udpsrc multicast sockets ignoring multicast IP

[Nicolas Dufresne]

Le mercredi 25 septembre 2019 à 09:15 -0500, Tim a écrit :
> Hi all,
> 
> In previous posts I've described behavior where we have a multicast pipeline
> using rtspsrc.  We have multiple pipelines running in a single process to be
> able to record video/audio from multiple sources.  We noted that frequently
> we are seeing SSRC value changes in the RTP session that did not come from
> the video/audio source and were trying to understand how that could have
> happened.
> 
> It turns out that our video/audio sources are using different multicast IP
> addresses per source, but all using the same port for their audio RTP stream
> and all using the same port for the video RTP stream (e.g. source 1 using IP
> address A and port X for video and Y for audio and source 2 using IP address
> B and port X for video and Y for audio).  From all of my reading this should
> not be a problem, but we are seeing the sockets for each pipeline picking up
> RTP payloads from others causing the SSRC change, upstream pad creation,
> etc.  Making each video source and audio source use a unique port number
> resolved the issue.
> 
> Should udpsrc be using IP address/port combo during socket creation?

Multicast registration is system wide, so in many cases, all socket
receives packets from random stream. We have code that drop the
irrelevant packets, though I don't know enough of the details to
explain why things don't get filtered out properly for you case.

> 
> Thank you for all of your help.
> 
> -Tim
> 
> 
> 
> 
> 
> --
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