Apparatus for scrambling a digital video signal

Apparatus operable in an intermittent scrambling mode and a partial scrambling mode for scrambling a digital video signal, comprising:

• means for encoding a digital video signal to supply successive frames of video data as an output, each of said frames of video data having a respective frame number and being comprised of blocks of video data with each block including a respective block number for identifying that block within the frame;
• means for adding frame-scramble-off data to those frames of video data having a frame number equal to one of a plurality of predetermined frame numbers and for adding block-scramble-off data to those blocks of video data having a block number equal to one of a plurality of predetermined block numbers;
• scrambling means operable in both said intermittent scrambling mode and said partial scrambling mode to scramble all of said blocks of video data included in those frames not having said frame-scramble-off data, and operable in said partial scrambling mode only to scramble each block of video data not having said block-scramble-off data in those frames having said frame-scramble-off data;
• and
• for providing as a scrambled video signal a frame comprised selectively scrambled and selectively unscrambled blocks of video data.

Apparatus for descrambling a partially scrambled digital video signal, comprising:

• means for receiving frames of video data, each frame being comprised of respective blocks of video data with each block having either block scramble-off data or block scramble-on data;
• means for descrambling each of said blocks of video data having said scramble-on data to produce respective descrambled blocks of video data;
• and
• means for decoding said descrambled blocks of video data and said blocks of video data having said block scramble-off data to produce a decoded digital video signal.

Apparatus for descrambling an intermittently scrambled or partially scrambled digital video signal, comprising:

• means for receiving frames of video data, each frame having frame scramble-on or frame scramble-off data and respective blocks of video data, with each block having either block scramble-on or block scramble-off data;
• means for descrambling each block having block scramble-on data in those frames having said frame scramble-on data to produce respective descrambled blocks of video data;
• and
• means for decoding said descrambled blocks of video data and each block not descrambled by said descrambling means.