This paper describes a new approach to visualization of scenarios within the use case-based engineering of functional requirements-the so-called video camera metaphor. The video camera metaphor facilitates involvement of business people, customers, problem domain experts and other non-technical stakeholders into capturing and validating formal requirements models. The key tool, supporting the video camera metaphor is the so-called interface editor which allows to draft the prototype user interface and automatically generates a user-friendly front-end to the set of formal modelling tools. The essence of the video camera interface is to associate sequences of events on a UML sequence diagram or an ITU-T message sequence chart with sequences of activations of the elements of the generated user interface. The video camera interface allows capturing scenarios through direct activation of both the input and the output elements of the generated user interface. The generated user interface is also used to replay scenarios for validation purposes.