Marking a video and/or audio signal

#The invention relates to a method and arrangement for marking a video or audio signal. The invention also relates to a method and arrangement for decoding said marked signal and a recording medium on which said marked signal is recorded.

#Known methods of marking a video signal are disclosed in WO 93/00769 and EP-A 0 518 616. The known methods modify a video signal such that certain disturbances in the picture are introduced upon playback. It is also known to mark a video signal by adding data to the signal. One method is to accommodate data in the vertical blanking interval. Another method is to blank a rectangular picture portion and replace said picture portion by a sequence of white and black spots that can be detected by a photodiode in front of the picture tube.

#Nowadays, the subject of marking a signal is especially relevant with respect to the copy protection of digital video discs. It is desirable to provide the signal with a detectable code ("watermark") so as to identify the signal as being authentic and to render reproduction of the signal possible under specified conditions only. Video disc players are envisaged that are adapted to playback authentic video discs only. They reproduce recorded program material only if the video signal's watermark corresponds with a code ("wobble key") physically embedded in a given groove of the disc and not provided on a recordable disc.

#FIGS. 1 and 2 show embodiments of arrangements for marking a signal in accordance with the invention.

#FIG. 3 shows an arrangement for detecting a marked video and/or audio signal in accordance with the invention.

#FIG. 1 shows one embodiment of an arrangement for marking a video and/or audio signal in accordance with the invention. In this Figure, reference numeral 1 denotes a video signal source which generates a conventional video signal in the form of a luminance component Y and two chrominance components U and V. The luminance component Y is directly applied to a conventional video encoder 2. The chrominance components are applied to said encoder via respective modification stages 3 and 4 which, in the present embodiment, are adders. The video encoder 2 encodes signal component Y and modified chrominance components U' and V' into a composite signal for transmission in accordance with a given standard such as PAL/NTSC/SECAM (analog) or JPEG/MPEG (digital).

#The arrangement further comprises a black luminance detector 5 which produces a control signal Y=0 if the luminance value Y is substantially zero, i.e. if the corresponding picture area is black. The control signal Y=0 is applied to a mark generator 6 which, in response thereto, produces predetermined non-zero signal values u and v are. The values u and v added to the chrominance components U and V by adders 3 and 4, respectively. For natural video source material, the signal components Y, U and V from video signal source 1 are all zero in black picture areas. The arrangement provides that the video encoder 2 encodes Y'=0, U'=u.noteq.0 and V'=v.noteq.0 in said areas. For non-black picture areas, the mark generator 6 is inactive and the video encoder encodes Y'=Y, U'=U and V'=V as in conventional arrangements.

#The arrangement shown in FIG. 1 relies on the presence of black signal portions in the picture. FIG. 2 shows a further embodiment of an arrangement which forces a predetermined signal portion of the picture to be black. FIG. 2 also illustrates that the modification stages 3 and 4 (which are adders in FIG. 1) may be switches. The arrangement shown in FIG. 2 operates as follows. During the predetermined signal portion (for example, the first or last active video line or portion thereof), the mark generator 6 controls a switch 8 to apply a luminance value Y=0 to the video encoder and, simultaneously, controls switches 3 and 4 to provide non-zero chrominance values U=u and V=v. The predetermined signal portion is defined by a timing circuit 7 which receives a conventional synchronization signal S from the video source and produces a timing signal SP which defines the period of time when the mark generator 6 is to be active.