AU701116B2

AU701116B2 - Apparatus and method for preventing unauthorized copying of video signals

Info

Publication number: AU701116B2
Application number: AU17786/97A
Authority: AU
Inventors: Hajime Inoue; Keiji Kanota; Yukio Kubota
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1992-07-24
Filing date: 1997-04-08
Publication date: 1999-01-21
Anticipated expiration: 2013-07-23
Also published as: AU1778697A

Description

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is-~, S F Ref: 243276D1

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

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o000 I 0 ttfta Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: Sony Corporation 7-35, Kitashinagawa C-chome Shinagawa-ku Tokyo

JAPAN

Keiji Kanota, Hajime Inoue and Yukio Kub'ota Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Apparatus and Method for Preventing Unauthorized Copying of Video Signals

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The following statement Is a full description of this invention, including the best method of performing it known to me/us:- APPARATUS AND METHOD FOR PREVENTING .UNAIUTHORIZED COPYIN'G OF VIDEO SIGNALS BACKGROUND OF THE INVENTION 2 This invention relates to a method and apparatus f or preventing copying of video signals which are intended to be copy protected and more particularly is directed to prevention of unauthorized copying of video signals transmitEted or received by a digital video tape recorder (VTR).

There has been proposed a VTR for consumer use in which program information in the form of a video signal and an associated audio signal are recorded in digital form on a magnetic tape. Digital recording of video signals and associated audio signals make it possible for such program information to be reproduced and copied (or "dubbed") onto another tape with little no deterioration in the quality of the siqnal reproduced from the copy tape. There are times, however, when it is desirable to prevent such signals from being recorded. For example, in order to protect the rights of those holding a copyright in the recorded material, copyright protection schemes have been oproposed. in which the digital recording format includes a bit for indicating that copying of the recorded digital video signal is to be inhibited. Such proposed copy protection systems are designed to prevent unauthorized copying of a signal that is transmitted in digital f orm from one digital VTR to another.

With respect to digital V-rRs that can provide analog video and audio output and can receive analog video and audio signals as input signals, transmission of the video and audio

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1 -i fi, i-ii i -2signals in analog form from one digital VTR to another permits the receiving VTR to record a very high quality signal in digital form. The previously proposed copy protection systems for digital VTRs are not effective to prevent a digital VTR from srecording a signal received in analog form, and the high quality of the resulting copies makes such copies a significant threat to the interests of those owning rights in the program information, such as copyright holders.

6o Moreover, there are a number of other sources of o 0a protectable program information in the form of video signals besides analog or digital video outputs from digital VTRs. Among these are television program signals broadcast from conventional terrestrial stations, television programs broadcast from satellites, video signals output from video disk players, television programming distributed by cable, and pay-per-view programming distributed by satellite or by cable. In some cases the broadcast signal may be free of any copyright but in other 0 cases copyright is asserted. It is desirable that copying of the signals be prevented when a copyright is asserted with respect to the material represented by the signal or when the owner of such program information wishes to prevent unauthorized copying thereof.

OBJECTS AND SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention 4i 25 to provide a method and apparatus for ,reventing a digital VTR -3- Another object is to prevent a digital VTR from recording.video signals as to which copyright is asserted.

A further object of this invention is to prevent a digital VTR from recording copy protected'vided6signals which are received in'analog form from a digital VTR or another source of oI video signals..

In accordance with an aspect of the present invention, 10a method of transmitting a video signal includes the steps of forming a digital code that includes at least a copy.protection -bit and category information which identifies a type of device from which the video signal is transmittedi multiplexing the mdltiplexed video signal.

SAccording to -another aspect of the present invention, a video recordin6 apparatus includes structure for receiving a 0multiplexed t video signal which has a verticl blanking interval that includes a digital code containing at least a copy protection bit and category information for identifying the type of15 ntervauipment form which the multiplexed video signal having the digital code transmitted, structure for recblankving terval, audio signal associated the multiplexed vdeoideo signal, a copy protection circt for According to another aspect of the present invention, a video recording apparatus includes structure for receiving a video signal which has a vertical blanking interval that includes a digital code containing at least a copy protection bit and category information for identifying the type of equipment from which the multiplexed video signal was transmitted, structure for receiving an audio signal associated I 25with the multiplexed video signal, a copy protection circiit for -rs i -4determining whether or not copying of the video signal is permitted based on the copy protection bit and the category information, circuitry for recording the received video and audio .signals if it is determined by the copy protection circuit that of the video signal is permitted, and circuitry for inhibiting recording of at least one of the video signal and the audio signal if it is determined by the copy protection circuit that copying of the video signal is not permitted.

