I think vMix advises to use USB capture devices for only one, maybe two cameras max (saw that in one of Tim's videos). If you use two, make sure to use separate, distant USB ports, eg. one port on the front, one port on the back of your PC.

Thank you for your prompt reply.

I am also considering:
Connecting several cameras to the Video Grabber 60fps 4K HDMI USB 3.0 1080P and further via USB 3.0 port to the computer. Will there still be a similar problem as above?

What do you think about it.

Thank you in advance for your answer.

This question just never goes away. I did a test using four webcams in 2019. https://www.mgraves.org/...ms-on-a-single-computer/

The result holds true even today and also for USB capture dongles. It's worth noting that some USB 3 capture dongle often don't support MJPEG encoding. Thus older USB2 capture dongles may have an advantage in some cases. Using MJPEG makes it much easier to manage the load and support multiple 1080p input streams.

I suspect there's no "updates" because vMix itself has never had an issue with using multiple USB inputs. They're all just capture devices as far as vMix is concerned. The two real problems, over which vMix has no control, are:-

1) USB Bandwidth. Your PC may only have one USB host chip, even if it has multiple sockets, which will set the limit on the total number of USB capture devices/cameras that can be simultaneously connected. That bandwidth is also affected by the frame rate, resolution and format (compressed or uncompressed) of each USB source. As such, there's no simple answer to "how many?" can be connected, so unless you're able to do the necessary calculations, it's best just to test by adding one at a time (and it's always important to test anyway!). On some laptops with a combination of USB type A ports and USB3.2 type C ports there are two different host chips which should help to increase the available bandwidth, and on a decent desktop PC you can probably add a PCIe USB host card to give you more ports that don't share bandwidth with those built-in on the motherboard.

2) Device driver support for multiple units (of the same type). This is something specific to the brand/model of USB capture device or camera. In some cases, connecting multiple instances of a single device type does not result in each one having a unique entry in the devices listed by Windows, and therefore available to vMix, so vMix typically can only access the first one to be connected. Well designed devices might appear something like "USB CaptureBox", "USB CaptureBox (1)", "USB CaptureBox (2)", etc.