We present Videostrates, a concept and a toolkit for creating real-time collaborative video editing tools. Videostrates supports both live and recorded video composition with a declarative HTML-based notation, combining both simple and sophisticated editing tools that can be used collaboratively. Videostrates is programmable and unleashes the power of the modern web platform for video manipulation. We demonstrate its potential through three use scenarios: collaborative video editing with multiple tools and devices; orchestration of multiple live streams that are recorded and broadcast to a popular streaming platform; and programmatic creation of video using WebGL and shaders for blue screen effects. These scenarios only scratch the surface of Videostrates’ potential, which opens up a design space for novel collaborative video editors with fully programmable interfaces.