Sdp Plan-b UnifiedPlan

Unified Plan and Plan B were two competing IETF drafts for the negotiation and exchange of multiple media sources (AKA MediaStreamTracks, or MSTs) between two WebRTC endpoints. 
Unified Plan 和 Plan B 和 Plan A是SDP協商中，多路媒體流的協商方式。

unified-plan文檔

unified-plan

Plan-b 和 Unified-plan 區別

In Plan B, one m= section is used for audio and one m= section is used for video, with the media stream identification attribute, or mid, set to “audio” or “video” respectively. If multiple tracks of the same kind are in an offer, multiple a=ssrc lines are listed under the same m= section.

In Unified Plan, one m= section means one sending and/or one receiving track. The mid is its identifier. If multiple tracks are used, multiple m= sections are created。

• 在Plan-b中， 音頻只有一個m=, 視頻只有一個m＝ 。 當有多路媒體流時， 根據ssrc 區分。
• 在Unified-plan 中， 每路流都有一個m=。
• 當只有一個路視頻流，一路音頻流時，兩者格式兼容。
• 對比下圖中，發送兩路音頻流時的區別。

plan-b	unified-plan

其它

1. https://tools.ietf.org/html/draft-roach-mmusic-unified-plan-00
2. chrome 支持計劃：https://webrtc.org/web-apis/chrome/unified-plan/
3. firefox 支持unified-plan， mid 長度不能超過16位
4. chrome unified-plan 需要確保協商結束後發送視頻流，否則會 Failed to set local answer sdp: Failed to process the bundled m= section.
5. 修改chrome://flags 設置sdp 格式
6. chrome 下72 默認格式unified-plan ， 通過getConfiguration 查看當前peer 格式， 在低版本的chrome裏，就算強制聲明參數unified-plan ，還是會使用plan-b。格式以getConfiguration 返回的爲準。

