3 of them? Are they identical USB devices?
Multiple identical USB things can be a problem. It's not an OBS thing at all, but a violation of the USB spec itself, because the devices are *completely* identical, including their serial numbers!
USB requires each device to have a unique serial number, and leaves it up to the manufacturer to decide how to do that. But if that's the *only* difference, then it has a huge effect on cost to make that identical too.
If you only have one of each device, nobody notices. But if you have multiple of the same thing, then it causes problems because the OS can't tell them apart. OBS is not involved here.
Different OS's handle this situation differently. Don't know what Mac does, but:
- Windows seems to use one of them successfully and ignore the others. Don't know if it picks the first one and ignores the rest, or if the next one boots the previous one off, but nevertheless, you end up with just one, and which one that is can be random because things start in random order.
- Linux can use the device tree (which port of which hub it's plugged into) to keep them straight, and thus use all of them. OBS can then use all of them too. But again, the order could be random, which means you'll have to rearrange your assignments in OBS...
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Another possibility is that you're getting choked on the total data rate, and Mac would rather have 1 good one than 3 bad ones. A USB 3 controller is only good for one uncompressed HD video source, because that's already over half of the total that must be shared across everything. Add a second HD video source, and something must degrade in order to get something from both.
If you happen to have two USB *controllers*, then you can have one source on each and have that work.
But if you only have one controller and an internal hub, as is common, then you have a practical total limit of 1 HD source.