.o Acc6rding to further aspects of the invention, the 0o 10 ciccuitry for inhibiting recording includes structure for scrlambling the video signal so that a scrambled video signal is recorded which cannot.be satisfactorily reproduced, and structure °:for muting the audio signal so that the audio signal is not recorded.

-15 The foregoing method and apparatus provide copy oo protection of video signals received in analog form by a digital VTR from another digital VTR- or from other sources of analog video signals.

The above, and other objects, features and advantages of the present invention will be apparent from the following detailed description thereof which is to be read in connection with the accompanying drawings.

tSS St BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of a reproducing section and a recording section of respective digital VTRs which are embodiments of the present invention; Fig. 2 is a waveform diagram which shows the format of an ID signal generated in the VTR reproducing section illustrated in Fig. .1; Fig. 3 is a schematic illustration showing additional details of th& ID signal format of Fig. 2; and p..o 10 Fig. 4 is a block diagram of a video system in which the present invention may be applied.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to Fig. 1. Fig. 1 shows, in block form, 15 a reproducing section 31 of a first digital VTR and a recording *00o o. section 32 of a second digital VTR. In particular, Fig. 1 shows the portions of the reproducing section 31 needed for outputting analog signals, and the portions of recording section 32 needed for making a digital recording from analog input signals.

Reproducing section 31 includes an analog audio output terminal 11 and an analog video output terminal 12. Reproducing section 32 includes an analog audio input terminal 13 and an analog video input terminal 14. As shown in Fig. 1, the audio output terminal 11 of reproducing section 31 is connected to the input tarminal 13 of recording section 32, and the video S6output terminal 12 of reproducing section 31 is connected to the video input terminal 14 of recording section 32.

Reproducing section 31 includes a magnetic tape 1 on which a digital video signal has been recorded in compressed form. The compressed digital video signal is reproduced from magnetic tape 1 by a magnetic head 2 and the reproduced signal is supplied to a data reproduction circuit 3. The reproduced ,o digital signal is provided through the data reproduction circuit 3 to both an audio reproduction circuit 4 and a data expanding 10 circuit 5. The audio reproduction circuit 4 outputs an audio signal which is supplied to a D/A converter 9. The D/A converter 9, in turn, generates an analog audio signal provided for output at audio output terminal 11.

The reproduced signal provided to the data expanding circuit 5 is expanded therein to form an expanded digital video signal which is provided to an adding circuit 8. The reproduced signal output 'from data reproduction circuit 3 is also supplied to a copy guard bit detecting circuit 6. The copy guard bit detecting circuit 6 determines whether copying of the signal recorded on the tape 1 is permitted. This determination is made on the basis of the state of a copy guard bit that is included in the data as recorded on the tape 1. A signal representing the result of the determination is output from the copy guard bit detecting circuit 6 to an ID signal generating circuit 7. On the basis of the output signal fronm the copy guard bit detecting 7 ~IIIIIIP~~ ~b~-bl -7circuit 6, the ID signl generating circuit 7 generates an ID signal which will be described below. The ID signal generated by the ID signal generating circuit 7 is provided to the adding circuit 8, which combines the ID signal with the expanded digital video signal output from data expanding circuit 5 so that the ID signal is inserted into at least one horizontal interval of the vertical blanking interval of the expanded digital video signal. The resulting multiplexed digital video signal, which includes the ID signal; is provided from the adding circuit 8 to a D/A converter 10. D/A converter converts the multiplexed digital video signal into an analog video signal, which is provided as an output signal at video output terminal 12.

1o The ID signal generated by ID signal generating circuit 7 will now be described in more detail with reference to Figs. 2 and 3. Fig. 2 shows a horizontal line :o signal from the vertical blanking interval of the multiplexed video signal output from video output terminal 12. For example, the illustrated line interval may be line 21 or •oooo line 283 of an odd or even field interval, although other line intervals may be used.

The horizontal line signal shown in Fig. 2 includes a reference bit Ref disposed in a time slot near the beginning of the line. This is followed by bits 1 through 20 disposed in corresponding copy guard data time slots, the bits 1 to 20 making up the ID signal.

