[vlc] Re: Several multicast sources on a single group

[Ross Finlayson]

Some of the answers to the original question have been 
confused.  Source-specific multicast (SSM) and IGMPv3 are irrelevant 
here.  The original poster was *not* asking how to receive multicast 
streams where non-valid senders have (accidentally or maliciously) been 
injecting bogus multicast packets.  Instead, he was asking about receiving 
multicast sessions where more than one sender *legitimately* sends to the 
same multicast group - e.g., multicast conference sessions with more than 
one concurrent speaker, or more than one video source  (e.g., the MBone 
"Places All Over the World" session).

John Anderson asked:
>Could you explain the problem a little better?  If you have two streams
>broadcasting on the same MC group with the same port then it should be
>expected that the streams will mix.  How would you distinguish between the
>two sources?

You would distinguish between the two sources by the RTP "SSRC" 
(synchronization source) field, which would differ for each source.

To handle streams like this, two things would need to be done:
1/ The LIVE.COM library code would need to be updated to support 
demultiplexing an input RTP stream based on SSRC.  (At present it delivers 
a single RTP stream to callers, regardless of the SSRC.)  There will also 
need to be some mechanism for 'triggering' a new handler function whenever 
a new SSRC is seen - e.g., when a new video source appears.
2/ The VLC code will need to be updated to support the creation of multiple 
video windows - one for each video source.  (Note: For compability with the 
LIVE.COM code, these multiple video windows should *not* use separate threads.)

If support for 2/ is added to VLC, I can take a crack at task 1/.  Just let 
me know...


	Ross Finlayson
	LIVE.COM
	<http://www.live.com/>

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