Help with AS to freeze bitmapdata animation

Question

I am using BitmapData to create an animated flag waving with
Actionscript. This is for an ad, so the coded animation needs to
stop after 30 seconds. I would like to "capture" an image from the
animation and use this for the last frame instead of just removing
the dynamic clip from the stage. Does this make sense?

Answer 1

I have:
this.onEnterFrame = animateSlices;
and:
this.animateSlices = function(){
var amplitude = 100; // amplitude (0-100)
var frequency = 85; // frequency (0-100)
//var waves = sliderW/10; // number of waves (0-100)
var waves = 7.9;
//trace(waves);
var tyw = .18;
var byw = sliderBy/100;
var txw = 0;
var bxw = 0;
var w = Math.PI*frequency;
var k = waves/w;
//etc....
The flash movie is one frame.