[FFmpeg-devel] [PATCH v2] avformat: enable UDP IPv6 multicast interface selection

[Rémi Denis-Courmont]

Le torstaina 21. maaliskuuta 2024, 15.01.09 EET Ignjatović, Lazar (RS) a écrit 
:
> > Your MR makes even less sense for multicast. For multicast there is no
> > local address to match to an interface. So you just have to have the
> > interface specified explicitly in addition to the LL group address. This
> > is true for both egress and ingress.
> 
> I've compared ffmpeg 5.1.2 against my MR on IPv6 multicast. Here are the
> results:

I don't care. That does not make your MR any less counter-sensical.

If you could infer the scope ID from the IPv6 address, there wouldn't be a 
scope ID field in the socket address in the first place. Is it that hard to 
understand?

If you tests show anything, it's that LL addressing is not intended for 
application protocols. This is consistent with the fact that nobody cared to 
support this combination in FFmpeg after 28 years of IPv6. Now I don't mind 
adding proper support, but not kludges.

> So the problem to overcome here is controlling on which interface we
> listen/send multicat IPv6.

That "problem" was solved before FFmpeg existed by adding a separate parameter 
(ping6) or prepending the interface name after a percent sign (glibc).

-- 
Rémi Denis-Courmont
http://www.remlab.net/