import ddf.minim.*;

Minim minim;

AudioPlayer player1;
AudioPlayer player2;

int size = 1;
int direction=1;

void setup(){
  size(500,300);
  
  minim = new Minim(this);
  
  player1 = minim.loadFile(“file1.mp3");  //replace with your file name
  player2 = minim.loadFile(“file2.mp3");
  
  player1.play();
  
  background(0);
}

void draw(){
 
  background(0);
  
  if(player1.isPlaying()==false && direction==1){
    player2.rewind();
    player2.play();
    direction=-1;
    
  } else if(player2.isPlaying()==false && direction==-1){
    player1.rewind();
    player1.play();
    direction=1;
    size=1;
  } 

  size+=2*direction;
  ellipseMode(CENTER);
  noStroke();
  fill(255,0,0);
  ellipse(width/2,height/2,size,size);
  
}