How do you speed up a part of a video without changing the av sync?

Question

I tried to speed up part of my video (for the chipmunk voice of course) but then throughout the rest of my video that was in real time, the av sync was completely not synchronized. Additionally, imovie did not show evidence of this problem, when I posted it to youtube the av sync was completely off! PLEASE HELP, IT WOULD BE GREATLY APPRECIATED

Answer 1

here's real code:
//where flv is a video displayobject (eg, an flvplayback component)
var bmpd1:BitmapData = new BitmapData(flv.width,flv.height,false);
var bmpd2:BitmapData = new BitmapData(flv.width,flv.height,false);
var bmp1:Bitmap = new Bitmap(bmpd1);
var bmp2:Bitmap = new Bitmap(bmpd2);
addChild(bmp1);
bmp1.x=0;
bmp1.y=flv.height;
addChild(bmp2);
bmp2.x=stage.stageWidth/2;
bmp2.y = flv.height;
this.addEventListener(Event.ENTER_FRAME,f);
function f(e:Event):void{
    bmpd1.draw(flv,new Matrix(),null,null,new Rectangle(0,0,flv.width/2,flv.height),true);
    bmpd2.draw(flv,new Matrix(),null,null,new Rectangle(flv.width/2,0,flv.width/2,flv.height),true);