remote SessionDescription semantics does not match configuration: Expected UnifiedPlan, but RemoteDescription is PlanB

[philn]

Your environment.

• Version: 3.3.4 (livekit 1.8.0)
• Browser: experimental webkitgtk build with gstwebrtc enabled
• Other Information - stacktraces, related issues, suggestions how to fix, links for us to have context

What did you do?

Trying to connect to a locally-deployed livekit meet server, this SDP is detected a PlanB:

v=0
o=- 8721044706072616390 0 IN IP4 0.0.0.0
s=-
t=0 0
a=ice-options:trickle
a=group:BUNDLE audio0 video1 application2
m=audio 9 UDP/TLS/RTP/SAVPF 96 9 0 8 110 111 112 113
c=IN IP4 0.0.0.0
a=rtpmap:96 OPUS/48000/2
a=rtpmap:9 G722/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:110 red/48000
a=rtpmap:111 ulpfec/48000
a=rtpmap:112 rtx/48000
a=rtpmap:113 rtx/48000
a=fmtp:96 minptime=10;useinbandfec=1
a=fmtp:112 apt=96
a=fmtp:113 apt=110
a=rtcp-fb:96 nack
a=rtcp-fb:96 transport-cc
a=rtcp-fb:9 nack
a=rtcp-fb:9 transport-cc
a=rtcp-fb:0 nack
a=rtcp-fb:0 transport-cc
a=rtcp-fb:8 nack
a=rtcp-fb:8 transport-cc
a=extmap:1 http://www.ietf.org/id/draft-holmer-rmcat-transport-wide-cc-extensions-01
a=extmap:2 urn:ietf:params:rtp-hdrext:sdes:mid
a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:repaired-rtp-stream-id
a=extmap:4 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=extmap:5 urn:ietf:params:rtp-hdrext:ssrc-audio-level
a=setup:actpass
a=mid:audio0
a=msid:d4dcc506-5542-4f36-afdb-1d9a33c9c6ca 14bac30b-61d9-45eb-9a2c-96d9d80ca56c
a=sendonly
a=ice-ufrag:P2e72cTklZQmw6lW1pTbwDgasAR7jTkS
a=ice-pwd:HODw/p+ARG6dyGB5Iw+nEBOKF+UwSWUr
a=fingerprint:sha-256 85:BD:29:6C:F8:67:8D:A1:9A:FF:28:CB:B5:30:2B:86:CC:D9:29:F1:80:CD:E9:36:6B:54:5A:17:B0:32:45:D6
a=ssrc:2412112442 msid:user2780343522@host-c8ae0a48 webrtctransceiver0
a=ssrc:2412112442 cname:user2780343522@host-c8ae0a48
a=ssrc:2009240965 msid:user2780343522@host-c8ae0a48 webrtctransceiver0
a=ssrc:2009240965 cname:user2780343522@host-c8ae0a48
a=ssrc:4258407968 msid:user2780343522@host-c8ae0a48 webrtctransceiver0
a=ssrc:4258407968 cname:user2780343522@host-c8ae0a48
a=ssrc:1905531733 msid:user2780343522@host-c8ae0a48 webrtctransceiver0
a=ssrc:1905531733 cname:user2780343522@host-c8ae0a48
a=ssrc:2253869690 msid:user2780343522@host-c8ae0a48 webrtctransceiver0
a=ssrc:2253869690 cname:user2780343522@host-c8ae0a48
a=ssrc-group:FID 2412112442 2253869690
a=rtcp-mux
a=rtcp-rsize
m=video 0 UDP/TLS/RTP/SAVPF 108 109 97 98 99 100 101 102 103 104 105 106 107 114
c=IN IP4 0.0.0.0
a=rtpmap:97 H264/90000
a=rtpmap:98 H264/90000
a=rtpmap:99 H264/90000
a=rtpmap:100 H264/90000
a=rtpmap:101 H264/90000
a=rtpmap:102 H264/90000
a=rtpmap:103 H264/90000
a=rtpmap:104 H264/90000
a=rtpmap:105 H265/90000
a=rtpmap:106 AV1/90000
a=rtpmap:107 VP8/90000
a=rtpmap:108 VP9/90000
a=rtpmap:109 VP9/90000
a=rtpmap:114 rtx/90000
a=fmtp:97 level-asymmetry-allowed=1;packetization-mode=1;profile-level-id=42e01f
