Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N5/00—Details of television systems
  • H04N5/76—Television signal recording
  • H04N5/91—Television signal processing therefor
  • H04N5/913—Television signal processing therefor for scrambling ; for copy protection
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N5/00—Details of television systems
  • H04N5/76—Television signal recording
  • H04N5/91—Television signal processing therefor
  • H04N5/913—Television signal processing therefor for scrambling ; for copy protection
  • H04N2005/91307—Television signal processing therefor for scrambling ; for copy protection by adding a copy protection signal to the video signal
  • H04N2005/91314—Television signal processing therefor for scrambling ; for copy protection by adding a copy protection signal to the video signal the copy protection signal being a pulse signal inserted in blanking intervals of the video signal, e.g. pseudo-AGC pulses, pseudo-sync pulses

Definitions

• This invention relates to a method of preventing unauthorized copying of video tape cassette recordings and an apparatus for executing the method.
• the method is based on a procedure by which, when producing video cassettes intended to be held for sale or lease by copying (dubbing) an original video tape recording, strong signal components are introduced into the video signal to be recorded, which signal components modify the recorded signal in such a manner that, should the video tape thus produced be unduly copied, a satisfactory video picture of such "pirate” video tape would not be reproduceable, while, however, the authorized "original copies” produced by means of the method according to the invention are reproduceable in conventional video tape recorders (VTR:s) without the modifying signal recorded thereon adversely influending the reproduction quality of the video picture.
• VTR video tape recorders
• the modification signal applied to it will have an influence on the recording signal of the copying VTR that such copies of the "original” copy, when played back, will give rise to inacceptable pictures: The picture rolls, loses colors and synchronization.
• the modification signal acts as an interference signal which effectively destructs the entire picture content of the video tape.
• This invention relates to a method of this kind which is particular ⁇ ly suited to be used for producing, by simultaneous copying, a plurality of video tape cassettes intended to be held for sale or let out on hire and each containing a copy of a video signal recording on an original video tape, a 1"- tape for instance, comprising vertical and horizontal synchronizing signal, color signal, and picture signal portions, and in which the recorded signal has been modified in accordance with the invention to make difficult or prevent production of useable copies by copying the cassettes thus produced.
• the method of recording (dubbing) such video tape cassettes is executed in such a manner that the video signal generated by a unit back-playing an original video tape (usually a so called l"-machine) within the signal intervals thereof which for each picture contain the vertical synchronizing signal and/or the signal interval immediately following the vertical synchronizing signal, within which interval the video signal for each picture contains a first number of horizontal synchronizing signals which, during the immediately following line period, do not contain picture information signal, while being transferred as input signal to a video tape recording apparatus for recording video tapes of video cassettes intended to be held for sale, is superimposed by a modification signal, the amplitude of which is several times larger than the amplitude of the vertical and horizontal synchronizing signals and preferably several times larger than the normally maximum amplitude of the picture information signal portions of the video signal.
• a modification signal the amplitude of which is several times larger than the amplitude of the vertical and horizontal synchronizing signals and preferably several times larger than the normally maximum amplitude of the picture information signal portions of
• the automatic gain control which is always present in conventional equipments for recording and back-playing video cassette tapes and which control the recording level in dependence of the amplitude of the synchro ⁇ nizing pulses, when copying a video cassette recorded according to the invention is supplied with an entirely erroneous control signal for the AGC, and, due to the presence of the modification signal, brings down the recording signal to such low level that the picture and synchronization signal content recorded on the copy tape is incapable of producing an acceptable video picture.
• AGC automatic gain control
• the modification signal is applied within the interval of said first number of horizontal synchronizing pulses during a picture frame which is not immediately followed by picture content signal, the influence of the depression of the amplification of the then following horizontal synchronizing pulses and picture signal during the following picture being maximum.
• the main frequency of the modification signal should be adjusted so as to be located within the range of maximal sensibility of the automatic gain control of the recording machines normally necessary for producing acceptable copies of video tapes.
• This maximal sensibility is usually present in the range of 20 to 50 kHz, somewhat varying for different picture systems in dependence of the horizontal synchronization frequency.
• the modification signal is implemented in the form of signal bursts in each picture sequence, the length and/or position of which within said interval is being continuously varied, preferably at random.
• Figure 1 shows a block diagram of an apparatus for simultaneous production of a plurality of copies of an original video tape, said copies being modified according to the invention
• Figure 2 is a graph showing such portions of a video signal generated by a back-playing videomachine and of special interest in connec ⁇ tion with the modification of this video signal which is introduced according to the invention while copying the orignal tape,
• FIG. 3 illustrates an implementation of the method according to the invention
• Figure 4 illustrates a result of a recording obtained on a video tape produced by copying in a conventional video tape recorder a video cassette tape produced according to the invention.
• FIG. 1 block 1 represents an apparatus comprising a video machine 1 for back-playing an original tape, a l"-tape, for instance, and pertaining means for automatic gain control, AGC, in dependence of synchro ⁇ nizing impulses and color beam.
• This apparatus below called master, delivers at its output terminals a duly adjusted video signal which, when producing tapes in or for cassettes intended to be used in conventional VTS:s, is usually applied directly to a booster amplifier 2, to the output terminals of which is connected a plurality of video tape recording machines 3, slaves, in which tape cassettes intended to be held available to the public are produced.