The reference bit can take up a single slot, as shown, or can take up a plurality of time S.slots. In a preferred embodiment (not shown) the reference signal is a bi-level signal S 20 disposed in plural time slots, the bi-level signal having an initial high-level component followed by a low-level component.

Referring now to Fig. 3, the 20 bits making up the ID signal comprise a word 0 consisting of 6 bits, a word 1 consisting of 4 bits, a word 2 consisting of 4 bits, and a cyclic S1 R .c a ptt ia 8 I r wduhdancy coe (CRC) consispingof bits. Thebits making up !word 0 contain fundamental parameter and identification information with respect to a transmission format for the video signal. One of the bits of word I indicates whether or not copy protection is asserted with respect to the recorded material whether the material is protected by copyright) and another bit included in word 1 indicates whether the recording is an original recording or a copy. For example, the third bit of word i" 1 may be the bit relating to copy protection, with the value "0" S. l10 indicating that copying is to be prevented and value "1" indicating that copy protection is not asserted. Similarly, the fourth bit of word 1 may be used for indicating whether the 'recording is original. For example, if the fourth bit of word I j has the value this may signify that the material is 15 "origial" or proprietary, while the value indicates that the material is commercially available.

The 'four bits of word 2 comprise a category code which identifies the type of device from which the video signal is being transmitted. In the present case, the category code would identify the type of device (consumer digital VTR) of which the reproducing section 31 is a part.

The 6-bit CRC following word 2 is a well-known type of error detection code and is used for detecting errors in the ID signal.

-9- As will be seen, the ID signal can be used to determine whether or not to inhibit copying, with operation of a recording apparatus to be controlled on the basis of the determination.

Referring again to Fig. 1, the analog audio signal from the output terminal 11 and the analog video signal from the output terminal 12 are respectively received at the audio input terminal 13 and th. video input terminal 14 of recording section 32.

The analog audio signal received at audio input o 10 terminal 13 is provided to an A/D converter 15, which converts Q° 4( the analog audio signal into a digital audio signal.. The digital audio signal formed by A/D converter 15 is supplied to an audio recording circuit 17, which outputs a digital audio recording .signal through a switch 23 to an adding circuit 24. The analog, video signal receivediat video input terminal 14 is provided to an A/D converter 16, which converts the received analog video signal into a'-digital video signal. The digital video signal "formed by A/D converter 16 is supplied through a scramble circuit 18 to a bit compression circuit 19. The bit compression circuit 19 compresses and encodes the digital video signal and the resulting compressed and encoded digital video signal is supplied to the adding circuit 24. The compressed and encoded digital video signal and the digital audio recording signal are combined at adding circuit 24 to form a synthesized signal, which is supplied to a data recording circuit 25. A data recording jcigra

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output from data recording circuit 25 is recorded on a magnetic tape 27 by means of a magnetic recording head 26.

The above-mentioned scramble circuit 18 is selectively connected to key generation circuit 21, by means of a switch 22, for receiving a key signal generated by the key generation circuit 21.

An ID detection circuit 20 is connected to receive the digital video signal formed by A/D converter 16 and is also connected to switches 22 and 23 for controlling the operating i. 10 states thereof on the basis of an ID signal detected in the I digital video signal by ID signal detection circuit 20. The ID signal detection circuit 20 determines on the basis of the detected ID signal whether or not copying of the'input video and audio signals is permitted and controls the switches 22 and 23 15 depending on whether copying is permitted. The determination as to whether copying is permitted may be made, for example, according to rules such as the following: If the copy protection bit (bit 3) of word 1 has the value then copying is permitted. If the value of that bit then whether copying is permitted depends on the category code (word if bit 3 of word 1 is and the type of device which is the source of the input signal, as indicated by the tegory code, is a consumer-use digital VTR, then copyi: g is prohibited, but if the source of the input signal is a professional-use digital VTR, then copying is still permitted, even if bit 3 of word 1 is 11 r i I

OR,

operation of recording section 32, for recording the received audio and video signals when copying thereof is permitted, and for inhibiting recording of the signals when copying is not permitted, will now be described.

