Re: [FFmpeg-devel] [PATCH] avformat/rtpproto: add support for RTP/UDP socket reuse

[Camille Oudot <camille+ffmpeg-devel@voila.events>]

Why does the "reuse" option exists on the "udp" protocol in the first
place? Why would it not apply to "rtp" also?

Here is the original patch proposal on udp:
http://ffmpeg.org/pipermail/ffmpeg-devel/2006-October/thread.html#18946

> Sure. But then that does not solve the problem of RTCP mux and SDP
> bundle, which normally would use the exact same IP address and port
> number on the local end (and also on the far end, if set).

I confirm the requirement is to send several RTP streams with FFmpeg
with identical proto/src_ip/src_port/dst_ip/dst_port.

> > 
> It's not that simple. The semantics of REUSEPORT varies between Linux
> and BSD. IIRC, REUSEPORT was originally meant by BSD to allow
> multiple processes to listen on the same multicast group, but then
> Linux redefined it with radically different semantics, for receive
> load-balancing purpose.

They added SO_REUSEPORT_LB in BSD to mimic the Linux behavior.

> 
> Repeating myself, but I don't see how that solves the problem. You
> don't need REUSEADDR for two sockets to send to the same remote
> IP/port, and you cannot rely on it to send from the same local
> IP/port.

It *does* work, at least on Linux: I can send several RTP streams from
the exact same local IP/port (and _to_ the same IP/port too but that's
not a problem in general as you point it) with either REUSEADDR or
REUSEPORT options set.

Here are ffmpeg strace traces for local RTCP port == local RTP port.
The command sends a video stream to the following RTP URL (RTP and are
sent from the same local source port):

rtp://127.0.0.1:40000?localaddr=127.0.0.1&localport=22300&localrtcpport
=22300&rtcpport=40000

without SO_REUSEPORT
====================
...
socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC, IPPROTO_IP) = 4
bind(4, {sa_family=AF_INET, sin_port=htons(22300),
    sin_addr=inet_addr("127.0.0.1")}, 16) = 0
getsockname(4, {sa_family=AF_INET, sin_port=htons(22300),
    in_addr=inet_addr("127.0.0.1")}, [128->16]) = 0
setsockopt(4, SOL_SOCKET, SO_SNDBUF, [32768], 4) = 0
socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC, IPPROTO_IP) = 5
bind(5, {sa_family=AF_INET, sin_port=htons(22300),
    in_addr=inet_addr("127.0.0.1")}, 16) = -1 EADDRINUSE (Address
    already in use)

with SO_REUSEPORT
=================
...
socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC, IPPROTO_IP) = 4
setsockopt(4, SOL_SOCKET, SO_REUSEPORT, [1], 4) = 0
bind(4, {sa_family=AF_INET, sin_port=htons(22300),
    sin_addr=inet_addr("127.0.0.1")}, 16) = 0
getsockname(4, {sa_family=AF_INET, sin_port=htons(22300),
sin_addr=inet_addr("127.0.0.1")}, [128->16]) = 0
setsockopt(4, SOL_SOCKET, SO_SNDBUF, [32768], 4) = 0
socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC, IPPROTO_IP) = 5
setsockopt(5, SOL_SOCKET, SO_REUSEPORT, [1], 4) = 0
bind(5, {sa_family=AF_INET, sin_port=htons(22300),
    sin_addr=inet_addr("127.0.0.1")}, 16) = 0


Regards

-- 
Camille

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