This paper describes Popcorn Movie, a movie-making party game demonstrating a theoretical and practical framework for generating stories using a dynamic narrative feedback loop between the improvised dialogue performed by co-located human participants and textual summaries iteratively generated by a large language model. In Popcorn Movie, human players take turns reading iterative generative summaries and then recording and uploading video clips of themselves performing responding improvised dialogue, which are iteratively edited into a video sequence available for instant playback. The feedback loop between the iteratively generated summaries and responding dialogue improvised by participants produces a spontaneous narrative video with continuity. We will detail the design of Popcorn Movie and the results of the playtests.