type: offer, sdp: v=0
o=mediasoup 76760093 1 IN IP4 0.0.0.0
s=-
t=0 0
a=ice-lite
a=fingerprint:sha-256 75:E9:8A:3C:96:49:89:97:18:A3:0D:73:E9:9A:59:D1:8A:B4:15:A9:8F:C4:DE:91:8F:5D:E3:73:0D:E2:00:4E
a=msid-semantic: WMS *
a=group:BUNDLE audio-1 video-1 j6gtnlva p0o0fho7 i860vo1m xwa9siz1
m=audio 7 RTP/SAVPF 100
c=IN IP4 127.0.0.1
a=rtpmap:100 opus/48000/2
a=fmtp:100 minptime=10;useinbandfec=1
a=extmap:1 urn:ietf:params:rtp-hdrext:ssrc-audio-level
a=extmap:5 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=setup:actpass
a=mid:audio-1
a=recvonly
a=ice-ufrag:3lw1e76eix7edjcm
a=ice-pwd:cidqjcjfv28re4t7djaf410gkzpoblq4
a=candidate:udpcandidate 1 udp 1078862079 10.1.133.155 19211 typ host
a=end-of-candidates
a=ice-options:renomination
a=rtcp-mux
a=rtcp-rsize
m=video 7 RTP/SAVPF 123 101
c=IN IP4 127.0.0.1
a=rtpmap:123 VP8/90000
a=rtpmap:101 rtx/90000
a=fmtp:101 apt=123
a=rtcp-fb:123 goog-remb
a=rtcp-fb:123 ccm fir
a=rtcp-fb:123 nack
a=rtcp-fb:123 nack pli
a=extmap:2 urn:ietf:params:rtp-hdrext:toffset
a=extmap:3 http://www.webrtc.org/experiments/rtp-hdrext/abs-send-time
a=extmap:4 urn:3gpp:video-orientation
a=extmap:5 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=setup:actpass
a=mid:video-1
a=recvonly
a=ice-ufrag:3lw1e76eix7edjcm
a=ice-pwd:cidqjcjfv28re4t7djaf410gkzpoblq4
a=candidate:udpcandidate 1 udp 1078862079 10.1.133.155 19211 typ host
a=end-of-candidates
a=ice-options:renomination
a=rtcp-mux
a=rtcp-rsize
m=video 7 RTP/SAVPF 123 101
c=IN IP4 127.0.0.1
a=rtpmap:123 VP8/90000
a=rtpmap:101 rtx/90000
a=fmtp:101 apt=123
a=rtcp-fb:123 goog-remb
a=rtcp-fb:123 ccm fir
a=rtcp-fb:123 nack
a=rtcp-fb:123 nack pli
a=extmap:2 urn:ietf:params:rtp-hdrext:toffset
a=extmap:3 http://www.webrtc.org/experiments/rtp-hdrext/abs-send-time
a=extmap:4 urn:3gpp:video-orientation
a=extmap:5 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=setup:actpass
a=mid:j6gtnlva
a=msid:kREh1yv7S0I5syCOntCAIUBeMoesO6v5RlkL 28c40df0-83b8-46c7-bd06-34e7e6fc8fa0
a=sendonly
a=ice-ufrag:3lw1e76eix7edjcm
a=ice-pwd:cidqjcjfv28re4t7djaf410gkzpoblq4
a=candidate:udpcandidate 1 udp 1078862079 10.1.133.155 19211 typ host
a=end-of-candidates
a=ice-options:renomination
a=ssrc:4131643841 cname:pYEUk1YEO5F9x9T/
a=ssrc:1251779610 cname:pYEUk1YEO5F9x9T/
a=ssrc-group:FID 4131643841 1251779610
a=rtcp-mux
a=rtcp-rsize
m=audio 7 RTP/SAVPF 100
c=IN IP4 127.0.0.1
a=rtpmap:100 opus/48000/2
a=fmtp:100 minptime=10;useinbandfec=1
a=extmap:1 urn:ietf:params:rtp-hdrext:ssrc-audio-level
a=extmap:5 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=setup:actpass
a=mid:p0o0fho7
a=msid:kREh1yv7S0I5syCOntCAIUBeMoesO6v5RlkL 1271c25f-e4e8-4763-8770-2f043f426445
a=sendonly
a=ice-ufrag:3lw1e76eix7edjcm
a=ice-pwd:cidqjcjfv28re4t7djaf410gkzpoblq4
a=candidate:udpcandidate 1 udp 1078862079 10.1.133.155 19211 typ host
a=end-of-candidates
a=ice-options:renomination
a=ssrc:4125350497 cname:pYEUk1YEO5F9x9T/
a=rtcp-mux
a=rtcp-rsize
m=video 7 RTP/SAVPF 123 101
c=IN IP4 127.0.0.1
a=rtpmap:123 VP8/90000
a=rtpmap:101 rtx/90000
a=fmtp:101 apt=123
a=rtcp-fb:123 goog-remb
a=rtcp-fb:123 ccm fir
a=rtcp-fb:123 nack
a=rtcp-fb:123 nack pli
a=fmtp:123 x-google-min-bitrate=140;x-google-max-bitrate=180;x-google-start-bitrate=160;x-google-min-bitrate=140;x-google-max-bitrate=180;x-google-start-bitrate=160;x-google-min-bitrate=140;x-google-max-bitrate=180;x-google-start-bitrate=160
a=extmap:2 urn:ietf:params:rtp-hdrext:toffset
a=extmap:3 http://www.webrtc.org/experiments/rtp-hdrext/abs-send-time
a=extmap:4 urn:3gpp:video-orientation
a=extmap:5 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=setup:actpass
a=mid:i860vo1m
a=msid:nbwkpaLOrbf3snCxWpLgPCi01iwx6ghw9xu2 1098359b-2cc9-4b96-b7f4-6aa2b7c40031
a=sendonly
a=ice-ufrag:3lw1e76eix7edjcm
a=ice-pwd:cidqjcjfv28re4t7djaf410gkzpoblq4
a=candidate:udpcandidate 1 udp 1078862079 10.1.133.155 19211 typ host
a=end-of-candidates
a=ice-options:renomination
a=ssrc:2368086230 cname:QVg07Awk9yf5LedF
a=ssrc:2368086230 cname:QVg07Awk9yf5LedF
a=ssrc-group:FID 2368086230 2368086230
a=rtcp-mux
a=rtcp-rsize
m=audio 7 RTP/SAVPF 100
c=IN IP4 127.0.0.1
a=rtpmap:100 opus/48000/2
a=fmtp:100 minptime=10;useinbandfec=1
a=extmap:1 urn:ietf:params:rtp-hdrext:ssrc-audio-level
a=extmap:5 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=setup:actpass
a=mid:xwa9siz1
a=msid:nbwkpaLOrbf3snCxWpLgPCi01iwx6ghw9xu2 357db268-a530-4b09-98e9-8ad599921249
a=sendonly
a=ice-ufrag:3lw1e76eix7edjcm
a=ice-pwd:cidqjcjfv28re4t7djaf410gkzpoblq4
a=candidate:udpcandidate 1 udp 1078862079 10.1.133.155 19211 typ host
a=end-of-candidates
a=ice-options:renomination
a=ssrc:1666321053 cname:QVg07Awk9yf5LedF
a=rtcp-mux
a=rtcp-rsize