Let it first be assumed that copying of the received signal is permitte'. In this case, the ID signal detection circuit 20 detects an ID signal, h~aving the format described above with respect to Figs. 2 and 3, in the digital video signa-l formed by A/D-converter 16. The ID signal detection circuit 10 determines, from the copy protection bit (bit 3) of word 1, from the category code (word and possibly also from the "original" bit of word 1, that' copying of the received video and audio signals is permitted. on the basis of the detp~rmination (which for present purposes is assumed to indicate that copying is permitted) the ID signal detection circuit 20 causes, switch 22 to be. in'.an open position and causes switch 23 to be in a closed position.

Because switch 22 is open, no key signal is provided from the key generation circuit 21 to scramble circuit 18, and therefore the digital video signal formed by A/D converter 16 is pr .ovided in unscrambled form f or bit compression by bit compress. ion circuit 19. The resulting unscrambled, compressed digital video signal is then provided to adding circuit 24, which also receives the digital audio recording signal from audio recording circuit 17, because the switch 23 is in its closed 12position. The synthesized signal formed by adding circuit 24 is then provided for recording on magnetic tape 27 through data recording circuit 25 and magnetic head 26, as previously described. As a result, a copy of the audio and video input signals is formed on magnetic tape 27.

Next, let it be assumed that copying of the received video and audio signals is not permitted. As in the previous case, the ID signal detection circuit 20 detects the ID signal in the digital video signal formed by A/D converter 16, but this time ID signal detection circuit 20 determines from the ID signal that copying is not permitted. Based on this determination, ID signal detection circuit 20icauses switch 22 to be closed and switch 23 to be opened.

Because switch 22 is closed, a key signal generated by key generation circuit 21 is provided to scramble circuit 18, which causes the digital video signal provided from A/D converter S16 to be scrambled before it is supplied to bit compression circuit 19. At the same time, the digital audio recording signal formed by aud 4 .o recording circuit 17 is not supplied to the adding circuit 24 because switch 23 is in an open position. In other words, the audio signal is "muted".

As a result, a scrambled digital video signal is recorded on magnetic tape 27 by means of the data recording circuit 25 and the magnetic head 26, the scrambling of the video signal being such that a satisfactory video picture ci 1« iA 13cannot be reproduced and displayed from the signal recorded on the magnetic tape 27. It will also be understood-that no audio signal is recorded on the tape 27.

Thus, in the embodiment of the invention as justdescribed, copying of both an analog video signal and an associated analog audio signal received by.a digital VTR are selectively inhibited on the basis of an ID signal present in a vertical blanking interval of the received analog video signal.

Acdording to alternative embodiments of the invention, 10 only recording of the video signal, or only recording of the audio signal, may be inhibited when the ID signal indicates that copying is not permitted.

According to another alternative embodiment of the Sinvention, both a reproducing section 31 and a recording section 1532, as describeC above in connection with Fig. 1, are incorporated in a single digital VTR, with a single tape '"transport mechanism being shared by the reproducing, section 31 and the recording section 32, the tapes 1 and 27 therefore being one and the amie, and the respective output terminals 11 and 12 input terminals 13 and 14 not being interconnected.

According to this embodiment, the reproducing section 31 operates to output to further apparatus a multiplexed analog video signal having an ID signal inserted in the vertical blanking interval of the video signal as described in connection with Figs. 2 and 3.

the recording section 32 includes the ID signal detection i i.

i- -14circuit 20 and the other circuitry for inhibiting recording by this embodiment in accordance with an ID signal that is present in a multiplexed analog video signal that is received by this embodiment. It will be appreciated that this embodiment provides both ID signal generation and selective inhibition of recording, S.depending upon whether this embodiment is operating in a playback or recording mode. Accordingly, this embodiment is suitable for distribution to consumers as part of a copy protection system.

"The-present invention may also be embodied in a 10 multiple-deck digital VTR incorporating all of the circuitry illustrated in Fig. 1, and with respective connections between analog audio input and output terminals and analog video input.

and output terminals, so that dubbing can be performed within the multiple-deck VTR by simultaneously using two tape transport decks. In this embodiment, such dubbing operations will be inhibited:if the ID signal formed in the reproducing section indicates that.copying is not permitted.

Selective inhibition of copying by a digital VTR in accordance with the invention can also be carried out in a system which a digital VTR receives input video signals from sources in-addition to another digital VTR.

