Mac OS X - Multicast UDP not working?

[Christophe Massiot]

At 14:27 -0400 19/07/2002, Talbert, Scott wrote :

>I don't know why exactly VLC expects UDP packets to be < 1500 
>bytes.  I suggested (to Christophe, on the VLC team) that they be 
>able to handle packets up to 64K in size (the UDP limit) but he has 
>not responded yet.

VLC expects UDP packets to be < 1500, because I don't see the point 
in sending bigger packets on Ethernet networks. It will just increase 
fragmentation for no gain. But anyway since people are actually doing 
it, we'll have to find a solution.

I needed some thinking and I finally decided not to follow your 
advice. The reason I'm skeptical is because as per the VLC structure, 
packets are always allocated with DEFAULT_MTU size. But if the server 
sends 1500-bytes packets, we lose 65536-1500 = 64036 bytes. There can 
be thousands of packets in the decoder buffers, so we would explode 
our current (quite low) memory requirements. A workaround would be to 
memcpy the big network buffer to a buffer allocated with the right 
size, but it has always been against our policy to add unnecessary 
memcpy()s, for obvious performance reasons.

So what I have done is add a --mtu option. By default it is still 
1500 bytes, but you can change this value without recompiling. This 
option should be added to the GUI Preferences windows, so that it can 
be changed permanently.

-- 
Christophe Massiot.

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