$(document).ready(function(){

    function swapArrow(direction){
        var img = document.getElementById("leftMp3Arrow");
        if(direction==1){
            img.src = "../images/evolution/mp3-arrow-right.png";
        }
        else{
            img.src = "../images/evolution/mp3-arrow-left.png";
        } 
    }
    
    $("#leftMp3").hover(function(){
        $(this).stop(false,false).animate({marginLeft : "0px"},500,"linear",function(){swapArrow(1)});
    },function(){
        $(this).stop(false,false).animate({marginLeft : "145px"},500,"linear",function(){swapArrow(0)});    
    });
});