For example, Fig. 4 shows a video system that includes a digital VTR 50 which has at least the recording section 32 as shown in Fig. 1 and another digital VTR 53 which has at least the 1 25reproducing section 31 as shown in Fig. 1. VTRs 50 and 53 are I V connected so that VTR 53 is a source of analog video and audio signals for VTR 50. Moreover, VTR 50 is also connected to receive analog video and audio input from a. conventional VHF/UHF tuning receiver 51, and from a video disk player 52. The videodisk player 52 may include, in accordance with,.the present invention, reproducing circuitry similar to the reproducing section 31 'of Fig. 1, and including an ID signal generation Scircuit as described in conection with Figs. 1-3.

A pay-per-view and/or pre-paid subscription cable receiving system made up of a cable T.V. tuner 54 and a cable.

ST.'V. decoder 55 also is a source of analog video and audio input signals for VTR 50, as is a satellite broadcast receiving system made up of a satellite broadcasting tuner 56 and a decoder 57.

The ID signal generation and multiplexing functions described 15with respect to-reproducing section 31 of Fig. 1 are, in i.c, accordance with the invention, included in the decoders 55-and 57 so that copying of the signals provided by the dbcoders 55 and 57 to the VTR 50 can be selectively inhibited on the basis of the ID signals generated in decoders 55 and 57.

It will be appreciated that an ID signal according to tle format shown in Figs. 2 and 3 may also be included in a multiplexed analog video signal broadcast from a terrestrial broadcasting station and received via tuner 51.

Therefore, in the embodiment of Fig. 4 selective of recording by VTR 50 of analog video signals I 16supplied thereto from a variety of sources can be accomplished in accordance with ID signals present in the input video signals.

Having described specific preferred embodiments of the j present invention with reference to the accompanying drawings, it to be understood that the invention is not limited to those precise embodiments, and that various changes.aid modifications I may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims. For example, although reproducing section 1031 and recording section 32 have been shown and described with S. D/A and A/D converters so that analog signals are transmitted and received, such D/A and A/D conversion may be pmitted, and digital video signals having the ID signal in the vertical blanking interval may be transmitted and received directly.

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Claims

1. A method of transmitting a video signal comprising the steps of: forming a digital code including copy guard data operable to inhibit recording equipment from recording a viewable video signal when said video signal contains said copy guard data; mul.iplexing said digital code with a video signal having a vertical blanking interval to form a multiplexed video signal having said digital code in said vertical blanking interval; and transmitting said multiplexed video signal in the form of an analog signal.

2. The method according to claim 1, wherein said digital code is comprised of copy guard data time slots in which said copy guard data is provided, and said digital code further includes a reference signal disposed in at least one time slot ""which precedes said copy guard data time slots.

3. The method according to claim 2, wherein said reference signal is disposed in plural time slots.

4. The method according to claim 3, wherein said reference signal is a :.bi-level signal having a relatively high level in a first preceding time slot and relatively low level in an immediately succeeding time slot.

5. The method according to any one of claims 1 to 4, wherein said copy Sa 20 guard data comprises at least a copy protection bit and category information that So* identifies a type of device from which the video signal is transmitted.

6. A video recording apparatus, comprising: means for receiving a multiplexed video signal in the form of at. analog signal having a vertical blanking interval that includes a digital code including copy guard data operable to inhibit said video recording apparatus from recording a viewable video signal when said video signal contains said copy guard data, the copy guard data comprising at least a copy protection bit and category information that identifies a type of device from which the video signal is transmitted; means for receiving an audio signal associated with said multiplexed video signal; i P_1 11 -18- -1 8- ;dJ means for determining whether or not copying of said video signal is permitted based on said copy protection bit and said category information; means for recording the received video and audio signals if it is determined by said means for determining that copying of said video signal is permitted; and means for inhibiting recording of at least one of said video signal and said audio signal if it is determined by said means for determining that copying of said video signal is not permitted.

7. The video recording apparatus according to claim 6 wherein said digital code is comprised of copy guard data time slots in which said copy guard data is provide6, and said digital code further includes a reference signal disposed in at least 000 O 0o one time slot which precedes said copy guard time slots. o00

8. The video recording apparatus according to claim 7, wherein said ro reference signal is disposed in plural time slots.

