HK1099873B - An apparatus and a method of providing a serial copy protection scheme for a digital video signal - Google Patents

Description

Method and apparatus for providing a continuous copy protection scheme for digital video signals

This application is a divisional application of an invention patent application having an application date of 1994, 3/4, application number of 200410002418.2, entitled "method for copy protecting a video signal composed of a digital data bit stream".

Technical Field

The invention aims to disclose a copy protection method and equipment, which are used for: (1) digital television recordings in which copy protection of analog and digital video signals associated with digital recording or playback equipment is required; (2) any video material for which the original source material is not copy protected.

Background

There are many known techniques for video signal copy protection schemes, including U.S. patent No. 4,631,603, which is assigned to John o.ryan on 12/23 1986 and is assigned to Macrovision, which aims to modify an analog video signal to inhibit recording of an acceptable video signal therefrom by adding pulse pairs to another unused line of the vertical blanking period of the video signal, each pulse pair comprising a negative going pulse followed by a positive going pulse which acts to interfere with the AGC (automatic gain control) of a VCR (video cassette recorder) which records such a signal, so that when the recorded signal is played back, the recorded signal is not visible due to the presence of a very large black image.

Another analog video signal protection scheme is disclosed in U.S. patent 4,914,694 issued to Leonard at 4/3 1990 and assigned to Eidak, incorporated herein by reference. The Eidak system (see abstract) increases or decreases the standard length of each field of the video signal by either maintaining a constant, standard number of lines per frame and varying the duration of the corresponding horizontal line period in each field, or by maintaining a standard duration of each line period and varying the number of horizontal line periods making up a frame.

These video protection systems modify the video signal to be recorded (e.g., on tape) or to be broadcast (e.g., protected pay tv programs) so that copying with normal VCRs is difficult or impossible. When a video tape on which a copy-protected video signal is recorded is played back with a VCR for viewing, the copy protection process is substantially noticeable, i.e., does not affect the viewing experience. However, any attempt to reproduce the video signal on the tape using a second VCR to record the output of the first (playback) VCR will necessarily result in a reduction in image quality to a degree which is related to the efficacy of the particular copy protection system. These existing video copy protection systems only protect analog video signals, which are the type of video signals broadcast and recorded using current consumer video recording technology.

Digital video tape recorders are also known, but these digital video tape recorders (i.e. digital both recording and playback) are only available to the professional market due to their high price. Such digital systems trade natural (free) distortion characteristics for higher bandwidth, i.e. more information must be recorded per video frame. The digital video recorder has an advantage for users that each successive copy does not cause a significant degradation of image quality as long as the signal is recorded and reproduced in the digital domain, unlike the conventional analog recording technique. Current digital video recorders (not used for consumer purposes) employ the so-called "D-1", "D-2" or "D-3" video recording standard and require special video tapes.

It is widely believed that digital video tape recorders will soon land on the commercial consumer market. In order to remain compatible with analog video broadcast signals and analog video tape recorders, it is likely that at least the first generation consumer digital video tape recorders will be "hybrid" digital and analog systems.

Such a system would have the ability of current analog video cassette recorders to record and play back analog signals while having comparable digital capabilities. Thus, these new hybrid digital video tape recorders will be able to internally convert an input analog signal to a digital signal and record the digital signal on a magnetic tape as a digital data stream. During playback, the digital data stream on the tape can either be displayed as a digital signal by a digital television (not currently available) or be reconverted to a conventional analog video signal (such as an NTSC signal for the united states) within the hybrid video tape recorder. The ability to convert received analog signals into digital data streams within the system is important because digital video program material sources (tapes or broadcasts) are not currently available to consumers.

Such hybrid video recorders may possibly take on "consumer" digital recording formats that are not the same as the standards of current professional digital systems. Such consumer digital video signal formats have not been established. As with currently common analog VCRs, such digital video recorders may include a conventional "front-end" RF tuner and an RF modulator on the output side. (by analog video signal, we mean here NTSC, PAL or SECAM.) the digital recording standard for consumers may be essentially a data structure representing the video signal as a (binary) data bit stream with appropriate error concealment coding and actual tape standard tracks.

Since digital video tape recorders can reproduce with high fidelity, i.e. have the potential to stimulate human reproduction, it is important to design such recorders for consumer use to inhibit or prevent illegal recording. For example, it is important to prevent the illegal copying of copyrighted video material using a video recorder, and also to prevent the playback of such illegally copied material. The analog video copy protection techniques used today are not applicable in the digital domain.

