"As Brandon described, ...this technique is all about creating a film out of the unexpected, with minimal planning and forethought, and improvising when needed. Brandon often stumbles onto scenes that he wants to film. He emphasizes that in these cases, filmmakers should just start shooting to establish the scene, and then go in closer for the interesting angles and multiple takes. Brandon stresses, “Seek a moving subject and find unusual angles. If you’re uncomfortable, you might be doing it right.” Why? “It means your audience has probably not seen that often.”"
Source: https://vimeo.com/blog/post/explore-improv-filmmaking-with-pro-brandon-li
His commentary on the video and how it was made:
