Burst phase correction system for video descrambling
AssigneeMacrovision Corporation
InventorK. Heinz Griesshaber
Life of this patent
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Abstract
A method and apparatus for synchronizing a randomized video signal to a phase-locked sampling system. The phase-locked system is part of a scrambling apparatus capable of scrambling and subsequent descrambling of video signals recorded on videotape recorders which undesirably introduce time-base errors into the luminance/chrominance phase relationship. These time-base errors are removed without use of a time-base corrector by programmable delay line memory circuitry which introduces a programmable amount of delay into the video path. The delay line includes a programmable length FIFO memory module.
Claims15
A method for capturing a color composite video signal having time base error into a memory for signal manipulation, comprising the steps of:
- storing the composite video signal having the time base error in the memory;
- determining if the color burst of a horizontal line of the composite video signal has a phase discrepancy relative to a reference oscillator phase-locked to color bursts of the prior horizontal lines of the signal after reading the content of the memory;
- providing a delay having an adjustable length;
- adjusting the length of the delay to compensate for the phase discrepancy;
- and
- transmitting the composite video signal through the adjusted length delay.
A method of scrambling and descrambling a color composite video signal comprising the steps of:
- recording the video signal;
- scrambling the video signal by line rotation of each horizontal line thereof;
- determining if the chrominance portion of the composite signal, for each particular horizontal line thereof, has a phase discrepancy relative to a reference oscillator phase-locked to color bursts of the prior horizontal lines;
- digitizing the composite video signal;
- providing a digital delay line having a programmable length;
- programming the length of the delay line to compensate for the determined phase discrepancy;
- transmitting the digitized composite video signal through the programmed delay line;
- replacing the original horizontal synchronization signal in the particular horizontal line with a time-referenced horizontal synchronization signal;
- and
- descrambling the video signal.
A device for capturing a color composite video signal having time base errors for signal manipulation comprising:
- a memory for storing the composite video signal having the time base error;
- means for determining if the color burst of a line of the video signal has a phase discrepancy relative to a reference oscillator phase-locked to color bursts of the prior lines of the signal after reading the video signal stored in the memory;
- a delay having an adjustable length;
- means for adjusting the length of the delay to compensate for the phase discrepancy;
- and
- means for transmitting the composite video signal from the memory through the adjusted length delay.
A device for scrambling and descrambling a color composite video signal comprising:
- a scrambler for scrambling the composite video signal by line rotation of each horizontal line thereof;
- means for determining the amount of phase discrepancy between the chrominance portion of each horizontal line of the scrambled video signal and a reference oscillator phase-locked to a color burst of a prior line;
- a digitizer for digitizing the scrambled composite video signal;
- a programmable length FIFO memory delay line connected to receive the digitized composite video signal;
- means for programming the length of the delay line to compensate for the amount of phase discrepancy in each horizontal line;
- means for time correcting by resetting the horizontal synchronization signal in each horizontal line;
- and
- a descrambler for descrambling the video signal.
Dependencies are inferred from the claim text.