Video Timer (HELP)

Through this code my video timer is playing like 00:10 / 11:14

but i want to play in negative of total time like 11:14 then timer should run in negative like 11:13 , 11:12 , 09:00 , 1:00 , 00:10


my code is

function formatTime(t:int):String {
// returns the minutes and seconds with leading zeros
// for example: 70 returns 1:10
var s:int = Math.round(t);
var m:int = 0;
if (s > 0) {
while (s > 59) {
m++;
s -= 60;
}
return String((s < 10 ? "" : "") + m + ":" + (m < 10 ? "0" : "") + m);
} else {
return "0:00";
}
}