[OpenSIPS-Users] MediaProxy - capture or otherwise manipulate RTP packets

Stylianos Papanastasiou stylianos at gmail.com
Tue Feb 22 11:43:08 CET 2011


I have been trying to understand the workings of the MediaProxy with respect
to forwarding packets in the context of OpenSips. The accompanying
documentation and mailing list articles have been clear enough to get me to
the point where I can use MediaProxy to relay traffic between two NATed
terminals. Now, I am trying to record and/or otherwise manipulate the RTP
packets in the conversation  between two users.

As I understand it MediaProxy uses the Linux kernel's Netfilter and
conntrack to forward and monitor traffic between two endpoints. However, I
am not quite sure how to intercept an RTP packet coming from one endpoint to
the relay, then capture and/or modify it, and then forward it on its
destination. I initially thought that the C functions in _conntrack.c would
provide a clue but this has lead me nowhere. Then it would seem that
the  def check_create_conntrack(self) function in mediacontrol.py could be
the place where forwarding functions could be written - alas I am still not

I was wondering if someone more knowledgeable than I could provide some
insight into this. Eventually I would like to record and manipulate RTP
packets per connection pair and a "quick and dirty" hack suggestion would be
more than welcome for my purposes at this stage. I realise that my inquiry
is quite broad but I would really appreciate any insight I can get. I have
searched the mailing list exhaustively for this and have found several red
herrings but no real clues.

Thanks to everyone for reading this, I hope someone out there can offer some

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