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Hello,
I just wanted to clarify what’s going on here a bit.
First - a little background on Art-Net. Art-Net sends DMX data to Art-Net nodes. It can do this in one of a few ways:
1) The preferred method is to use Art-Net’s built-in discovery protocol. With this, the controller (QLab in this case) broadcasts a poll to the network asking for Art-Net nodes. The Art-Net nodes reply with information about themselves, such as which universes they care about. The controller (QLab) can then send them the DMX data they need directly (not broadcast).
2) The simpler thing to do is simply broadcast all DMX packets to the entire network. The controller doesn’t need to learn about what nodes are on the network, because it sends all DMX data to everything on the network. This is what QLab does if you check the broadcast checkbox in QLab’s preferences (though QLab will still poll for informational purposes, so you can see your Art-Net nodes in the Workspace Status window).
3) Some applications have a manual unicast mode in which the user can enter an IP address to send directly to. QLab currently does not support this mode.
Art-Net is not really designed to have multiple services speaking it on the same machine at the same time. It’s a UDP service, and to receive Art-Net traffic an application must bind to a specific port (6454). QLab binds to this port to receive Art-Net poll replies, which tell QLab about nodes on the network. OLA binds to this port to receive Art-Net DMX traffic. And OS X usually won’t let two applications bind to the same port.
So, when you try to use QLab in the preferred discovery mode with OLA, it does not work because only one of them is able to bind to port 6454. If you launch OLA first, it will bind. QLab will log an error to the system log that it was unable to bind. QLab will send out poll packets, but it could never receive the response because it failed to bind the port to start listening.
If you use QLab in broadcast mode, things can work assuming you start OLA first. If you start QLab first, it will bind the port and OLA will fail to bind. But if you start OLA first, it will be able to receive DMX traffic and QLab will broadcast it. QLab will still log a message about failing to bind the Art-Net port, but that will not prevent it from broadcasting.
I hope that helps.
Thanks,
Chad Sellers
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