All things related to multicast

["Marshall Eubanks" <>]

On Thu, 21 Mar 2002 15:01:20 EST
 Alan Crosswell 
<>
 wrote:
> >vBrick offers their propriatary system streams in
> addition
> >to rtp, which has very good synchronization, but
> requires
> >their propriatary player.
> 
> How come I can watch CSPAN from Northwestern using IPTV
> viewer?  It appears
> to be coming as Vbrick's UDP stream (to a single
> multicast group as raw
> UDP).

All multicasts are UDP. 
The CSPAN multicasts are elementary streams (i.e., separate
streams for audio and video) multicast over RTP over UDP.

Most any video you see in sdp is done the same way (maybe
with a different protocol).

The AVT working group at the IETF has never formalized a 
system stream for MPEG-1/2 over RTP.

The trouble with elementary streams is, as the audio and
video are separate,it is not easy to guarantee that the
streams stay in sync.

In the system stream, the audio and video are multiplexed
together, so the (non-RTP, but UDP) vBrick system stream
multicasts do a much better job, at the cost of requiring
the vBrick player.

The same situation applies in MPEG-4. Our test MPEG-4 
streams at
http://www.multicasttech.com/otv/
are elementary streams, although in this case the sync seems
pretty good.

The AVT group in the IETF is working to define a system
stream RFC for MPEG-4 eventually, but has no plans at
present to do
this for mpeg-1/2.

Regards
Marshall

> 
> Joel must be out of town as I sent him mail asking how he
> configured
> his but received no reply.
> /a
>