Spinning Disc's Direction

A spinning disc is painted black on one half and white on the other (i.e., the line forming the border between the black and white regions of the disc is a diameter of the disc).
The disk is spinning on a turntable in an unknown direction at an unknown speed. You have special video cameras that can observe the color of a single point on the disc.
How many cameras do you need to determine the direction the disc is spinning?

Answer is a integer. Just put the number without any decimal places if its an integer. If determining the direction is not possible, output Infinity.

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