gistfile1.js

$.fn.sprite = function(options){

  var defaults = {
    frames: 10,
    inverse: false,
    size: 20,
    duration: 400
  };

  options = $.extend({}, defaults, options);

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

$.fn.sprite = function(options){

var defaults = {
frames: 10,
inverse: false,
size: 20,
duration: 400
}
, options = $.extend({}, defaults, options)
, $el = $(this)
, currentFrame = 1
, fps = options.duration / frames
, positions = ($(this).css('background-position').split(' ') || ' ')
, top = positions[1]
, left = positions[0]
, backgroundPosition;

function animate(){

if(options.inverse){
  top = parseInt(top) - options.size;
} else{
  top = parseInt(top) + options.size;
}

$el.css('background-position', left+' '+top+'px');

currentFrame++;

if(currentFrame < options.frames){
  setTimeout(animate, fps);
}

}

setTimeout(animate , fps);

};