It all depends on what you need.
Computer, ideally Quad i7 Haswell or better CPU but it can make do with less.
Desktop and laptops have different inputs and different sources are handled differently which is why it’s difficult to answer your question.
You can use anything from a webcam and small laptop to a desktop with input cards for 4 or more broadcast SDI cameras. All that’s “required” is a webcam.
Could be a laptop with USB3 port. A Blackmagic or Magewell HDMI input device and an inexpensive consumer camera. You’d want to bring in a mic as well for the performer audio. That could go into the camera or a mixing board into USB3 or a mic straight into USB2..
My personally preferences would be 15″ MBPr with two Blackmagic MiniRecorders and two video cameras of your choice. Audio really depends as there’s lots of variables depending on stage, performers, distance to computer.