Another useful concept for these kinds of projects is “state machine”
https://discourse.processing.org/search?q=state%20machine
So you have states like this:
int s0video = 0;
int s0choice = 1;
int s1video = 2;
int s1choice = 3;
int s2video = 4;
int s2choice = 5;
int s3video = 6;
//....
int current = s0video;
and then you have rules like “if the state is s2choice and the mouse clicks on the right hand side of the screen, the state is now s5video”:
if(current==s2choice && mousePressed && mouseX>width/2) {
current==s5video;
}
Draw to the screen displaying the video or buttons based on whatever the current state is.
For previous discussion of sketch state in a simple interactive experience, also see: