How to create a 100% width & height picture in edge?

I really love edge animate but something is really freking me out...

How can I get a picture, for example in a symbol, behaving like this:

http://www.dnzstudio.com/clients/fullscreen/muse/index.html

???

I read the forums, looked at youtube tutorials but didm´t find something simple. But their mud be a solution.

I already managed to set on picture like that in the background. also I know the fullscreen function from edge hero (by the way does´t work in firefox at all).

But this are not the solutions I am looking for. I simply want to fill a symbol with a 100% width & 100% height picture which stays in the aspect ratio of the picture.

It should be in a symbol that I can animate it as I want and also create a transition between 2 fullscreen pictures.

Any ideas someone??? Thanks for help!