if you include an image on a website and you don't specify width and height, it won't render until it fetches the image. I understand this.

but I'm wondering how it works with ads, say tribalfusion/etc.

if in the middle of a page I have the ad code, does it need to analyze the ad code, fetch the ad, etc, before rendering?

if it does, can this be fixed by simply putting the ad code within a div that specifies its height/width?

if that trick does work, then how do you deal with ads that may serve in different sizes-- for example, tribalfusion has code to load a 728x90 leaderboard. if there's no inventory for that individual ad, it could serve a 460x60 banner ad instead.

I need ads on this particular site, but I'd like to still keep page load time to a minumum