using a flv as a mask...?

[dtrace]

I'm trying to replicate this effect on ...

http://www.tedperez.com/archive/sweeneytodd/

The way the image on the home page is revealed...as if a gradient is bleeding into a piece of paper. It was done using an animated smokey gradient type effect made in after effects, and then exported as a swf.

I actually have the swf file. The issue is, how do I use it to mask out an image.

So basically, i have a swf file with an flv in it, that is using it's alpha...and I want it to mask another image in flash.

how would i do this?

How did they do it?

Thanks,

[dtrace]

If you go into the site... there is a mask effect that is used to reveal the image on the home page. It sort of bleeds outward in a very organic way.

http://www.sweeneytoddmovie.com/

The file they are using is an flv....that looks like this...

http://sashagrey.com/burn.html

But how can you mask another image using an flv with an alpha channel? did they somehow use blending modes? or am I missing something about masking?

Thanks.