They would simply have additional file servers, could be any amount depending on how many video/images. They would possibly have to be in separate datacenters

They would simply have additional file servers, could be any amount depending on how many video/images. They would possibly have to be in separate datacenters though, since shipping large amounts of data over seas can be inefficient and possibly expensive. I'm not sure at what point that starts to be a necessity, they're big but it's still a niche market. And their content is very sparsely visited (i.e. it wouldn't happen often that 80% of their audience would view a single question).