The invention relates to an arrangement for deriving an ancillary signal from a compressed digital video signal (e.g. MPEG). The ancillary signal comprises selected parts of the main signal, for example, the DC coefficients of I-pictures, or the unscrambled parts. The ancillary signal thus obtained can be used for display in a (multi-) picture-in-picture television receiver, or as an nullappetizernull in order to encourage the user to pay a subscription fee. The ancillary signal can separately be recorded in digital video recorders so as to assist the user in finding the beginning of a scrambled program on tape. The ancillary signal can also be generated at the transmitter end and transmitted at a low bit rate. A decoder for decoding such an ancillary signal is considerably simpler and less expensive than a full-spec MPEG decoder.