[Ffmpeg-devel] udp multicast?

Ronald S. Bultje rbultje
Mon Mar 12 00:12:59 CET 2007


I've briefly looked at the possibility of supporting Windows Media
Stations (those ~base64-encoded .nsc files that were in the news 1-2 yrs
ago). They appear to contain an IP address in the multicast support
range, a port on that IP to connect to, sometimes a fallback unicast url
and a multicast adapter IP (outside the multicast range - this is
presumably the multicast source?) + some other trash (format/description
is most likely to choose a specific bitrate, similar to mms, so I'm
ignoring that for now).

However, even though udp.c supports multicast, connecting to
udp://ip.ip.ip.ip:port,multicast=%d,ttl=%d doesn't do much (hangs in
url_read() never getting any data). The fact that udp.c contains
multicast code most likely means it was tested in some setting. How was
this tested, how do I get a test setting using this to work? I'd like to
play with it and see if I can get any data out of it.

(Which reminds me, so if I connect to a multicast IP in the middle, how
does this server know that I want data from radiostation X rather than
hacknetwork Y, porn network Z or radiostation A? Or is multicast set up
in a per-host fashion where the first client connects directly to the
source and each multicast-capable router in between is automatically
converted into a multicast router "source" for future connecting
clients? If so, how does the original source know the IP of the
multicast-router closest to me? Or is this way more automagic than what
I'm imagining here, where I'd just "connect" to the source IP and
routers in between would do everything automagically and am I totally
missing the point? If that's the case, then why are there multicast IP

<I-don't-get-it-yet/> :-)


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