Specifies how the interface shall operate. When the port is
set as an input, then a video stream received on the physical
port is distributed to the objects having this port as their
input. When the port is set as an output, then a video stream
received from the object referenced in vasIfInputFrom is
transmitted on the physical port.
asiInput(1). The port shall operate as an ASI input.
asiOutput(2). The port shall operate as an ASI output.
sdiInput(3). The port shall operate as an SDI input.
sdiOutput(4). The port shall operate as an SDI output.