a=fmtp:98 level-asymmetry-allowed=1;packetization-mode=0;profile-level-id=42e01f
a=fmtp:99 level-asymmetry-allowed=1;packetization-mode=1;profile-level-id=640c1f
a=fmtp:100 level-asymmetry-allowed=1;packetization-mode=0;profile-level-id=640c1f
a=fmtp:101 level-asymmetry-allowed=1;packetization-mode=1;profile-level-id=42001f
a=fmtp:102 level-asymmetry-allowed=1;packetization-mode=0;profile-level-id=42001f
a=fmtp:103 level-asymmetry-allowed=1;packetization-mode=1;profile-level-id=4d001f
a=fmtp:104 level-asymmetry-allowed=1;packetization-mode=0;profile-level-id=4d001f
a=fmtp:108 profile-id=0
a=fmtp:109 profile-id=2
a=fmtp:114 apt=97
a=rtcp-fb:97 nack
a=rtcp-fb:97 nack pli
a=rtcp-fb:97 ccm fir
a=rtcp-fb:97 transport-cc
a=rtcp-fb:98 nack
a=rtcp-fb:98 nack pli
a=rtcp-fb:98 ccm fir
a=rtcp-fb:98 transport-cc
a=rtcp-fb:99 nack
a=rtcp-fb:99 nack pli
a=rtcp-fb:99 ccm fir
a=rtcp-fb:99 transport-cc
a=rtcp-fb:100 nack
a=rtcp-fb:100 nack pli
a=rtcp-fb:100 ccm fir
a=rtcp-fb:100 transport-cc
a=rtcp-fb:101 nack
a=rtcp-fb:101 nack pli
a=rtcp-fb:101 ccm fir
a=rtcp-fb:101 transport-cc
a=rtcp-fb:102 nack
a=rtcp-fb:102 nack pli
a=rtcp-fb:102 ccm fir
a=rtcp-fb:102 transport-cc
a=rtcp-fb:103 nack
a=rtcp-fb:103 nack pli
a=rtcp-fb:103 ccm fir
a=rtcp-fb:103 transport-cc
a=rtcp-fb:104 nack
a=rtcp-fb:104 nack pli
a=rtcp-fb:104 ccm fir
a=rtcp-fb:104 transport-cc
a=rtcp-fb:105 nack
a=rtcp-fb:105 nack pli
a=rtcp-fb:105 ccm fir
a=rtcp-fb:105 transport-cc
a=rtcp-fb:106 nack
a=rtcp-fb:106 nack pli
a=rtcp-fb:106 ccm fir
a=rtcp-fb:106 transport-cc
a=rtcp-fb:107 nack
a=rtcp-fb:107 nack pli
a=rtcp-fb:107 ccm fir
a=rtcp-fb:107 transport-cc
a=rtcp-fb:108 nack
a=rtcp-fb:108 nack pli
a=rtcp-fb:108 ccm fir
a=rtcp-fb:108 transport-cc
a=rtcp-fb:109 nack
a=rtcp-fb:109 nack pli
a=rtcp-fb:109 ccm fir
a=rtcp-fb:109 transport-cc
a=extmap:1 http://www.ietf.org/id/draft-holmer-rmcat-transport-wide-cc-extensions-01
a=extmap:2 urn:ietf:params:rtp-hdrext:sdes:mid
a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:repaired-rtp-stream-id
a=extmap:4 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=extmap:5 http://www.webrtc.org/experiments/rtp-hdrext/color-space
a=extmap:6 https://aomediacodec.github.io/av1-rtp-spec/#dependency-descriptor-rtp-header-extension
a=setup:actpass
a=mid:video1
a=msid:fecc8f07-1e45-4491-9078-fecbf715dadb 621a2696-6db5-430f-b885-a2fd98a208f2
a=sendonly
a=ice-ufrag:P2e72cTklZQmw6lW1pTbwDgasAR7jTkS
a=ice-pwd:HODw/p+ARG6dyGB5Iw+nEBOKF+UwSWUr
a=fingerprint:sha-256 85:BD:29:6C:F8:67:8D:A1:9A:FF:28:CB:B5:30:2B:86:CC:D9:29:F1:80:CD:E9:36:6B:54:5A:17:B0:32:45:D6
a=ssrc:578602538 msid:user2780343522@host-c8ae0a48 webrtctransceiver1
a=ssrc:578602538 cname:user2780343522@host-c8ae0a48
a=ssrc:1960793915 msid:user2780343522@host-c8ae0a48 webrtctransceiver1
a=ssrc:1960793915 cname:user2780343522@host-c8ae0a48
a=ssrc:890918086 msid:user2780343522@host-c8ae0a48 webrtctransceiver1
a=ssrc:890918086 cname:user2780343522@host-c8ae0a48
