import processing.video.*;
  
  Capture video;
  int count;
  int writeRow;
  int maxRows;
  int topRow;
  int buffer[];
  
  void setup() {
    size(600, 400);
  
    // Uses the default video input, see the reference if this causes an error
    video = new Capture(this, 30, 20);
  
    maxRows = height * 2;
    buffer = new int[width * maxRows];
    writeRow = height - 1;
    topRow = 0;
    
    //frameRate(10);
    background(0);
    loadPixels();
  }
  
  void draw() {
    for (int y = 0; y < height; y++) {
      int row = (topRow + y) % maxRows;
      arraycopy(buffer, row * width, g.pixels, y*width, width);
    }
    updatePixels();
  }
  
  void captureEvent(Capture c) {
    c.read();
    c.loadPixels();
    arraycopy(c.pixels, 0, buffer, writeRow * width, width);
    writeRow++;
    if (writeRow == maxRows) {
      writeRow = 0;
    }
    topRow++;
  }