Source: Animated/fading texture as an screenoverlay?

I have been looking around the internets for a good solution to fade in a partly translucent texture that is visible through the env_screenoverlay.

This is supposed to be triggered quite often, and I am not really sure on how to go ahead.

I guess it's possible to make it an animated texture for fade in/fade out, and then time that in the actual screenoverlay, but the best solution would ofcourse to have a masked texture with parameters that sets the alpha on the mask through the material.

How would you guys go ahead doing this?

Full screen --> 2 second fade in black letterbox bars --> keep letterbox for 5 seconds --> 2 secound fade out

Yes I looked briefly on that actually, but didn't go far with it. It looks like something that could be useful for this actually.