There is therefore a need for a new copy protection system suitable for use in such hybrid digital and analog video tape recorders in which the material recorded on the tape is a digital data stream. A typical situation to be prevented is to use a hybrid video tape recorder to copy the output signal from a conventional VHRVCR, where there is a conventional copy protection process on the tape played back from the VHRVCR, the problem being to prevent new hybrid digital-mode video tape recorders from copying data from such tape. Otherwise, the presence of such a hybrid recorder would encourage copyright infringement.

In german patent 4,015,626 to Mitsubishi, a still frame video recorder is disclosed which employs copy protection techniques of a digital tape (DAT) recorder playback system, but an analog copy protection scheme is not included in the disclosed analog output apparatus which provides for recording of still frame image video signals, but not moving image video signals.

In european patent 0,392,612 to n.v. philip, an audio signal copy protection technique is disclosed which is not suitable for the presently claimed system, since the system only employs the audio signal copy protection technique, and does not have digital copy protection. The analog and video signal mixing system will be described below, and for any digital television recording and playback mechanism, it is necessary to have analog and digital input and output mechanisms suitable for copy protection techniques.

Disclosure of Invention

It is an object of the present invention to provide a method of copy protecting a video signal formed of a digital data bit stream, the method employing a continuous copy protection bit detector comprising: setting a first continuous copy protection bit to a predetermined value, the first continuous copy protection bit appearing at a pre-specified position in the bitstream; determining a value of a first continuous copy protection bit upon receiving the video signal in the continuous copy protection bit detector; upon determining that the value of the first continuous copy protection bit is a predetermined value, setting a second continuous copy protection bit to a predetermined value, wherein the second continuous copy protection bit is located at a position in the bitstream associated with the first continuous copy protection bit; detecting a second continuous copy protection bit; and recording of the video signal is disabled upon detection of the second continuous copy protection bit.

The method according to the invention further comprises: a number of first and second consecutive copy protection bits are set that occur periodically in the bitstream.

A hybrid digital and analog tape recorder that records digitally provides copy protection in both the digital and analog domains. For an externally supplied analog video signal, the recorder detects the presence of copy protection and therefore disables recording; for an externally supplied digital video signal, detecting a copy protection bit and a continuous copy protection bit to (1) inhibit recording and (2) prevent a subsequent copying by a second digital recorder, respectively; for reproducing recorded material, the presence of copy protection bits is detected in the digital reproduced video signal and the digital reproduced video signal is modified by an analog video signal copy protection process once converted to an analog signal.

In another embodiment, video material from an analog or digital source (either pre-recorded or from an external source) is provided with a copy protection flag. Detection of the mark by the playback device results in an analog copy protection process that modifies the standard video signal being played back. This embodiment is applicable to a playback apparatus in which a video signal source cannot be copy protected, but a standard (NTSC) video signal is recorded for playback.

The present invention also provides a method of providing a continuous copy protection scheme for a digital video signal comprising a digital video bit stream including continuous copy protection scheme bits, including a continuous copy protection scheme bit reader or detector and a copy protection bit adder, the method comprising: providing a digital video bit stream to a continuous copy protection scheme bit reader or detector; outputting a start signal for starting the anti-copy bit adder from the continuous copy protection scheme bit reader or the detector if the continuous copy protection scheme bit is detected; adding, by the anti-copy bit adder, an anti-copy bit to a predetermined position of the digital video signal in response to the start signal; reading or detecting an anti-copy bit in the digital video signal to provide a control signal; adding a digital copy protection signal to the digital video signal in response to the control signal; and converting the digital video signal and the digital copy protection signal into an analog video signal containing the analog copy protection signal.

The present invention also provides a method of providing a continuous copy protection scheme for a digital video signal comprising a digital video bit stream including continuous copy protection scheme bits, including a continuous copy protection scheme bit reader or detector and a copy protection bit adder, the method comprising: providing a digital video bit stream to a continuous copy protection scheme bit reader or detector; generating, by a continuous copy protection scheme bit reader or detector, an enable signal for enabling the anti-copy bit adder if the continuous copy protection scheme bit is detected; adding an anti-copy bit to a predetermined position in the digital video signal in response to the start signal; detecting an anti-copy bit in the digital video signal; converting the digital video signal into an analog video signal; and adding an analog copy protection signal to the analog video signal in response to the detected copy protection bit.

