let previousPixels;

​

function setup() {

  createCanvas(640, 360);

  capture = createCapture(VIDEO);

  capture.size(640, 360);

  capture.hide();

  pixelDensity(1);

  noStroke();

}

​

function copyImage(src, dst) {

  let n = src.length;

  if (!dst || dst.length != n) dst = new src.constructor(n);

  while (n--) dst[n] = src[n];

  return dst;

}

​

function draw() {

  capture.loadPixels();

  let total = 0;

  if (capture.pixels.length > 0) {

    // don't forget this!

    if (!previousPixels) {

      previousPixels = copyImage(capture.pixels, previousPixels);

    } else 

    {

      let thresholdAmount = 50;

      thresholdAmount *= 3; // 3 for r, g, b

      for (let y = 0; y < capture.height; y++) {

        for (let x = 0; x < capture.width; x++) {

          let index = 4 * (x + y * width);

          // calculate the differences

          let rdiff = Math.abs(

            capture.pixels[index + 0] - previousPixels[index + 0]

          );

          let gdiff = Math.abs(

            capture.pixels[index + 1] - previousPixels[index + 1]

          );

          let bdiff = Math.abs(

            capture.pixels[index + 2] - previousPixels[index + 2]

          );

          // copy the current pixels to previousPixels

          previousPixels[index + 0] = capture.pixels[index + 0];

          previousPixels[index + 1] = capture.pixels[index + 1];

          previousPixels[index + 2] = capture.pixels[index + 2];

          let diffs = rdiff + gdiff + bdiff;

          let output = 0;

          if (diffs > thresholdAmount) {

            output = 255;

            total += diffs;

          }

          capture.pixels[index] = output;

          capture.pixels[index + 1] = output;

          capture.pixels[index + 2] = output;

          // also try this:

          // capture.pixels[i++] = rdiff;

          // capture.pixels[i++] = gdiff;

          // capture.pixels[i++] = bdiff;

        }

      }

    }

  }

  // need this because sometimes the frames are repeated

  if (total > 0) {

    capture.updatePixels();

    image(capture, 0, 0, 640, 480);

  }

  let avgMotion=total/capture.pixels.length;

  fill(255);

  rect(0,height-avgMotion*20,100,height);

}

​