n = 0;
if (marker.numKeys > 0){
  n = marker.nearestKey(time).index;
  if (marker.key(n).time > time){
    n--;
  }
}

if (n == 0){
  value;
} else {
  max_dev=20; // max deviation in pixels
  spd=35; //speed of oscillation
  decay=10; //how fast it slows down
  t = time - marker.key(n).time;
  s = max_dev*Math.sin(spd*(t))/Math.exp(decay*t);
  value + [s,s];
}