[streaming] MTU option

[Rémi Denis-Courmont]

Le mercredi 29 août 2007, Xiaolin Cheng a écrit :
> hello all,
>
> I set MTU as follows when I streamed out a mpeg4 file:
>
> vlc inputfile.m4v --sout '#rtp{dst=10.0.0.6, port=5000, mux=ts,
> ttl=1}' --mtu 1000
>
> Why is the size of UDP packet captured by tcpdump (764 bytes)
> different from this mtu 1000?

There are two reasons why this is not consistent:
1/ --mtu sets the application-layer MTU. You must add the network and 
transport headers size to get the "real" MTU (such as 28 bytes for 
UDP/IPv4 or 48 for UDP/IPv6).
2/ VLC does not fragment "packets" from the packetizers when sending, so 
if the packetizer emits big frames/packets, you might end up well below 
the requested mtu.

-- 
Rémi Denis-Courmont
http://www.remlab.net/
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