Re: [rtcweb] No Plan - SDP offer/answer clarification
"Roni Even" <ron.even.tlv@gmail.com> Tue, 04 June 2013 21:54 UTC
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From: Roni Even <ron.even.tlv@gmail.com>
To: 'Bernard Aboba' <bernard_aboba@hotmail.com>
References: <020e01ce6045$4b07dee0$e1179ca0$@gmail.com> <51AC73EE.5080603@jitsi.org> <026201ce60a6$6d406f20$47c14d60$@gmail.com> <BLU404-EAS14250610902587788E9538F939E0@phx.gbl>
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Date: Wed, 05 Jun 2013 00:52:43 +0300
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Cc: rtcweb@ietf.org
Subject: Re: [rtcweb] No Plan - SDP offer/answer clarification
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Hi, It is a question about what de-multiplexing means. When I think about multiplexing it means directing an RTP stream to a decoder (can be a DSP for each RTP video stream that does both RTP and video decoding) so the de-multiplexing is based not only on pt but also on SSRC but you do not need to know the SSRC in the SDP. Roni > -----Original Message----- > From: Bernard Aboba [mailto:bernard_aboba@hotmail.com] > Sent: 04 June, 2013 8:30 PM > To: Roni Even > Cc: Emil Ivov; rtcweb@ietf.org > Subject: Re: [rtcweb] No Plan - SDP offer/answer clarification > > No. It just means that you cannot have two different codecs with the same > PT on the same m line (without Bundle) or in any m-line (with Bundle). > > On Jun 3, 2013, at 3:11 PM, "Roni Even" <ron.even.tlv@gmail.com> wrote: > > > Hi Emil, > > My understanding is that you propose to de-multiplex by the pt number > > so you cannot have two rtp streams with the same payload type number > > Roni > > > >> -----Original Message----- > >> From: Emil Ivov [mailto:emcho@jitsi.org] > >> Sent: 03 June, 2013 1:46 PM > >> To: Roni Even > >> Cc: rtcweb@ietf.org > >> Subject: Re: [rtcweb] No Plan - SDP offer/answer clarification > >> > >> Hey Roni, > >> > >> On 03.06.13, 13:29, Roni Even wrote: > >>> Hi, > >>> I read the draft and the email thread and I think I have similar > >>> questions to the ones Cullen made. > >>> My understanding was that the proposal is to do one SDP offer/ > >>> answer exchange and add remove streams using other means (not > >>> specified) > >> > >> Yes, this is exactly it. > >> > >>> I looked at the offer example is section 3 and it has > >>> > >>> a=max-send-ssrc:{*:1} // declaring maximum > >>> a=max-recv-ssrc:{*:4} // number of SSRCs > >>> > >>> I have some clarifying questions? > >>> > >>> 1. Is the proposal to always offer max-send-ssrc=1? > >>> > >>> 2. What is the answer in this case can it be max-send-ssrc=4? > >> > >> The max-ssrc in the SDP was just an example for capabilities that the > > offerer > >> could add to SDP (could be useful for mobile devices for example). It > >> is > > by no > >> means essential to the approach. > >> > >>> 3. If max-send-ssrc >1 in the answer and the m-line has, for > >>> example, support for H.264 and VP8 with max-send-ssrc=2 and > >>> de-multiplexing is based on pt number, it will require four pt in > >>> the m-line since there can be two > >>> VP8 or two H.264 RTP streams > >>> > >>> m=video 5002 RTP/SAVPF 97 98 99 100 > >>> a=mid:video > >>> a=rtcp-mux > >>> a=rtpmap:97 VP8/90000 > >>> a=rtpmap:98 VP8/90000 > >>> a=rtpmap:99 H264/90000 > >>> a=rtpmap:100 H264/90000 > >>> Is my understanding correct? > >> > >> Can you help me understand why you need the PT duplication? Is this > >> just > > so > >> that you could understand distinguish between two sources? If so, > >> then it wouldn't be necessary. > >> > >> With No Plan you would just send: > >> > >> m=video 5002 RTP/SAVPF 97 99 > >> a=mid:video > >> a=rtcp-mux > >> a=rtpmap:97 VP8/90000 > >> a=rtpmap:99 H264/90000 > >> > >> If then you want to have one of the VP8 streams rendered on the left > > screen > >> and the other on the right, you will add this in application-specific > > signalling. A > >> web application could do this like this: > >> > >> { > >> "leftSSRC": "1234", > >> "rightSSRC": "5678" > >> } > >> > >> An WebRTC-to-SIP gateway could transform this into SDP or whatever > >> that target devices need. > >> > >> Does this answer your question? > >> > >> Emil > >> > >> > >> > >>> > >>> > >>> Roni > >>> > >>> > >>> > >>>> -----Original Message----- > >>>> From: rtcweb-bounces@ietf.org [mailto:rtcweb-bounces@ietf.org] On > >>>> Behalf Of Emil Ivov > >>>> Sent: 29 May, 2013 10:00 PM > >>>> To: rtcweb@ietf.org > >>>> Subject: [rtcweb] No Plan > >>>> > >>>> Hey all, > >>>> > >>>> Based on many of the discussions that we've had here, as well as > >>>> many others that we've had offlist, it seemed like a good idea to > > investigate a > >>>> negotiation alternative that relies on SDP and Offer/Answer just a > > little > >>> bit > >>>> less. > >>>> > >>>> The following "no plan" draft attempts to present one such approach: > >>>> > >>>> http://tools.ietf.org/html/draft-ivov-rtcweb-noplan > >>>> > >>>> The draft relies on conventional use of SDP O/A but leaves the > > intricacies > >>> of > >>>> multi-source scenarios to application-specific signalling, with > >>> potentially a > >>>> little help from RTP. > >>>> > >>>> Hopefully, proponents of Plans A and B would find that the > >>> interoperability > >>>> requirements that concerned them can still be met with "no plan". > >>>> Of > >>> course > >>>> they would have to be addressed by application-specific signalling > > and/or > >>>> signalling gateways. > >>>> > >>>> Comments are welcome! > >>>> > >>>> Cheers, > >>>> Emil > >>>> > >>>> -- > >>>> https://jitsi.org > >>>> _______________________________________________ > >>>> rtcweb mailing list > >>>> rtcweb@ietf.org > >>>> https://www.ietf.org/mailman/listinfo/rtcweb > >> > >> -- > >> https://jitsi.org > > > > _______________________________________________ > > rtcweb mailing list > > rtcweb@ietf.org > > https://www.ietf.org/mailman/listinfo/rtcweb
- Re: [rtcweb] No Plan - SDP offer/answer clarifica… Roni Even
- Re: [rtcweb] No Plan - SDP offer/answer clarifica… Emil Ivov
- Re: [rtcweb] No Plan - SDP offer/answer clarifica… Emil Ivov
- Re: [rtcweb] No Plan - SDP offer/answer clarifica… Roni Even
- Re: [rtcweb] No Plan - SDP offer/answer clarifica… Emil Ivov
- Re: [rtcweb] No Plan - SDP offer/answer clarifica… Roni Even
- Re: [rtcweb] No Plan - SDP offer/answer clarifica… Bernard Aboba
- Re: [rtcweb] No Plan - SDP offer/answer clarifica… Roni Even
- Re: [rtcweb] No Plan - SDP offer/answer clarifica… Mary Barnes