How does video come on the walls of the buildings?

Taking into account that everything magic in the movie was actually not, and that there was an extensive use of gadgetry by The Eye; the obvious answer to this question would be - technology. Or to be more precise - projectors, holographic displays of some sort. Earlier in the movie, when the Horsemen are first summoned, we see a holographic projection created using four projectors planted in the room.

Also, at the last show, we can see them standing in front of a projection generator (the glowing circle like stands). So what all this is supposed to explain, is that it is an incredibly clever use of lights and holographs that make it possible to create such illusions. (please don't go for scientific plausibility on this one)

Actually that's just using 3D/4D projections. Pretty cool technology, been around a few years now. Here is a fun example.