Place an animated mask on top of another animated mask

Hello !

First, i'm sorry for my english, i hope you will understand what I try to explain.

I want to make a rain of leaf, on a black background. This leafs will show a landscape into theme, here what I want and the landscape I want to show :

I used the mask on a solid layer, but I can't put a layer on an other one because it hide it.

I know I can move the mask with "tracé du masque" :

but I can't have a nice trajectory so I used "position".

So I would like to know if you have a solution for me ? To summarize, I want a leaf rain on a blackbackground wich show an image, like a window.

Thank you very much ! and don't hesitate to tell me if i'm not clear, i will try to explain on an other way