9. The video recording apparatus according to claim 8, wherein said reference signal is a bi-level signal having a relatively high level in a first preceding :0 0 time slot and a relatively low level in an immediate succeeding time slot. :o0

10. The video recording apparatus according to any one of claimns 6 to 9, too. wherein said copy guard data contains at least a copy protection bit and category information for identifying a type of equipment from which the multiplexed video signal was transmitted.

11. The video recording apparatus according to claim 10, wherein said means for recording includes means for recording the received video and audio signals on a record medium.

12. The video recording apparatus according to claim 10, wherein the received audio signal is an analog signal and further comprising means for converting said received video and audio signals to digital video and audio signals, said digital signals being recorded by said means for recording. N:';bccjOO826ayl -19-

13. The video recording apparatus according to claim 10, wherein said means for inhibiting includes means for scrambling said video signal so that said means for recording records a scrambled video signal from which a video picture cannot be satisfactorily displayed.

14. The video recording apparatus according to claim 10, wherein said means for inhibiting includes means for muting said audio signal so that said audio signal is not recorded.

The video recording apparatus according to claim 10, further i comprising: means for reproducing a digital video signal from a record medium; means for detecting said copy guard data that is present in said reproduced digital video signal; .00. means for outputgenerating an ID signal in accordance with the detected copy guardexed digital video signa o1-

16. The video recording apparatus according to claim 15, wherein said i 1s means for inserting said ID signal into a vertical blanking period of said m reproduced digital video signal isto form a multiplexed digital video sigsig nal, and furthean comprising means for outputting said multiplexed digital video signal.

17. The video recording apparatus according to claim 15, wherein said means for outputting said multiplexed digital video signal includes means for converting said multiplexed digital video signal into an analog video signal having said ID signal in a vertical blanking interval thereof.

18. The video recording apparatus according to claim 7, further comprising: means for reproducing a digital video signal from a record medium; 20 means for converting said reproduced digital video signal into an analog video signal; means for detecting said copy guard data that is present in said reproduced digital video signal; means for generating an ID signal in accordance with the detected copy guard data; means for inserting said ID signal into a vertical blanking period of said analog video signal; and means for outputting said analog video signal having said ID signal inserted in said vertical blanking period of said analog video signal.

19. The video recording apparatus according to claim 18, wherein said reproduced digital video signal is a compressed digital video signal, and further "comprising means for expanding said compressed digital video signal.

A method of recording a video signal comprising the steps of: receiving a multiplexed video signal in the form of an analog signal having a ,vertical blanking interval that includes a digital code containing copy guard data to inhibit recording equipment from recording a viewable video signal when said video signal contains said copy guard data, the copy guard data including at least a copy protection bit and category information that identifies a type of device from which the 84 44 o video signal is transmitted; *u receiving an audio signal associated with said multiplexed video signal; determining whether or not copying of said video signal is permitted based on said copy protection bit and said category information; recording the received video and audio signals if it is determined by said means for determining that copying of said video signal is permitted; and inhibiting recording of at least one of said video signal and said audio signal if it is determined by said means for determining that copying of said video signal is not permitted.

21. The method according to claim 20, wherein said digital code is 4,3o comprised of copy guard time slots in which said copy guard data is provided, and said IN:\ULIBEIO1027;MXL -21 digital code further includes a reference signal Isposed in at least one time slot which precedes said copy guard data time slots.

22. The method according to claim 21, wherein said reference signal is disposed in plural time slots.

23. The method according to claim 22, wherein said reference signal is a bi-level signal having a relatively high level in a first preceding time slot and relatively low level in an immediately succeeding time slot.

24. The method according to any one of claims 20 to 23, wherein said copy guard data contains at least a copy protection bit and category information for 10 identifying a type of equipment from which the multiplexed video signal was *ot. transmitted.

25. The method according to claim 24, wherein said recording step S includes recording the received video and audio signals on a record medium.

26. The method according to claim 24, wherein the received audio signal 15 is an analog signal and further comprising the step of converting said received video and audio signals to digital video and audio signals, said recording step including recording said digital signals.

27. The method according to claim 24, wherein said inhibiting step includes scrambling said video signal so that said recorded video signal is a scrambled video signal from which a video picture cannot be satisfactorily displayed.

28. The method according to claim 24, wherein said inhibiting step includes muting said audio signal so that said audio signal is not recorded.

