all this to work for some reason?
>
> Thanks!
>
>
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