The present invention also provides a method of providing a continuous copy protection scheme for a digital video signal consisting of a digital video bit stream containing continuous copy protection bits, wherein a continuous copy protection signal reader or detector and a copy protection bit adder are provided, the method comprising: coupling a digital video bitstream to a continuous copy protection signal reader or detector; wherein if the continuous copy protection scheme bit is detected, the continuous copy protection signal reader or detector outputs a start signal to start the anti-copy bit adder; whereby, in response to the continuous copy protection signal reader or detector, a copy protection bit is added to a predetermined position of the digital video signal; reading or detecting an anti-copy bit in the digital video signal to provide a control signal; adding a digital copy protection signal to the digital video signal in response to the control signal; and converting the digital video signal and the digital copy protection signal into an analog video signal containing the analog copy protection signal.

The present invention also provides an apparatus for providing a continuous copy protection scheme for a digital video signal composed of a digital video bit stream containing continuous copy protection scheme bits, comprising a continuous copy protection scheme bit reader or detector and a copy protection bit adder, the apparatus comprising: means for providing a digital video bit stream to a continuous copy protection scheme bit reader or detector; means for outputting an enable signal to enable the copy protection bit adder from the continuous copy protection scheme bit reader or detector; wherein the copy prevention bit is added to a predetermined position of the digital video signal by the copy prevention bit adder in response to the start signal; second means for reading or detecting an anti-copy bit in the digital video signal to provide a control signal; means for adding a digital copy protection signal to the digital video signal in response to the control signal; and means for converting the digital video signal and the digital copy protection signal into an analog video signal comprising an analog copy protection signal.

The present invention also provides an apparatus for providing a continuous copy protection scheme for a digital video signal composed of a digital video bit stream containing continuous copy protection bits, wherein a continuous copy protection signal reader or detector circuit and a copy protection bit adder circuit are provided, the apparatus comprising: circuitry for coupling the digital video bit stream to a continuous copy protection signal reader or detector circuit; wherein if a Sequential Copy Protection Scheme (SCPS) bit is detected, an output of the sequential copy protection signal reader or detector circuit outputs an enable signal; an anti-copy bit adder circuit for adding an anti-copy bit to a predetermined position of the digital video signal in response to the continuous copy protection signal reader or detector circuit; a circuit for reading or detecting the copy protection bit in the digital video signal to provide a control signal; a circuit for adding a digital copy protection signal to the digital video signal in response to a control signal; and a circuit for converting the digital video signal and the digital copy protection signal into an analog video signal containing the analog copy protection signal.

The present invention also provides an apparatus for providing a continuous copy protection scheme for a digital video signal consisting of a digital video bit stream containing continuous copy protection bits, comprising: a continuous copy protection signal reader or detector for outputting an enable signal in response to detection of a continuous copy protection bit; a copy protection bit adder for adding a copy protection bit to a predetermined position of the digital video signal in response to the start signal to provide a continuous copy protection scheme; a second detector for detecting the copy protection bit; circuitry for providing an analog video playback signal; and a copy protection generator for providing a copy protection signal in response to the detected copy protection bit, and for modifying the analog video playback signal in response to the copy protection signal.

Drawings

Fig. 1 is a block diagram of a hybrid digital video recorder according to the present invention.

Fig. 2 is a block diagram of another video recorder or playback apparatus according to a second embodiment of the present invention.

Detailed Description

Fig. 1 shows a hybrid digital-to-analog video recorder according to the invention. Each block includes conventional elements that are currently available on the market or readily made by one of ordinary skill in the art in light of the following description. One possible exception is the digital tape electromechanical architecture that constitutes the main subsystem of this device. Current professional digital video recorders include such tape electromechanical structures, however, they are designed for recording and playing back the relevant material under the current professional digital video standards. Digital tape drive 10 may be of the type included in professional systems currently in such commercialization. However, since it is envisaged that the hybrid system shown in fig. 1 is primarily (but not exclusively) intended for consumers, such a system may include different digital tape electromechanical mechanisms of a type that would be suitable for mass production at low prices and designed according to consumer digital video formats that have not yet been established.

In any event, the video recorder of FIG. 1 may be constructed of presently available elements, including specialized digital tape mechanisms, which are now commercially available from a number of companies. The magnetic tape placed on the magnetic tape drive 10 has the following type (1) video cassette recorder (2) disc recorder.

The recorder of fig. 1 is of a type capable of accepting a conventional analog video signal, indicated by "a", at input 12, which is an NTSC or other signal.

