public  function encodeStr(str:String, charSet:String):String

            {

                var result:String ="";

                var bytes:ByteArray = new ByteArray();

                bytes.writeMultiByte(str, charSet);

                for (var i:uint; i<bytes.length; i++) {

                    result += escape(String.fromCharCode(bytes[i]));

                }

                return result;

            }

URLDecoder.decode(trueFileName,"utf-8");