1. A tangible record carrier storing at least video-related user data and control data in digital form, which control data enable playback control of the user data, which control data comprises at least play control data which defines user data items which are playable, at least selection control data for enabling the user to select and control reproduction of user data and at least variable control data for operating on user and system variables, characterized in that the variable control data comprises at least one instruction for a conditional arithmetical operation.