The frame in the frame is a very steep compositional technique. Watch the video about how Paul Thomas Anderson does it.
"In this video essay, I look at a visual device the writer/director employs in all of his films: the frame within a frame. This way of seeing is sometimes a literal movie within a movie, such as the porn in Boogie Nights, or the film screened in the psychiatric hospital from Inherent Vice. But more often, Anderson uses doorframes, hallways, windows and other naturally occurring frames on location to act as a container to his characters. While not always conspicuous, after I removed the audio from the clips and isolated the shots, the visual frames stand out. This ode to Paul Thomas Anderson’s visual predilection captures a trend in his filmmaking that has not been explored in other video essays."