function prevvid(img) {
   if ($(img).attr('src').search(/\.jpg/) != -1) {
       	 $(img).attr('src', function(i, val) {return val.replace(/\.jpg/, '.gif');});
   }
}

function prevout(img) {
   if ($(img).attr('src').search(/\.gif/) != -1) {
      $(img).attr('src', function(i, val) {return val.replace(/\.gif/, '.jpg');});
   }
}
$(document).ready(function() {

	$("span img").mouseover(function() {
		prevvid(this);
	});
	$("span img").mouseout(function() {
		prevout(this);
	});

});