gistfile1.js

$.fn.sprite = function(options){
  var $el = $(this)
    , frames = options.frames
    , inverse = options.inverse
    , currentFrame = 1
    , size = options.size
    , fps = options.duration / frames
    , positions = ($(this).css('background-position').split(' ') || ' ')
    , top = positions[1]
    , left = positions[0]
    , backgroundPosition;
  
  
  function animate(){
    
    if(inverse){
      top = parseInt(top) - size;
    } else{
      top = parseInt(top) + size;
    }
    
    $el.css('background-position', left+' '+top+'px');
    
    currentFrame++;
    
    if(currentFrame < frames){
      setTimeout(animate, fps);
    }
    
  }
  
  setTimeout(animate , fps);
  
};