Bug 195878

Summary: RTCPeerConnection: removeTrack() renders subsequent addTrack() ineffective
Product: WebKit Reporter: Arne Gleditsch <argggh>
Component: WebRTCAssignee: Nobody <webkit-unassigned>
Status: RESOLVED CONFIGURATION CHANGED    
Severity: Normal CC: ben.browitt, youennf
Priority: P2    
Version: Safari Technology Preview   
Hardware: Mac   
OS: macOS 10.14   

Description Arne Gleditsch 2019-03-18 02:42:10 PDT 
The offer sdp produced by RTCPeerConnection in Safari TP77 shows odd behavior when Plan B signalling is selected. The code at https://codepen.io/argggh/pen/ywEoLE, which essentially does ``addTrack(s1); removeTrack(addTrack(s2)); addTrack(s3);`` seems to never include information about the last track in the SDP produced by createOffer(). 

With Develop > Experimental Features > WebRTC Unified Plan enabled, the output looks like this:

    Tracks
    e5f95eb8-3431-47ec-b1fe-268500fccf81 / b207958a-16c9-435f-8054-04fb836bcfdb
    77de217a-af19-429f-8132-a4b3d858d27f / 3c4241fb-d540-484c-aea9-7795e8c1f91d
    c4625cbd-5e95-410c-ac26-e09ebc1d43e5 / 514367c2-0479-403d-9a06-3f81c7b7ad60

    SDP (add tracks 1 and 2)
    a=msid:e5f95eb8-3431-47ec-b1fe-268500fccf81 b207958a-16c9-435f-8054-04fb836bcfdb
    a=ssrc:3363836655 msid:e5f95eb8-3431-47ec-b1fe-268500fccf81 b207958a-16c9-435f-8054-04fb836bcfdb
    a=ssrc:2717606554 msid:e5f95eb8-3431-47ec-b1fe-268500fccf81 b207958a-16c9-435f-8054-04fb836bcfdb
    a=msid:77de217a-af19-429f-8132-a4b3d858d27f 3c4241fb-d540-484c-aea9-7795e8c1f91d
    a=ssrc:2879751916 msid:77de217a-af19-429f-8132-a4b3d858d27f 3c4241fb-d540-484c-aea9-7795e8c1f91d
    a=ssrc:2516360126 msid:77de217a-af19-429f-8132-a4b3d858d27f 3c4241fb-d540-484c-aea9-7795e8c1f91d

    SDP (remove track 2, add track 3)
    a=msid:e5f95eb8-3431-47ec-b1fe-268500fccf81 b207958a-16c9-435f-8054-04fb836bcfdb
    a=ssrc:1595518495 msid:e5f95eb8-3431-47ec-b1fe-268500fccf81 b207958a-16c9-435f-8054-04fb836bcfdb
    a=ssrc:1184215358 msid:e5f95eb8-3431-47ec-b1fe-268500fccf81 b207958a-16c9-435f-8054-04fb836bcfdb
    a=msid:c4625cbd-5e95-410c-ac26-e09ebc1d43e5 3c4241fb-d540-484c-aea9-7795e8c1f91d
    a=ssrc:3057393757 msid:c4625cbd-5e95-410c-ac26-e09ebc1d43e5 3c4241fb-d540-484c-aea9-7795e8c1f91d
    a=ssrc:3665793179 msid:c4625cbd-5e95-410c-ac26-e09ebc1d43e5 3c4241fb-d540-484c-aea9-7795e8c1f91d

however, when the Unified Plan is disabled, this is the result:

    Tracks
    12c56731-3e2d-4963-bf5c-aba54937cc26 / df2d5416-947b-4475-b0a4-a0d85fae51cf
    f8efb466-b232-437d-99fd-660632b21f15 / 171ff4e9-04ef-48f4-ab71-59644068ba25
    e56c1adb-e5bb-4dc6-87fd-1d154d90b1dd / f71f1a2a-ccf8-4f50-aa12-e99760b5f57f

    SDP (add tracks 1 and 2)
    a=ssrc:3446938118 msid:12c56731-3e2d-4963-bf5c-aba54937cc26 df2d5416-947b-4475-b0a4-a0d85fae51cf
    a=ssrc:3574411983 msid:12c56731-3e2d-4963-bf5c-aba54937cc26 df2d5416-947b-4475-b0a4-a0d85fae51cf
    a=ssrc:2997856108 msid:f8efb466-b232-437d-99fd-660632b21f15 171ff4e9-04ef-48f4-ab71-59644068ba25
    a=ssrc:3685245765 msid:f8efb466-b232-437d-99fd-660632b21f15 171ff4e9-04ef-48f4-ab71-59644068ba25

    SDP (remove track 2, add track 3)
    a=ssrc:304486373 msid:12c56731-3e2d-4963-bf5c-aba54937cc26 df2d5416-947b-4475-b0a4-a0d85fae51cf
    a=ssrc:297767829 msid:12c56731-3e2d-4963-bf5c-aba54937cc26 df2d5416-947b-4475-b0a4-a0d85fae51cf

As can be seen, track 3 is not mentioned in the offer SDP at all.
Comment 1 Ben 2019-05-02 03:23:51 PDT 
Arne did you find a workaround to make the third track show in the SDP?
Comment 2 youenn fablet 2019-06-07 14:06:55 PDT 
This should be fixed now that unified plan is on.