There is currently no way to request a specific input, such as the microphone or the line-in, and what you actually get a handle on is not entirely consistent across platforms. 

 

1. import processing.video.*;
   //import processing.opengl.*;
   
   PImage img;
   int diameter=20;
   Capture cam;
   
   
   void setup() {
    frameRate(15);
    size(640, 480, OPENGL);
    colorMode(RGB,255);
    noStroke();
   
    cam = new Capture(this, 80, 60, 20);
    cam.start();
   }
   
   
   void draw() {
   
    if (cam.available() == true) {
      background(125);
      cam.read();
      img = cam;
   
      for (int w=0; w<img.width; w++) {
        for (int h=0; h<img.height; h++) {
          fill(img.pixels[w+h*img.width]);
          ellipse(w*diameter, h*diameter, diameter, diameter);
        }
      }
    }
   }