class ProcessFrame extends Thread {
  int[] img;
  ProcessFrame(int[] img) {
    this.img = img;
  }
  public void run() {
    // update sum 
    for(int i = 0; i < len; i++){
      // saves 15 ms from using red() etc.
      sum[i][0] += ((img[i] >> 16) & 0xff) - ((prev[pos][i] >> 16) & 0xff); // red
      sum[i][1] += ((img[i] >> 8) & 0xff) - ((prev[pos][i] >> 8) & 0xff); // green
      sum[i][2] += (img[i] & 0xff) - (prev[pos][i] & 0xff); // blue
      prev[pos][i] = img[i];
    }
    pos = (pos + 1) % avgLength;

    // update recording
    if(frameCount % speedUp == 0) {
      int[] out = new int[len];
      for(int i = 0; i < len; i++) {
        out[i] = 0xff000000 |
          ((sum[i][0] >> avgBits) << 16) |
          ((sum[i][1] >> avgBits) << 8) |
          (sum[i][2] >> avgBits);
      }
      movie.addFrame(out, width, height);
      
      //println(frameRate);
      
      loadPixels();
      arraycopy(out, pixels);
      updatePixels();
      
    }
  }
}