type: offer, sdp: v=0
o=mediasoup 24017464 1 IN IP4 0.0.0.0
s=-
t=0 0
a=ice-lite
a=fingerprint:sha-256 75:E9:8A:3C:96:49:89:97:18:A3:0D:73:E9:9A:59:D1:8A:B4:15:A9:8F:C4:DE:91:8F:5D:E3:73:0D:E2:00:4E
a=msid-semantic: WMS *
a=group:BUNDLE audio-tracks video-tracks
m=audio 7 RTP/SAVPF 100
c=IN IP4 127.0.0.1
a=rtpmap:100 opus/48000/2
a=fmtp:100 minptime=10;useinbandfec=1
a=extmap:1 urn:ietf:params:rtp-hdrext:ssrc-audio-level
a=setup:actpass
a=mid:audio-tracks
a=sendrecv
a=ice-ufrag:vdb6b4984o7dkf16
a=ice-pwd:4agfo1y9pl4ylg2zxrx4lufimetfuxzc
a=candidate:udpcandidate 1 udp 1078862079 10.1.133.155 51891 typ host
a=end-of-candidates
a=ice-options:renomination
a=ssrc:1689928828 cname:tw9LY2QY98p9spEm
a=ssrc:1689928828 msid:NSyf3jpXBCyhNnds6Shejy3vfxXmQRpVkcpQ 9f9624db-1c35-49a0-9898-2d578606961d
a=ssrc:2064048689 cname:0SQ2ImcTH1runIhp
a=ssrc:2064048689 msid:FWqQatBcsifPcujegGiIXt2BgBNSS89G20VC 06c7586a-c83e-4a5a-a06c-d126c49a810d
a=rtcp-mux
a=rtcp-rsize
m=video 7 RTP/SAVPF 123 101
c=IN IP4 127.0.0.1
a=rtpmap:123 VP8/90000
a=rtpmap:101 rtx/90000
a=fmtp:101 apt=123
a=rtcp-fb:123 goog-remb
a=rtcp-fb:123 ccm fir
a=rtcp-fb:123 nack
a=rtcp-fb:123 nack pli
a=fmtp:123 x-google-min-bitrate=140;x-google-max-bitrate=180;x-google-start-bitrate=160
a=extmap:2 urn:ietf:params:rtp-hdrext:toffset
a=extmap:3 http://www.webrtc.org/experiments/rtp-hdrext/abs-send-time
a=extmap:4 urn:3gpp:video-orientation
a=setup:actpass
a=mid:video-tracks
a=sendrecv
a=ice-ufrag:vdb6b4984o7dkf16
a=ice-pwd:4agfo1y9pl4ylg2zxrx4lufimetfuxzc
a=candidate:udpcandidate 1 udp 1078862079 10.1.133.155 51891 typ host
a=end-of-candidates
a=ice-options:renomination
a=ssrc:1028448819 cname:tw9LY2QY98p9spEm
a=ssrc:1028448819 msid:NSyf3jpXBCyhNnds6Shejy3vfxXmQRpVkcpQ e59b243c-f944-471b-b410-45a80db0797e
a=ssrc:788703880 cname:tw9LY2QY98p9spEm
a=ssrc:788703880 msid:NSyf3jpXBCyhNnds6Shejy3vfxXmQRpVkcpQ e59b243c-f944-471b-b410-45a80db0797e
a=ssrc:2889626611 cname:0SQ2ImcTH1runIhp
a=ssrc:2889626611 msid:FWqQatBcsifPcujegGiIXt2BgBNSS89G20VC c73ef760-4a91-4077-9bf1-fbdda5c10c71
a=ssrc:4061195486 cname:0SQ2ImcTH1runIhp
a=ssrc:4061195486 msid:FWqQatBcsifPcujegGiIXt2BgBNSS89G20VC c73ef760-4a91-4077-9bf1-fbdda5c10c71
a=ssrc-group:FID 1028448819 788703880
a=ssrc-group:FID 2889626611 4061195486
a=rtcp-mux
a=rtcp-rsize