16 inputs is pretty heavy, with ps3eye cams you would need a stack of USB PCIe cards in a super powerful computer (depending on the machine you can get 1-3 per controller and this is not even normal SD video resolution). Just to unpack this many frames is a serious task, let alone doing anything with them. I have worked with multiple ps3eye cams and after 3 everything got flaky (I used 2 separate USB controllers). After that you will also have problems extending them (you have to use active extensions and the PS3eye is picky about this) and a very big power supply, they draw a lot of current I was using full speed USB hubs - full speed is hard to find in a USB hub- and 3 amp power supplies on the hubs, this lessened the power drain on the computer.
If this is a serious project and you have the time and money to make it work there are some other ways to achieve it. There is a 4 input blackmagic capture card (HDSDI --http://www.blackmagic-design.com/products/decklinkquad/), and you can use 4 HDSDI quad splitters --http://www.decimator.com/Products/MD_Quad/MD_Quad.html . You can capture full HD (if your machine has the guts) and break up each signal into 4\. I had to spec this out for a project that never got off the ground and it seemed like one of the simpler solutions, and the only method (4 inputs with 4 quad splits) that is really Isadora friendly and does not need other coding.
From here you can get almost Sd resolution from each camera. It is still resource heavy but this method will work- 16 usb cameras is going to be a hell of a fight.
Again, if it is serious then you can look into using industrial cameras like the fire mv. I have played a little with the SDK and a talented coder could write an input plugin for Isadora without too much hassle. You also get the option of dropping to monochrome on camera to reduce bandwidth use dramatically. There are a variety of machine vision cameras that are designed to be used in large numbers, they have on board memory and you can capture frames synchronously and download them asynchronously, allowing many more cameras on a single system. Again they dont come cheap but the images are great.
You can use the quad split method with cheaper hardware (there is a 4 input analogue card some people use, you will find it in the forum and you can use 4 quad splitters to get 16 low res analogue cameras into your machine.
If you dont need to see all of the cameras at once, try a matrix into the video inputs, you can find many with serial control so you can automate the camera swap. If you are not using cameras with reference in you will get a clunky change as each input re-synchronises.
How many cameras exactly do you want? Do you need them all active at the same time?
