Wrong "a=mid:" identification-tag in SDP for video

[BRFCommend]

Hello dear SIP.js Team,

I have followiing behavior.

1. I send an invite, which contain only audio:

v=0
o=- 6487371386765808549 2 IN IP4 127.0.0.1
s=-
t=0 0
a=group:BUNDLE 0
a=extmap-allow-mixed
a=msid-semantic: WMS b5fa3720-4d43-4908-83bf-922e3e85d189
m=audio 21218 UDP/TLS/RTP/SAVPF 111 63 103 104 9 0 8 106 105 13 110 112 113 126
c=IN IP4 195.70.114.111
a=rtcp:9 IN IP4 0.0.0.0
a=candidate:36711831 1 tcp 1518283007 2a02:16a8:dc:aff:41ff:7a05:aabe:ea75 9 typ host tcptype active generation 0 network-id 4
a=candidate:1459951043 1 tcp 1518217471 2a02:16a8:dc:aff:bc63:1125:3d23:ccb7 9 typ host tcptype active generation 0 network-id 5
a=candidate:1127467076 1 tcp 1518149375 172.19.128.1 9 typ host tcptype active generation 0 network-id 1
a=candidate:940248979 1 tcp 1518083839 192.168.249.22 9 typ host tcptype active generation 0 network-id 2
a=candidate:696139521 1 tcp 1518018303 192.168.178.22 9 typ host tcptype active generation 0 network-id 3
a=candidate:1286852967 1 udp 2122262783 2a02:16a8:dc:aff:41ff:7a05:aabe:ea75 61929 typ host generation 0 network-id 4
a=candidate:428271923 1 udp 2122197247 2a02:16a8:dc:aff:bc63:1125:3d23:ccb7 61930 typ host generation 0 network-id 5
a=candidate:229651636 1 udp 2122129151 172.19.128.1 61931 typ host generation 0 network-id 1
a=candidate:1988686691 1 udp 2122063615 192.168.249.22 61932 typ host generation 0 network-id 2
a=candidate:1744684017 1 udp 2121998079 192.168.178.22 61933 typ host generation 0 network-id 3
a=candidate:2876308578 1 udp 1685790463 195.70.114.111 21218 typ srflx raddr 192.168.178.22 rport 61933 generation 0 network-id 3
a=candidate:3120942320 1 udp 1685855999 80.120.59.162 46995 typ srflx raddr 192.168.249.22 rport 61932 generation 0 network-id 2
a=ice-ufrag:XS3k
a=ice-pwd:j8j0QnwWORfxTD2uwXe2h4/L
a=ice-options:trickle
a=fingerprint:sha-256 BB:D7:1C:65:9F:65:4F:F1:BB:26:67:0F:B6:FD:51:D1:1F:42:54:65:3A:49:52:28:DD:38:4C:BF:A2:FD:CF:B4
a=setup:actpass
a=mid:0
a=extmap:1 urn:ietf:params:rtp-hdrext:ssrc-audio-level
a=extmap:2 http://www.webrtc.org/experiments/rtp-hdrext/abs-send-time
a=extmap:3 http://www.ietf.org/id/draft-holmer-rmcat-transport-wide-cc-extensions-01
a=extmap:4 urn:ietf:params:rtp-hdrext:sdes:mid
a=sendrecv
a=msid:b5fa3720-4d43-4908-83bf-922e3e85d189 6df34184-2a9d-47fe-85f0-96c2e4459064
a=rtcp-mux
a=rtpmap:111 opus/48000/2
a=rtcp-fb:111 transport-cc
a=fmtp:111 minptime=10;useinbandfec=1
a=rtpmap:63 red/48000/2
a=fmtp:63 111/111
a=rtpmap:103 ISAC/16000
a=rtpmap:104 ISAC/32000
a=rtpmap:9 G722/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:106 CN/32000
a=rtpmap:105 CN/16000
a=rtpmap:13 CN/8000
a=rtpmap:110 telephone-event/48000
a=rtpmap:112 telephone-event/32000
a=rtpmap:113 telephone-event/16000
a=rtpmap:126 telephone-event/8000
a=ssrc:173696517 cname:oOk4E6XnJI5qXBO4
a=ssrc:173696517 msid:b5fa3720-4d43-4908-83bf-922e3e85d189 6df34184-2a9d-47fe-85f0-96c2e4459064
a=ssrc:173696517 mslabel:b5fa3720-4d43-4908-83bf-922e3e85d189
a=ssrc:173696517 label:6df34184-2a9d-47fe-85f0-96c2e4459064

