What video formats (hopefully WMV) support transparencies?

I'm trying to animate my desktop application for a client.

I would like to animate the background with a loop and o开发者_JAVA百科ffer region specific animations on top of this (allowing transparencies to see the layered animations underneath).

Is this possible with WMV? If not, is it possible with another video format?

Quicktime movies support alpha channel transparency if the codec does. The "Animation" codec is commonly used for that purpose.

I don't think it supports any of that, I think what you have to do is overlay stuff with transparency.