This is an amazing example of video mapping, celebrating the 600 year anniversary of the Astronomical Clock in Prague.
Video mapping is when the surface you want to project on, say a clock, for instance, is mapped into a computer. The user then sets various points in the computer that correspond to points on the projection’s surface, such as a clock face or some other architectural detail. Then, video can be projected onto the surfaces without any light bleeding into other mapped areas.
To fairly awesome effect, I would say.