2. I get a Re-Invite back from other Peer, which contains audio and video:

v=0
o=- 2587202469 5 IN IP4 168.63.9.134
s=Commend
c=IN IP4 168.63.9.134
t=0 0
m=audio 27736 RTP/SAVP 111 9 8 0
a=maxptime:20
a=mid:0
a=rtpmap:111 opus/48000/2
a=rtpmap:9 G722/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:0 PCMU/8000
a=fmtp:111 useinbandfec=1
a=sendrecv
a=rtcp:27737
a=rtcp-mux
a=setup:actpass
a=fingerprint:sha-1 72:AD:6C:9B:65:58:60:32:28:6C:69:9F:0C:A7:B1:36:E7:67:1F:8E
a=ptime:20
a=ice-ufrag:KgNA0ytg
a=ice-pwd:9auF5FrqwACfGoX3zIQeXX3LtZ
a=ice-options:trickle
a=candidate:sItLLPWORbggr2b1 1 UDP 2130706431 168.63.9.134 27736 typ host
a=candidate:sItLLPWORbggr2b1 2 UDP 2130706430 168.63.9.134 27737 typ host
a=end-of-candidates
m=video 27804 RTP/SAVP 99
a=rtpmap:99 H264/90000
a=sendrecv
a=rtcp:27805
a=rtcp-mux
a=setup:actpass
a=fingerprint:sha-1 72:AD:6C:9B:65:58:60:32:28:6C:69:9F:0C:A7:B1:36:E7:67:1F:8E
a=ice-ufrag:NxZM89gT
a=ice-pwd:0hBE3a6zujN7gJBonZhxrHwVVK
a=candidate:sItLLPWORbggr2b1 1 UDP 2130706431 168.63.9.134 27804 typ host
a=candidate:sItLLPWORbggr2b1 2 UDP 2130706430 168.63.9.134 27805 typ host

As you can see there is no a=mid attribute for video.

Question: Can the missing mid attribute (in the Re-Invite) lead to a=mid:2 attribute for video in a 200 Ok Response?

Because this is the outcome in this SDP:

