AFAIK there is no limit on Vmix SD - 1000 capture inputs, like to see a computer that can do 1000. (says limit is the same as Vmix HD).

I've worked with 4 x Magewell USB devices (which emulate a Webcam as they don't use a driver) with VMix HD. In theory what you are doing should work fine.

Maybe see if you can get another program to take the 3 x SD USB cameras and display them on the screen @ once to see if it's VMix or your system/cameras/drivers are just not doing it?

You need to work through a pattern of elimination to gain more information. Trying different things until you have enough information to figure out the true cause of the problem.

I'd try booting with them all plugged in. Adding them after boot, changing the order. Trying to figure out which USB buses the cameras are on, often USB ports share a channel or bus. Sometimes moving the Cameras around will spread the load more evenly across those buses. On HD Cameras this is very important, on SD Cameras it may not be as critical since they would require less bandwidth on the usb. Keep notes of what you have tried already and hopefully you will see a pattern and work out why. Once you understand why your setup works in that manner it's easier to configure it correctly.

Drivers could be very important if your Cameras actually require drivers.

Of course check all Cameras are actually set to a max resolution of 768x576 and you didn't just set something to a default resolution higher than your Vmix license allows, could be as simple as that.

I greet, think you gave me a lot of help.
Everything is OK now.
It was in USB input problem.
All three cameras work properly.
By the way, look for help entering a source through Skype talk...
I send you heartfelt thank
Apostolos

I have been running into the same or similar experience. We are trying / wanting to have three cameras, a green screen and additional capture ports for sound, PowerPoint, video, screen capture, title overlays, slit or multiple screens etc....

I don't know if I am doing something wrong or not but it tells me I am only allowed two capture ports? I am trying the basic. My question is which plan do I need as an adequate plan for what I have mentioned. We are just a small not for profit and can't afford the larger program model so I don't want to keep trying to make it work if that is what I will have to use. Sorry for the lengthy question but I am unclear as to what classifies as to put me over the limit for the above needs with additional room or options to spare..

Also, are there any training videos on green screen or chroma key which have been produced with the most recent release?
How to use an external monitor and other training would also be helpful...

Thank you

The basic HD version $60 allows 3 cameras. That might be sufficient.