Re: [rtcweb] SDP and ssrc-group,
Iñaki Baz Castillo <ibc@aliax.net> Tue, 21 October 2014 17:40 UTC
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Date: Tue, 21 Oct 2014 19:40:46 +0200
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From: Iñaki Baz Castillo <ibc@aliax.net>
To: Peter Thatcher <pthatcher@google.com>
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Cc: rtcweb@ietf.org
Subject: Re: [rtcweb] SDP and ssrc-group,
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How is that? Where is that specified? What about if I include 3 ssrc values in the ssrc-group? What is each one for? On 21 Oct 2014 19:31, "Peter Thatcher" <pthatcher@google.com> wrote: > 345259865 is "real" > 2693756249 is rtx > > On Tue, Oct 21, 2014 at 9:25 AM, Iñaki Baz Castillo <ibc@aliax.net> wrote: > >> Hi, >> >> May I know which SSRC (345259865 or 2693756249) will be used for the >> real media stream (plus RED and FEC) and which SSRC will be used for >> RTX? >> >> >> >> -------------------------- >> m=video 62164 RTP/SAVPF 100 116 117 96 >> a=mid:video >> a=rtpmap:100 VP8/90000 >> a=rtpmap:116 red/90000 >> a=rtpmap:117 ulpfec/90000 >> a=rtpmap:96 rtx/90000 >> a=fmtp:96 apt=100 >> a=ssrc-group:FID 345259865 2693756249 >> a=ssrc:345259865 cname:erS7E/KHLYKTejNs >> a=ssrc:345259865 msid:DWpWct9bWKzTMNYZn5bKVgwZ8Mfy2EtfqBY5 >> c0134f05-e7c2-4afd-a979-4e224de5eb91 >> a=ssrc:345259865 mslabel:DWpWct9bWKzTMNYZn5bKVgwZ8Mfy2EtfqBY5 >> a=ssrc:345259865 label:c0134f05-e7c2-4afd-a979-4e224de5eb91 >> a=ssrc:2693756249 cname:erS7E/KHLYKTejNs >> a=ssrc:2693756249 msid:DWpWct9bWKzTMNYZn5bKVgwZ8Mfy2EtfqBY5 >> c0134f05-e7c2-4afd-a979-4e224de5eb91 >> a=ssrc:2693756249 mslabel:DWpWct9bWKzTMNYZn5bKVgwZ8Mfy2EtfqBY5 >> a=ssrc:2693756249 label:c0134f05-e7c2-4afd-a979-4e224de5eb91 >> ------------------------------- >> >> >> >> >> RFC 5576 does not clarify it at all: >> >> http://tools.ietf.org/html/rfc5576#section-4.2 >> >> -------------------------------------------------- >> 4.2. The "ssrc-group" Media Attribute >> >> a=ssrc-group:<semantics> <ssrc-id> ... >> >> [..] >> >> The <semantics> parameter is taken from the specification of the >> "group" attribute [RFC3388]. The initial semantic values defined for >> the "ssrc-group" attribute are FID (Flow Identification) [RFC3388] >> and FEC (Forward Error Correction) [RFC4756]. In each case, the >> relationship among the grouped sources is the same as the >> relationship among corresponding sources in media streams grouped >> using the SDP "group" attribute. >> -------------------------------------------------- >> >> >> >> The referenced RFC 3388 neither clarifies it: >> >> --------------------------------------------------- >> 7.4 FID Semantics >> >> Several "m" lines grouped together using FID semantics form a media >> flow. A media agent handling a media flow that comprises several "m" >> lines MUST send a copy of the media to every "m" line part of the >> flow as long as the codecs and the direction attribute present in a >> particular "m" line allow it. >> >> It is assumed that the application uses only one codec at a time to >> encode the media produced. This codec MAY change dynamically during >> the session, but at any particular moment only one codec is in use. >> >> The application encodes the media using the current codec and checks >> one by one all the "m" lines that