a=ssrc:1454815906 msid:user2780343522@host-c8ae0a48 webrtctransceiver1
a=ssrc:1454815906 cname:user2780343522@host-c8ae0a48
a=ssrc:3834637145 msid:user2780343522@host-c8ae0a48 webrtctransceiver1
a=ssrc:3834637145 cname:user2780343522@host-c8ae0a48
a=ssrc:2256176958 msid:user2780343522@host-c8ae0a48 webrtctransceiver1
a=ssrc:2256176958 cname:user2780343522@host-c8ae0a48
a=ssrc:1364677151 msid:user2780343522@host-c8ae0a48 webrtctransceiver1
a=ssrc:1364677151 cname:user2780343522@host-c8ae0a48
a=ssrc:3843409207 msid:user2780343522@host-c8ae0a48 webrtctransceiver1
a=ssrc:3843409207 cname:user2780343522@host-c8ae0a48
a=ssrc:288295172 msid:user2780343522@host-c8ae0a48 webrtctransceiver1
a=ssrc:288295172 cname:user2780343522@host-c8ae0a48
a=ssrc:123532235 msid:user2780343522@host-c8ae0a48 webrtctransceiver1
a=ssrc:123532235 cname:user2780343522@host-c8ae0a48
a=ssrc:1783185158 msid:user2780343522@host-c8ae0a48 webrtctransceiver1
a=ssrc:1783185158 cname:user2780343522@host-c8ae0a48
a=ssrc:1550974677 msid:user2780343522@host-c8ae0a48 webrtctransceiver1
a=ssrc:1550974677 cname:user2780343522@host-c8ae0a48
a=ssrc:2936330432 msid:user2780343522@host-c8ae0a48 webrtctransceiver1
a=ssrc:2936330432 cname:user2780343522@host-c8ae0a48
a=ssrc:2217239020 msid:user2780343522@host-c8ae0a48 webrtctransceiver1
a=ssrc:2217239020 cname:user2780343522@host-c8ae0a48
a=ssrc-group:FID 578602538 2217239020
a=rtcp-mux
a=rtcp-rsize
a=bundle-only
m=application 0 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 0.0.0.0
a=setup:actpass
a=mid:application2
a=ice-ufrag:P2e72cTklZQmw6lW1pTbwDgasAR7jTkS
a=ice-pwd:HODw/p+ARG6dyGB5Iw+nEBOKF+UwSWUr
a=fingerprint:sha-256 85:BD:29:6C:F8:67:8D:A1:9A:FF:28:CB:B5:30:2B:86:CC:D9:29:F1:80:CD:E9:36:6B:54:5A:17:B0:32:45:D6
a=bundle-only
a=sctp-port:5000

What did you expect?

Unified plan ;)

What happened?

[Sean-Der]

Instead of a regex this should just explicitly check for audio, video or data.

I will open a PR for that @philn !

[Sean-Der]

Hey @philn

Sorry I was wrong. This SDP is Plan-B (I believe?)

The multiple a=ssrc lines in the video media section would cause it be parsed as Plan-B. The all have the same cname/msid though.

This is a strange bug. Is it easy to get LiveKit to produce an SDP like this?

[philn]

In the unified plan proposal, section 3.3 there's this:

In cases where a media source needs to correspond to more than one
RTP flow, e.g. RTX, FEC, or simulcast, the a=ssrc-group [RFC5576]
concept is used to create a grouping of SSRCs for a single media
stream track. Each SSRC is declared using a=ssrc attributes, the
same MSID is shared between the SSRCs, and the a=ssrc-group attribute
defines the behavior of the grouped SSRCs.

So iiuc, having the same MSID should be OK in unified plan?

This is not trivial to reproduce, you'd need a development build of webkitgtk with a specific branch (that i can share) and a locally deployed livekit instance (so that the livekit/pion logs are visible).