Video compositing, the editing and integrating of many video sequences into a single presentation, is an integral part of advanced multimedia services. Single-user compositing systems have been suggested in the past, but when they are extended to accommodate many users, the amount of memory required quickly grows out of hand. We propose two new architectures for digital video compositing in a multiuser environment that are memory-efficient and can operate in real time. Both architectures decouple the task of memory management from compositing processing. We show that under hard throughput and bandwidth constraints, a memory less solution for transferring data from many video sources to many users does not exist. We overcome this using (i) a dynamic memory buffering architecture and (ii) a constant memory bandwidth solution that transforms the sources-to-users transfer schedule into two schedules, then pipelines the computation. The architectures support opaque overlapping of images, arbitrarily shaped images, and images whose shapes dynamically change from frame to frame.