v=0
o=- 6487371386765808549 3 IN IP4 127.0.0.1
s=-
t=0 0
a=msid-semantic: WMS b5fa3720-4d43-4908-83bf-922e3e85d189
m=audio 21218 RTP/SAVP 111 9 8 0
c=IN IP4 195.70.114.111
a=rtcp:9 IN IP4 0.0.0.0
a=candidate:36711831 1 tcp 1518283007 2a02:16a8:dc:aff:41ff:7a05:aabe:ea75 9 typ host tcptype active generation 0 network-id 4
a=candidate:1459951043 1 tcp 1518217471 2a02:16a8:dc:aff:bc63:1125:3d23:ccb7 9 typ host tcptype active generation 0 network-id 5
a=candidate:1127467076 1 tcp 1518149375 172.19.128.1 9 typ host tcptype active generation 0 network-id 1
a=candidate:940248979 1 tcp 1518083839 192.168.249.22 9 typ host tcptype active generation 0 network-id 2
a=candidate:696139521 1 tcp 1518018303 192.168.178.22 9 typ host tcptype active generation 0 network-id 3
a=candidate:1286852967 1 udp 2122262783 2a02:16a8:dc:aff:41ff:7a05:aabe:ea75 61929 typ host generation 0 network-id 4
a=candidate:428271923 1 udp 2122197247 2a02:16a8:dc:aff:bc63:1125:3d23:ccb7 61930 typ host generation 0 network-id 5
a=candidate:229651636 1 udp 2122129151 172.19.128.1 61931 typ host generation 0 network-id 1
a=candidate:1988686691 1 udp 2122063615 192.168.249.22 61932 typ host generation 0 network-id 2
a=candidate:1744684017 1 udp 2121998079 192.168.178.22 61933 typ host generation 0 network-id 3
a=candidate:2876308578 1 udp 1685790463 195.70.114.111 21218 typ srflx raddr 192.168.178.22 rport 61933 generation 0 network-id 3
a=candidate:3120942320 1 udp 1685855999 80.120.59.162 46995 typ srflx raddr 192.168.249.22 rport 61932 generation 0 network-id 2
a=ice-ufrag:XS3k
a=ice-pwd:j8j0QnwWORfxTD2uwXe2h4/L
a=ice-options:trickle
a=fingerprint:sha-256 BB:D7:1C:65:9F:65:4F:F1:BB:26:67:0F:B6:FD:51:D1:1F:42:54:65:3A:49:52:28:DD:38:4C:BF:A2:FD:CF:B4
a=setup:passive
a=mid:0
a=sendrecv
a=msid:b5fa3720-4d43-4908-83bf-922e3e85d189 6df34184-2a9d-47fe-85f0-96c2e4459064
a=rtcp-mux
a=rtpmap:111 opus/48000/2
a=fmtp:111 minptime=10;useinbandfec=1
a=rtpmap:9 G722/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:0 PCMU/8000
a=ssrc:173696517 cname:oOk4E6XnJI5qXBO4
a=ssrc:173696517 msid:b5fa3720-4d43-4908-83bf-922e3e85d189 6df34184-2a9d-47fe-85f0-96c2e4459064
a=ssrc:173696517 mslabel:b5fa3720-4d43-4908-83bf-922e3e85d189
a=ssrc:173696517 label:6df34184-2a9d-47fe-85f0-96c2e4459064
m=video 64355 RTP/SAVP 99
c=IN IP4 172.19.128.1
a=rtcp:9 IN IP4 0.0.0.0
a=candidate:36711831 1 tcp 1518283007 2a02:16a8:dc:aff:41ff:7a05:aabe:ea75 9 typ host tcptype active generation 0 network-id 4
a=candidate:1459951043 1 tcp 1518217471 2a02:16a8:dc:aff:bc63:1125:3d23:ccb7 9 typ host tcptype active generation 0 network-id 5
a=candidate:1127467076 1 tcp 1518149375 172.19.128.1 9 typ host tcptype active generation 0 network-id 1
a=candidate:940248979 1 tcp 1518083839 192.168.249.22 9 typ host tcptype active generation 0 network-id 2
a=candidate:696139521 1 tcp 1518018303 192.168.178.22 9 typ host tcptype active generation 0 network-id 3
a=candidate:1286852967 1 udp 2122262783 2a02:16a8:dc:aff:41ff:7a05:aabe:ea75 64353 typ host generation 0 network-id 4
a=candidate:428271923 1 udp 2122197247 2a02:16a8:dc:aff:bc63:1125:3d23:ccb7 64354 typ host generation 0 network-id 5
a=candidate:229651636 1 udp 2122129151 172.19.128.1 64355 typ host generation 0 network-id 1
a=candidate:1988686691 1 udp 2122063615 192.168.249.22 64356 typ host generation 0 network-id 2
a=candidate:1744684017 1 udp 2121998079 192.168.178.22 64357 typ host generation 0 network-id 3
a=ice-ufrag:c25J
a=ice-pwd:xXnYN0tY48GjKzldtGnXM5Y2
a=ice-options:trickle
a=fingerprint:sha-256 BB:D7:1C:65:9F:65:4F:F1:BB:26:67:0F:B6:FD:51:D1:1F:42:54:65:3A:49:52:28:DD:38:4C:BF:A2:FD:CF:B4
a=setup:active
a=mid:2
a=sendrecv
a=msid:- 53e27296-b5bd-4d5a-b0e0-8707094a7086
a=rtcp-mux
a=rtpmap:99 H264/90000
a=fmtp:99 level-asymmetry-allowed=1;packetization-mode=0;profile-level-id=42e01f
a=ssrc:1216605974 cname:oOk4E6XnJI5qXBO4
a=ssrc:1216605974 msid:- 53e27296-b5bd-4d5a-b0e0-8707094a7086
a=ssrc:1216605974 mslabel:-
a=ssrc:1216605974 label:53e27296-b5bd-4d5a-b0e0-8707094a7086

Video contains a=mid:2, although it should be a=mid:1
How can this be?

Version: 0.20.0

Thank you very much!