Also shown on the "input" side in fig. 1 is a digital video signal input 14 for receiving a digital video signal (denoted by "D") from an external source. When the broadcast digital video signal is to be broadcast as a commercial broadcast in the future, the terminal 14a receives the signal, and it can also receive the broadcast digital video signal from another digital video recorder or digital playback apparatus.

Since the apparatus of fig. 1 records digital signals, the analog video signal at terminal 12 is converted to the desired digital format by an analog-to-digital converter 16, which is well known in the video signal art, the details of construction of analog-to-digital converter 16 being determined by the characteristics of the digital recording format with which digital tape drive 10 is compatible.

The digital video data stream output by analog converter 16 is provided (via switch 18) to digital tape drive 10. The person (or machine) operating the video recorder of fig. 1 determines whether at any one time he is recording an analog video input signal at terminal 12 or a digital video input signal at terminal 14. Switch 18 (which may be either automatically or manually controlled) selects which of terminals 12 or 14 tape drive 10 receives an input signal to be recorded from.

The input signal from switch 18 is then digitally recorded on magnetic tape by tape drive 10 (not shown). The recorded material on the tape is then played back by the tape drive 10 to produce a digital signal "D" at the output 20 of the tape drive 10. The digital signal at terminal 20 (if the terminal output signal of the video recorder is an analog signal) is supplied to a digital-to-analog converter 22 which converts the digital signal D into an analog output signal a which is supplied to an analog output 24. The digital-to-analog converter 22 (as well as its complementary converter 16) is conventional and its detailed structure is determined by the digital recording format and the analog output format. The analog output 24 is connected, for example, to the "output" side of a recorder to a conventional television set.

The recorder of fig. 1 may typically be provided with an RF tuner (not shown) on the "input" side to derive video signals (NTSC or other) from RF modulated video (TV) signals.

Similarly, an RF modulator (not shown) may be provided on the "output" side to convert a baseband (NTSC or other) video signal at terminal 24 to an RF modulated video signal (TV) for supply to the antenna input of the television set.

The copy protection portion of the apparatus of fig. 1 (when operating in the analog domain) is described with reference to the analog channel described above, which includes analog video input 12, converter 16, switch 18, converter 22 and analog output 24. It is assumed that the (NTSC) analog video received at terminal 12 has been copy protected by a copy protection process as described above, typically by adding a copy protection pulse to the video signal or modifying a particular portion of the video signal. The particular approach is to prevent copying of such material by the recorder of fig. 1 through built-in circuitry, i.e. features built into the recorder by the manufacturer.

One system for conditioning a video recorder to prevent copying of a copy protected video signal is described in us patent 4,907,093 issued to John (o.ryan, and assigned to Macrovision corporation) on 3, 6 of 1990, which patent is incorporated herein by reference as if fully set forth below.

The video signal is modified so that the television receiver still has a normal color image for the video tape recorder to detect and inhibit it from being recorded. Several sequential pseudo-sync pairs and positive pulse pairs are added to the vertical blanking interval of the video signal following the normal sync pulse.

A disabling circuit associated with the video recorder detects the modified signal by comparing the voltage difference between the pseudo-sync tip and the positive pulse with respect to the normal voltage difference between the sync tip and the trailing edge of the blanking period. Modified signals, on the other hand, may be detected by identifying the pulse frequency of the blanking period signals. When the modified signal is present, a control signal is generated to disable the recording device. If no modified signal is detected, the recording device is started.

The recorder of fig. 1 includes a similar copy protection mechanism at the upper left, including an ACP (copy protection process) detector 26, which is similar to the detection circuit described in the embodiments of us4,907,093, and which may also be a detector used in us4,914,694 to detect the copy protection process. The ACP detector 26 may also detect a continuous type of copy protection processing. ACP detector 26 detects the presence of copy protection when an analog (NTSC) video signal is received at terminal 12 and, upon detection, generates a record disable control signal on line 18 to disable, for example, analog-to-digital converter 16.

The inhibit converter 16 is different from the inhibit method described in us patent 4,907,093 (where there is no analog-to-digital converter), in which case some other feature of the recorder is inhibited. As described in us patent 4,907,093, in the recorder of fig. 1, a component other than the analog-to-digital converter 16 may be disabled by a record disable signal on line 28. For example, digital tape drive 10 may be disabled or an additional switch (not shown) in the signal path may be forced to an open position. Other measures for disabling the recorder will be apparent to those skilled in the art, in any case the detection of a copy protection signal in the incoming analogue video signal will disable the recording of that signal.

(the ACP detector 26 here corresponds to the disabling circuit 22a in fig. 1 of the above-referenced patent).

