[FFmpeg-devel] url_fopen creates IPv6 socket for url "rtp://localhost:XXX"

Martin Storsjö martin
Fri Aug 13 15:41:25 CEST 2010


On Fri, 13 Aug 2010, Dominik Tomczak wrote:

> On Windows 7 Home Premium while using libavformat and opening url 
> "rtp://localhost:XXXX" (XXXX is a port number) I can see that 2 UDP 
> sockets are created but both are IPv6, not IPv4. Does anybody know why? 
> I haven't specified IPv6 in URL. Is IPv6 a default IP version in FFMpeg 
> on Windows 7?

You haven't specified anything IPv4-specific either. localhost resolves to 
both (for IPv4) and ::1 (for IPv6) and we choose the one the OS 
returns first, which is out of our control. If you want to be sure of 
which one you get, specify a numeric IP.

For connection-oriented protocols that use TCP, we try connecting on all 
of them, one at a time, but for UDP, we can't really know which one the 
user wants.

So when in doubt, use a numerical IP with everything UDP-based.

// Martin

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