are part of the flow. If a >> particular "m" line contains the codec being used and the direction >> attribute is "sendonly" or "sendrecv", a copy of the encoded media is >> sent to the address/port specified in that particular media stream. >> If either the "m" line does not contain the codec being used or the >> direction attribute is neither "sendonly" nor "sendrecv", nothing is >> sent over this media stream. >> ---------------------------------------------------- >> >> >> >> >> So, how is the usage of ssrc-group? Where is it really defined? >> >> Can I put more than 2 ssrc together in the same ssrc-group line? >> >> How should the receiver interpret it? >> >> Does a ssrc-group always mean RTX usage? Where is that specified in >> the above SDP? >> >> Does not the above SDP look a complete mixture of hacks and workarounds? >> >> >> >> >> -- >> Iñaki Baz Castillo >> <ibc@aliax.net> >> >> _______________________________________________ >> rtcweb mailing list >> rtcweb@ietf.org >> https://www.ietf.org/mailman/listinfo/rtcweb >> > >
- [rtcweb] SDP and ssrc-group, Iñaki Baz Castillo
- Re: [rtcweb] SDP and ssrc-group, Peter Thatcher
- Re: [rtcweb] SDP and ssrc-group, Iñaki Baz Castillo
- Re: [rtcweb] SDP and ssrc-group, Peter Thatcher
- Re: [rtcweb] SDP and ssrc-group, Bernard Aboba
- Re: [rtcweb] SDP and ssrc-group, Sergio Garcia Murillo
- Re: [rtcweb] SDP and ssrc-group, Iñaki Baz Castillo
- Re: [rtcweb] SDP and ssrc-group, Justin Uberti
- Re: [rtcweb] SDP and ssrc-group, Makaraju, Maridi Raju (Raju)
- Re: [rtcweb] SDP and ssrc-group, Sergio Garcia Murillo
- Re: [rtcweb] SDP and ssrc-group, Iñaki Baz Castillo
- Re: [rtcweb] SDP and ssrc-group, Makaraju, Maridi Raju (Raju)
- Re: [rtcweb] SDP and ssrc-group, Sergio Garcia Murillo
- Re: [rtcweb] SDP and ssrc-group, Makaraju, Maridi Raju (Raju)
- Re: [rtcweb] SDP and ssrc-group, Bernard Aboba
- Re: [rtcweb] SDP and ssrc-group, Suhas Nandakumar
- Re: [rtcweb] SDP and ssrc-group, Bernard Aboba
- Re: [rtcweb] SDP and ssrc-group, Sergio Garcia Murillo
- Re: [rtcweb] SDP and ssrc-group, Sergio Garcia Murillo
- Re: [rtcweb] SDP and ssrc-group, Peter Thatcher
- Re: [rtcweb] SDP and ssrc-group, Makaraju, Maridi Raju (Raju)
- Re: [rtcweb] SDP and ssrc-group, Makaraju, Maridi Raju (Raju)
- Re: [rtcweb] SDP and ssrc-group, Bernard Aboba
- Re: [rtcweb] SDP and ssrc-group, Makaraju, Maridi Raju (Raju)
- Re: [rtcweb] SDP and ssrc-group, Timothy B. Terriberry
- Re: [rtcweb] SDP and ssrc-group, Sergio Garcia Murillo
- Re: [rtcweb] SDP and ssrc-group, Makaraju, Maridi Raju (Raju)
- Re: [rtcweb] SDP and ssrc-group, Timothy B. Terriberry
- Re: [rtcweb] SDP and ssrc-group, Timothy B. Terriberry
- Re: [rtcweb] SDP and ssrc-group, Makaraju, Maridi Raju (Raju)
- Re: [rtcweb] SDP and ssrc-group, Justin Uberti
- Re: [rtcweb] SDP and ssrc-group, Martin Thomson
- Re: [rtcweb] SDP and ssrc-group, Mo Zanaty (mzanaty)
- Re: [rtcweb] SDP and ssrc-group, Bernard Aboba
- Re: [rtcweb] SDP and ssrc-group, Christer Holmberg
- Re: [rtcweb] SDP and ssrc-group, Roni Even
- Re: [rtcweb] SDP and ssrc-group, Sergio Garcia Murillo
- Re: [rtcweb] SDP and ssrc-group, Makaraju, Maridi Raju (Raju)
- Re: [rtcweb] SDP and ssrc-group, Sergio Garcia Murillo
- Re: [rtcweb] SDP and ssrc-group, Roni Even
- Re: [rtcweb] SDP and ssrc-group, Sergio Garcia Murillo
- Re: [rtcweb] SDP and ssrc-group, Justin Uberti