I suspect that you will not be able to do this with webcam . If you were using cameras which supported hardware trigger, then you could wire up a trigger and trigger them at the same time, and read in the data. As it is now, you are using software trigger and there is no promise made that software triggers will even attempt to synchronize multiple cameras even when given as a vector to start(). Cameras that support external trigger are not necessarily much more expensive than webcam but they are seldom marketed as "webcam".
Best Answer