This processing sketch will provide a scale up down transition for rectangle and circle

transitions_scale.pde

/**
 * Scale 
 * by Denis Grutze. 
 * 
 * modified by Noel.
 *
 * Paramenters for the scale() function are values specified 
 * as decimal percentages. For example, the method call scale(2.0) 
 * will increase the dimension of the shape by 200 percent. 
 * Objects always scale from the origin. 
 */
 
float a = 0.0;
float s = 0.0;
float m = 0.0;

void setup() {
  size(1280, 720);
  noStroke();
  rectMode(CENTER);
  frameRate(30);
}

void draw() {
  
  background(255);
  
  a = a + 0.04;
  s = cos(a)*2;
  m = map(s, 0, 100, 0, width);
  
  translate(width/2, height/2);
  scale(m); 
  fill(0);
  //ellipse(0,0,150,150);
  rect(0, 0, 150, 150); 
  
  //saveFrame("img-######.png"); 
}