1. A tangible record carrier storing at least video-related user data and control data in digital form, wherein the control data enable playback control of the user data, and wherein the 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 variable control data for operating on user and system variables, wherein the variable control data comprises an instruction for performing an operation, the instruction comprising a first byte being an opcode and further bytes of operands, the opcode including a first set of bits indicating type of the operation, a second set of bits indicating a condition code for performing the operation conditionally or unconditionally depending on a value of the condition code, and a third set of bits indicating a type of an arithmetical or logical calculation, wherein the operation is executed if the condition code has a first value and a first condition is met, and wherein the operation is executed if the condition code has a second value so that the operation is performed by execution of a remaining portion of the instruction without jumps and with reduced number of commands.