key the ring
feed front(src clip)& matte into a pixelspread node
play a bit with the params (probably expand > interpolate or stretch)
see the ring disappear ;-))
theres a tutorial
http://area.autodesk.com/blogs/discreetuk/flame_fx_pixel_spread - not exactly the same task, but still you get the procedures
robert
robert coulin
http://www.dreamwalks.com