Re: [MMUSIC] FW: [rtcweb] How to signal RTX SSRCs with simulcast

Iñaki Baz Castillo <ibc@aliax.net> Mon, 13 March 2017 10:46 UTC

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From: =?UTF-8?Q?I=C3=B1aki_Baz_Castillo?= <ibc@aliax.net>
Date: Mon, 13 Mar 2017 11:46:01 +0100
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To: Bo Burman <bo.burman@ericsson.com>
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Subject: Re: [MMUSIC] FW: [rtcweb] How to signal RTX SSRCs with simulcast
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2017-03-13 10:56 GMT+01:00 Bo Burman <bo.burman@ericsson.com>om>:
> I’m personally slightly inclined to suggest always using RepairedRtpStreamId
> in the rtx redundancy RTP stream to relate it to the original RTP stream
> (second “if” bullet above), mainly to avoid having to change interpretation
> of RtpStreamId based on the optional presence of RepairedRtpStreamId. I’m of
> course open to arguments.

Personally I prefer option A (use a shared RtpStreamId). My rationale:

If we go with option B (RepairedRtpStreamId) then we will need
something similar when it comes to FLEX-FEC [*]:

        v=0
        o=ali 1122334455 1122334466 IN IP4 fec.example.com
        s=2-D Parity FEC with no in band signalling Example
        t=0 0
        m=video 30000 RTP/AVP 100 110
        c=IN IP4 233.252.0.1/127
        a=rtpmap:100 MP2T/90000
        a=rtpmap:110 flexfec/90000
        a=fmtp:110 L:5; D:10; ToP:2; repair-window:200000
        a=ssrc:1234
        a=ssrc:2345
        a=ssrc-group:FEC-FR 1234 2345


For me it's to think in RtpStreamId as "the identificator of a media
stream and, optionally, also the identificator of the RTX stream and
FEC stream of such a media stream".



[*] https://tools.ietf.org/html/draft-ietf-payload-flexible-fec-scheme-03


-- 
Iñaki Baz Castillo
<ibc@aliax.net>