• the signal as delivered by the master, block 1 has the conventional waveform as illustrated by Fig. 2, in which along the time axis t_ the signal intensity I is shown for a vertical synchronizing signal, the time vs, and the first portion of the time hs during which the horizontal synchronizing signals are present.
• This last mentioned region is of interest in connection with this invention, although part of the interval vs may as well be utilized, however not to such an extent as to spoil the vertical synchronization.
• An apparatus for executing the method according to the invention differs from the conventional arrangement in which, as described, a video signal having a progress corresponding to the one illustrated by Fig. 2 is directly transferred from a master unit to one or more slave video cassette recorders (VCR's) via a booster amplifier 2, in that it comprises means for implementing on the video signal delivered by the master a pulse train, the pulses of which occur within the said intervals vs_ and ihs.
• the signal thus obtained is supplied to the booster amplifier 2 so that the signal recorded on each slave cassette tape within said intervals.
• -said means comprise a pulse train generator unit 4 for generating signals in the form of a pulse train required for modifying the video signal and comprising means for setting duration, position in time, and amplitude of the pulses of said pulse train, a detector unit 5 for detecting the time of appearance of the interval (vs + ihs) of the video signal intended for implementation of the modification signal, and a pulse implementation unit 6 for superpositioning the modification signal pulses on the video signal within said interval (vs + ihs) thereof.
• the video signal On its way from the master 1 to the booster amplifier 2, the video signal passes the detector unit 5.
• the detector unit 5 delivers a trigger signal to pulse train generator 4, causing this unit in dependence of choice of pulse position and pulse train duration within the synchronization interval (vs + ihs) for each picture to deliver a pulse burst to pulse implementation unit 6, in which unit said pulse burst is superimposed on the video signal within the time interval determined by means of said pulse duration setting means of the pulse train generating unit 4, e.g., as shown in Fig. 2, a pulse train with the duration p_.
• Fig. 3 illustrates an example of the shape of signal obtained after the pulse implementation and applied to the booster amplifier 2, a shape which can as well be said to be representative for the shape of the recording obtained on the tape of video cassettes produced in the slave machines 3.
• the shape and amplitudes of the recorded signal exactly correspond to the signal shown in Fig. 2 and do, consequently, constitute a recording exactly corresponding to the original one.
• a burst of pulses 11 are superposed on the video signal during the interval between the arrows 8 (in Fig. 2 the interval P3) located within the interval (vs + ihs) mentioned above and in Fig. 3 indicated by arrows 9.
• the amplitude in the recorded signal of the maximum picture signal portions on the tape may be presumed to originate from a signal amplitude in the signal transferred to the booster amplifier 2 from the pulse implementation unit 6 having a maximum signal strength e, the amplitude of the signal then appearing during the implementa ⁇ tion then being a factor k larger than e_.
• the value of k may preferably be between 3 and 6. The optimum value is to some extent depending on the amplitude of the color beam at the beginning of the original tape, "the 1"- tape" if such tape is used, and adjusted correspondingly.
• the magnetic counterpart to the factor k_ as regards the efficiency of the recording on the tape during play-back may, within the range of the response characteristic of the tape material above the range used for the picture signal, be much lesser than the k_ value in the electric signal when recording.
• the graph of Fig. 4 in which the scale of the ordinate axis is considerably smaller than in Fig. 3, illustrates in principle the shape of a signal recorded on a video cassette tape when copying a video tape cassette produced according to the invention by means of a domestic video tape recorder equipped with conventional recording facilities. Due to the strong modification signal implemented on the tape of the "pirate" cassette, the AGC of the VTR, actuated by the modified signal, presses down the amplification of the VTR in such degree that the recording present on the copy cannot be used for playing back an acceptable video picture.
• the large amplitude of the implemented signal 11, Fig. 2 lowers the amplification in the unit to such an extent that the amplitude of the recording e r of this signal . on the copy during play-back will not be larger than in the order of 0,2 to 0,5 of the maximum magnitude e_ of the picture signal 10, the picture signal being lowered in the same relation.
• a video cassette tape having a recorded signal generally corresponding to the ones shown in Figs. 2 and 3 was copied in a video recording machine delivering a highest peak-to-peak-voltage of 1 volt in accordance with known standard.
• the values of the characters pulse amplitude, pulse duration, pulse position, and pulse frequency were varied from part to part of copies thus produced. Subsequently, such copies were copied in a conventional video machine equipped with tape copying facilities, whereafter the signal obtained from such "pirate copies" was measured in the same manner as the signal obtained from the original.
• circuits which constitute components of the pulse train generator unit 4 of an apparatus according to the invention and which determine the characters frequency, amplitude, duration, and position of the modification signals, whether said circuits are arranged for having an invariable or a variable influence on the signal may be arranged on the basis of well known technique and, of course, in the latter case the control of the variation, at random for instance, of one or more of said characters may. be provided for by means of computer.

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• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Television Signal Processing For Recording (AREA)
• Signal Processing Not Specific To The Method Of Recording And Reproducing (AREA)
• Management Or Editing Of Information On Record Carriers (AREA)

Applications Claiming Priority (2)

Publications (1)

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ID=20365686

Family Applications (1)

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Family Cites Families (2)

• 1986
  • 1986-09-24 SE SE8604024A patent/SE458081B/xx not_active IP Right Cessation
• 1987
  • 1987-09-22 EP EP19870906123 patent/EP0324755A1/en not_active Ceased
  • 1987-09-22 WO PCT/SE1987/000426 patent/WO1988002588A1/en not_active Application Discontinuation
  • 1987-09-22 JP JP50564387A patent/JPH02500709A/ja active Pending
  • 1987-09-22 AU AU79627/87A patent/AU7962787A/en not_active Abandoned
• 1988
  • 1988-05-24 DK DK283688A patent/DK283688D0/da not_active Application Discontinuation

Non-Patent Citations (1)

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