[Live-devel] redundant RTP stream setup question

[Ross Finlayson]

> I am working on a system having 2 redundant streamers. The slave streamer starts streaming when a failure is detected on the primary streamer.

Unfortunately, the problem with what you're trying to do is that separate RTP multicast streams - even if sent to the same multicast address+port, using the same RTP payload format (i.e., codec) - are independent.  They have different "SSRC" fields, and, more importantly, different (initially randomized) RTP timestamp values.  A receiver that was previously receiving the 'primary' stream won't be able to properly handle the 'backup' stream, even if there's no overlap between the two streams, UNLESS it explicitly knows about the fact that it needs to stop receiving the 'primary' stream, and start receiving the 'backup' stream:

> Players (VLC using live555 (v2014.05.27)) are notified of the change with SAP.

OK, this gives you the opportunity to do the right thing.  Your player - once it learns about the new stream - can stop receiving the existing stream (i.e., by closing "RTPSource" and "groupsock" objects, etc.), and then start receiving the new stream (by creating new "groupsock" and "RTPSource" objects, etc.).  If you do this, then I suggest using a completely different multicast address+port for the 'backup' stream (you can do this because you're announcing it via SAP).  Then you won't have any problem with overlap between the two streams.


Ross Finlayson
Live Networks, Inc.
http://www.live555.com/

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