The saveFrame() function allows you to save images from a program while it is running. This example saves the first 50 frames of a program. These images can be imported into animation software or QuickTime and then saved as a movie.
Original Processing.org Example: SaveManyImages
// All Examples Written by Casey Reas and Ben Fry // unless otherwise stated. float x = 33; float numFrames = 50; void setup() { size(200, 200); smooth(); noStroke(); } void draw() { background(0); x += random(-2, 2); ellipse(x, 100, 80, 80); if (frameCount <= numFrames) { saveFrame("circles-####.tif"); } }