Multi camera feature not working

[hombre2021]

I have 2 usb video cameras and one Logitech stream camera. Windows 11 and OBS recognize them all, but after adding them into source and scene, only one camera works inside OBS. On the other ones I get a black screen even after I have selected them from list of existing devices. I can see them in Device manager.
I keep thinking that is because I run them through windows camera management to make sure they can be seen within OBS. Is there a way around windows camera management? Can someone help please?

 

[AaronD]

Usually, the problem with this is USB itself. Uncompressed HD video takes more than half of the available bandwidth, so one is okay but two is not guaranteed. How the second one fails, depends on the details of how your system works. It could refuse to use one or both, or it could degrade one or both to make them fit.

This applies per USB *controller*, not per port, and most systems only have one or *maybe* two controllers, with internal hubs to connect all the ports. On those systems, you're limited to one or *maybe* two USB video sources total, if you can connect them to the correct ports so that each one is on a different controller.

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If you have a spare PCIe slot, then you could put a USB card in it, which would give you another controller.

Or, you could put a multi-input capture card in that slot instead. Make sure all of its inputs work simultaneously: the cheap ones that are designed for security systems, tend to have only one converter (the expensive part) and a quick-and-dirty switch to connect it to one input at a time. You want one that has a dedicated converter for each input.

 

[hombre2021]

OK, I appreciate your answer. My PC is one of those all in One Dell. Is it possible to connect an external card or controller through one of the USB ports? or maybe I am out of luck with this system of mine?

 

[hombre2021]

Maybe using an USB/HDMI capture card would help?

 

[hombre2021]

I think you gave me the answer I was looking for. I ordered 2 capture cards from Walmart so I can start using at least 2-3 cameras. They'll be here tomorrow. I will let you know how it goes, I believe this is my answer. Thank you so much in advance

 

[AaronD]

Is it possible to connect an external card or controller through one of the USB ports?

No.
You're still limited by the internal controller, so there's no point in even making such a thing.

Maybe using an USB/HDMI capture card would help?

Also no.
There *is* a purpose for these, but you're still limited by the internal controller.

If you're using the existing USB, then you still have the same total limit, no matter how you do it.

I ordered 2 capture cards from Walmart...

Are they less than $60 each? If so, then they're probably cheap Chinese garbage with deceptive marketing.

Usually what happens, is they put a cheap USB 2 chip behind a genuine USB 3 *connector* - the additional pins for USB 3 are present but not connected - and then they make a big deal about how much better USB 3 is than USB 2...when those pins aren't even connected and the chip behind it is in fact USB 2 only!

You can't cram even *one* uncompressed HD video source through USB 2, and so that cheap chip has to compress it, hard! And, being cheap, it uses a cheap, easy, and inefficient method to do it: MJPEG, which is simply a JPG still image of each frame with no knowledge of the other frames so as to take advantage of their similarity. So the quality is even worse than the limited bandwidth might dictate otherwise.

And, you can't put multiple USB 2 devices on a USB 3 hub and expect them to share the USB 3 bandwidth back to the controller. That's a massive mistake in my opinion, on the part of the USB designers, but it's done that way on purpose for who-knows-why. USB 2 and USB 3 remain completely separate through all the hubs and all the way back to the controller, so that the USB 3 wires remain unused as you load up more and more "high bandwidth" USB 2 devices so that the USB 2 side chokes.

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There's no getting around this. If it all goes through the original USB controller(s), then you're limited to that many video sources, no matter how you do it. And cheap video -> USB captures have even more problems.

If you must use USB video captures, stick with the name brands - not Walmart or Amazon or any other distributor, but the actual brand itself - that actually care about customer loyalty and thus have some accountability to those customers. Expect to pay about $80 to $120 per input. And the same limit still applies: only one of them per *internal* USB controller.

My PC is one of those all in One Dell...maybe I am out of luck with this system of mine?

I think so. Get something else that has at least 3 PCIe slots:

• 2 for a good graphics card / GPU (nVidia seems to be the most popular, and therefore best supported, for video production)
• 1 for a four-input HDMI capture card, all of which work simultaneously (not a cheap security thing that only does one at a time)
• more for whatever else you might want to add

Multi-input capture cards on PCIe are often cheaper per input than USB, *and* all of those inputs can work simultaneously. Win-win. But still be careful, and don't fall for a cheap scam.

 

[AaronD]

...cheap, easy, and inefficient method to do it: MJPEG...So the quality is even worse than the limited bandwidth might dictate otherwise...
...
And, you can't put multiple USB 2 devices on a USB 3 hub and expect them to share the USB 3 bandwidth back to the controller...

I will let you know how it goes...

It's possible that you don't notice the degradation. I had 4 identical cheap HDMI -> USB capture cards before I got fed up with a different problem and replaced them with a four-input PCIe card.

I was just starting out, and didn't realize how bad the picture was until I saw how much better the PCIe card is. With 4 of them all sharing a single USB 2 controller (see above about USB 3 hubs, which I *was* using), it really was pretty bad! All of them degraded enough to take no more than 1/4 of what a single USB 2 controller can do. But I was just starting out, and didn't notice with all of the other fires I was trying to put out.

The problem that I got fed up with, was random latency/delay. These 4 cheap supposed-to-be-identical USB captures were always out of sync *with each other*, and by different amounts and directions every time I turned the rig on! Good luck chasing *that* with manual delay settings!

The single PCIe card not only fixed the sync problem, but it also has lower latency / less delay than the USB captures ever had.

 

[AaronD]

And one more problem that cheap identical things tend to have, is that even their serial numbers are the same.

That's a big deal for manufacturing costs, and nobody notices as long as there's only one of them per computer. But if you do have multiple devices on the same computer, that really are *completely* identical including the serial number, that causes problems too.

Windows, I believe, will only use one of them. Whether it ignores the later ones or bumps the earlier ones off, I don't know, but it hardly matters. If they have different serial numbers, then it works...with the caveats mentioned above.

Linux can use the physical tree - where each one is plugged in, including which port on which hub - to keep them separate and use all of them. But their order in the list to choose from is effectively random, so you could end up having to fix which camera is what every time you turn the rig on. I did that when I had the 4 USB captures...no more with the direct video -> PCIe card.