29. An apparatus for transmitting a video signal, comprising: means for forming a digital code including copy guard data operable to inhibit recording equipment from recording a viewable video signal when said video signal contains said copy guard data; Fl-22- rmeans for multiplexing said digital code with said video signal having a vertical blanking interval to form a multiplexed video signal having said digital code in said vertical blanking interval; and means for transmitting said multiplexed video signal in the form of an analog signal.

The apparatus according to claim 29, wherein said digital code is comprised of copy guard data time slots in which said copy guard data is provided, and said digital code further includes a reference signal disposed in at least one time slot which precedes said copy guard time slots.

31. The apparatus according to claim 30, wherein said reference signal is disposed in plural time slots.

32. The apparatus according to claim 31, wherein said reference signal is K *a bi-level signal having a relatively high level in a first preceding time slot and a relatively low level in an immediate succeeding time slot.

33. The apparatus according to any one of claims 29 to 32, wherein said V copy guard data includes at least a copy protection bit and category information that 1 ,identifies a type of device from which the video signal is transmitted. 1,

'34. An apparatus for transmitting and receiving a video signal, comprising: 2o means for forming a digital code that includes copy guard data operable to inhibit recording equipment from recording a viewable video signal when said video signal contains said copy guard data; means for multiplexing said digital code with a video signal having a vertical blanking interval to form a multiplexed video signal having said digital code in said vertical blanking interval; means for transmitting said multiplexed video signal; I- S-23- means for receiving said multiplexed video signal that was transmitted by said means for transmitting, wherein said multiplexed video signal is transmitted and i|i received in the form of an analog signal; and means for determining whether or not copying of said received video signal is permitted based on said copy guard data contained in said vertical blanking interval of J said received video signal. I

35. The apparatus according to claim 34, wherein said digital code is comprised of copy guard data time slots in which said copy guard data is provided, and said digital code further includes a reference signal disposed in at least one time slot which precedes said copy guard time slots.

36. The apparatus according to claim 35, wherein said reference signal is disposed in plurai time slots.

37. The apparatus according to claim 36, wherein said reference signal is a bi-level signal having a relatively high level in a first preceding time slot and a S" 15 relatively low le\ an immediate succeeding time slot.

38. The apparatus according to any one of claims 34 to 37, wherein said ;,to copy guard data includes at least a copy protection bit and category information which identifies a type of device from which the video signal is transmitted. o

39. A method of transmitting and receiving a video signal comprising the steps of: forming a digital code that includes copy guard data operable to inhibit recording equipment from recording a viewable video signal when said video signal contains said copy guard data; multiplexing said digital code with a video signal having a vertical blanking interval to form a multiplexed video signal having said digital code in said vertical blanking interval; transmitting said multiplexing video signal; -24- receiving said transmitted multiplexed video signal, wherein said multiplexed video signal is transmitted and received in the form of an analog signal; and determining whether or not copying of said received video signal is permitted based on said copy guard data contained in said vertical blanking interval of said received video signal. The method according to claim 39, wherein said digital code is comprised of copy guard data time slots in which said copy guard data is provided, and said digital code further includes a reference signal disposed in at least one time slot which precedes said copy guard data time slots. 1o 41. The method according to claim 40, wherein said reference signal is s ado disposed in plural time slots. i 1:0. 42. The method according to claim 41, wherein said reference signal is a Sbi-level signal iaving a relatively high level in a first preceding time slot and relatively low level in an immediately succeeding time slot. io.. 15 43. The method according to any one of claims 39 to 42, wherein said S• copy guard data includes at least a copy protection bit and category information which 15 4DATED this EIGHTH day of APRIL 1997 Sony Corporation Patent Attorneys for the Applicant SPRUSON FERGUSON I 1 Vl~ I Apparatus and Method for Preventing Unauthorized Copying of Video Signals ABSTRACT In a digital video tape recorder (53) which reproduces digital video and audio signals from a magnetic tape, a copy protect bit. in the reproduced ditigal video signal is detected, and on the basis of the copy protect bit, a code is generated and inserted into the vertical blanking interval of the reproduced video signal When a video signal (which may be in analog or ditial form) having the code in the vertical blanking interval is received in a digital VTR the code is detected and recording of the video signal and an associated audio signal is inhibited if the code indicates that the received video signal is copy protected. fi: 1.. t a ~w ta j* a f I 4)~I 'I. i