[vlc-devel] [PATCH] live555: fix the subtitles issue

Rémi Denis-Courmont remi at remlab.net
Mon Dec 30 15:08:04 CET 2013

Le lundi 30 décembre 2013, 14:57:40 Gilles Chanteperdrix a écrit :
> Do you know how NAT traversal works for any UDP connection, like e.g.
> DNS requests?

Yes and that is entirely different from RTP.

> I am doing the same thing.

You cannot do the "same thing". DNS is a request/response protocol. The client 
does not need to know its outer source address and port pair. Futhermore, the 
NAT flow only lasts a few seconds at most. until one packet is received.

RTP is completely different.

> It requires a little modification of the client,

No. Changing the client will not help. Only the NAT and the server knows the 
outer address and port pair. While you can just tell the server to reuse the 
same address as that of the TCP connection, you are still left guessing the 
UDP port number for the SETUP request.

> which is already implemented in live555 and ffmpeg, because it
> seems to be required even if the firewall has ALG.

No. If the firewall has a working RTSP ALG, you don't need to punch holes, by 

> And a modification of the server to use that supplementary information sent
> by the client.

Then it is no longer RTSP but some non-standard and non-interoperable dialect 
of RTSP. Your "enhanced" client will not work while talking with a plain 
standard server.

> the server can still obey the standard if it does not receive the
> information.

In other words, NAT traversal does not work without cooperation from the 
server. That's exactly what I said. You are contradicting your own self.

Rémi Denis-Courmont

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