| 摘要 |
Method and apparatus for disabling the effect of video copy-protect signals using differences in the characteristics of television and VCR circuitry. Copy-protect signals include pseudo-sync pulses and/or added AGC pulses in the video blanking interval. The method alters the level of the video signal during the vertical blanking interval, e.g., level-shifting, to render the copy-protect signals ineffective to prevent unauthorized copying by a VCR. The apparatus includes a sync separator (44) for detecting the vertical blanking interval, pulse generating circuits (58, 60, 62, 72, 74) for producing pulses of predetermined widths during this interval, and a summing circuit (88, 90, 92) for summing the predetermined pulses with copy-protect signals thereby to shift their level. An alternative method increases the effective frequency of the copy-protect signals during the vertical blanking interval to achieve attenuation and/or low-pass filtering in the VCR circuitry thereby rendering the signals ineffective in preventing copying. |
