Method and apparatus for secure transmission of video signals
AssigneeBritish Broadcasting Corporation
InventorsAdrian P. Robinson, Christopher K. P. Clarke, Andrew J. Bower
Life of this patent
Estimating the term…
Abstract
Video signals are sampled at 4Fsc locked onto sub-carrier phase and frequency. The active picture lines of each field are divided into 6 blocks of 47 lines and the active line periods of those lines scrambled on a block by block basis by line order shuffling. The shuffling algorithm is generated by a line shuffling permutator driven by a PRBS generator (controls 36, 38). Active line period samples for one block are written in unscrambled form into a first memory block (32) and samples from the previous block are read out in scrambled form from a second memory block (34) for transmission. The complementary process takes place in the decoder.
Claims24
A video signal encoder for providing a scrambled video signal output, comprising means for sampling an input video signal, means for digitising the sampled signal, means for subdividing the digitised sampled signal into a plurality of blocks of active picture lines, and means for shuffling the line order within each block according to a predetermined sequence to scramble the signal, characterised in that the colour bursts of shuffled lines remain in position and that the sampling frequency is an integral multiple of four times the frequency of the reference colour subcarrier of the video signal.
A video signal decoder for providing a clear output suitable for display from a received scrambled video signal, comprising receiving means for receiving the scrambled signal, sampling means for sampling the received signal, digitising means for digitising the sampled signal, subdividing means for subdividing the digitised sampled signal into a plurality of blocks of active picture lines, and shuffling means for shuffling the order of lines in each block according to the inverse of the predetermined shuffling sequence used to scramble the signal, characterised in that the received colour bursts of shuffled lines remain in position and in that the sampling frequency is an integral multiple of four times the frequency of the reference colour subcarrier of the video signal.
A video signal transmission system comprising:
- at a transmitter:
- an analog video signal source;
- an encoder for scrambling the analog source comprising means for sampling the source signal at a frequency an integral multiple of four times the frequency of the reference colour sub-carrier of the video signal, means for digitising the sampled signal, means for sub-dividing active picture lines of the signal into a number of blocks of lines, and means for shuffling the order of lines within each block according to a predetermined sequence to produce a scrambled signal, wherein the colour bursts of shuffled lines remain in position;
- and
- means for transmitting the scrambled video signal in analog form;
- and at a receiver;
- means for receiving the scrambled video signal;
- a decoder for providing a clear video signal for display or storage from the scrambled received signal, comprising means for sampling the received signal at a frequency an integral multiple of four times the frequency of the reference colour sub-carrier of the video signal, means for digitising the sampled signal, means for sub-dividing the digitised sampled signal into a number of blocks of lines and for shuffling the order of lines within each block according to a predetermined shuffling sequence the inverse of that applied to shuffle the lines at the transmitter to produce a clear signal, wherein the colour bursts of shuffled lines remain in position;
- and
- means for displaying or storing the clear signal.
Dependencies are inferred from the claim text.