keynote: animate slide with opening curtain movie to have curtain open to reveal text

Using Keynote 10.1 I inserted on a slide an mp4 movie of a red stage curtain opening horizontally (from center to left and right simultaneously) onto a black background. I have a second slide with text (white font on black background) that I want to be revealed as the curtain opens, or if that is impossible as soon as possible after the curtain finishes opening. I imagine that a "magic move" is what I need to do (?) and I have studied tutorials on how it works, but I need detailed advice about what to do for my opening curtain problem. Thank you.