In another case, for recording of copy protected material, the input signal is a digital video signal provided at the digital input video terminal 14. In this case, if the input signal is copy protected, typically such copy protection is provided by a tape copy apparatus setting a predetermined anti-copy control bit in a digital data stream recorded on a tape.

This anti-copy bit will be placed, for example, at a specific location (e.g., a location corresponding to the vertical blanking period) of each video frame. Alternatively, such an anti-copy bit may be placed at a predetermined position in each video line or at some other predetermined portion of the video signal; the exact location of the copy-protection bit is of no particular importance as long as this bit is determined by an accepted standard before the recorder of fig. 1 is manufactured. Therefore, the recorder manufacturer designs a copy protection (AC) bit detector 32 to place the copy protection bit by knowing its numerical address.

Thus, for example, if the anti-copy bit detector 32 detects that the anti-copy bit is set high, i.e., has a value of 1, then it is interpreted as indicating that the associated digital video material cannot be copied. Whereby the copy protection bit detector 32 issues a record disable control signal on line 36 that controls the operation of switch 38. In this case, the record inhibit signal on line 36 opens switch 38, preventing the transfer of the digital video signal from terminal 14 to switch 18. Thus, the anti-copy bit performs the function of inhibiting copying of the associated video material input to the recorder at the digital input 14.

Alternatively, a user of the recorder of fig. 1 may play back material from a prerecorded tape.

In this case, the problem to be solved is to prevent or inhibit the subsequent unauthorized recording and playback of the material. If material reproduced from a magnetic tape on the digital tape drive 10 is supplied from the output 20 to a digital video output 42 (in the digital domain), such subsequent unauthorized recording is not a problem, since then the digital video output signal can only be recorded on another digital video recorder, which is also provided with the copy protection bit detector 32 and associated disabling circuitry.

However, the hybrid recorder of fig. 1 presents an additional copy protection problem providing an analog video output onto terminal 24. The presence of the anti-copy bit in the digital data stream at terminal 20 has no effect on the analog output signal at terminal 24 (has been removed or ignored in the digital-to-analog conversion). Therefore, a copy protection (AC) bit detector 46 is provided in the analog output circuit at the upper right of fig. 1. The AC bit detector 46 is similar to the AC duplicate bit detector 32 and operates in the digital domain to detect the anti-duplicate bits at predetermined locations. An enable signal is sent on line 52 to an anti-copy process (ACP) signal generator 50 in response to the anti-copy bit detected by the AC bit detector 46.

The ACP signal generator 50 is shown in one form in fig. 2 of U.S. patent 4,631,603, and generates an analog video copy protection signal. The ACP signal generator 50 then applies this analog copy protection signal to the output signal of the digital-to-analog converter 22, which has converted the digital output signal of the tape drive 10 to an analog (e.g., NTSC) signal. The ACP signal generator 50, on the other hand, is shown in fig. 1 of the above-mentioned U.S. patent 4,914,694 for modifying a "TV signal source". Thus, the analog (NTSC) video signal at output 24 is an analog video signal modified by the analog copy protection process, thereby achieving the objective of inhibiting the previously recorded tape-provided signal from acceptable video signal recording on existing analog VCRs.

Fig. 1 also includes an SCPS bit detector 54, lines 58, and an AC bit adder 60. In the field of digital tape recording, it is known that a continuous copy management system (SCMS) employs commercially available DAT (digital tape) recorders for deterring (under certain conditions) copying of digitally recorded audio material. SCMS is commonly made by the manufacturer of digital recorders and the providers of digitally recorded program material to restrict copying of such material only in the digital domain. SCMS is described, for example, in reference US 5,144,658. Briefly, the SCMS periodically adds a special control bit to a digital audio recording to be copy protected (usually copyrighted material). In conventional digital audio playback devices, such as CD players, which generate an analog output signal together with a digital output signal, the analog output signal is not copy protected, i.e. control bits or equivalent analog signals are not present therein. That is, the control bits are discarded from the inside by the digital-analog converter processing, and therefore, arbitrary copying can be performed by connecting the analog output of the CD player to the analog tape recorder.

However, the digital output signal of the CD player has the SCMS bit set (high) by the reproducing means of the recorded audio material. The digital tape recorder receiving the digital output signal detects the SCMS bit and, if it is detected, for example, that a bit at a particular location is high, the digital tape recorder will record the material (i.e., digitally record) and, during such recording, will internally expand the bit, for example, with a second bit at a second location. Thus, the tape can be subsequently played back with an acceptable analog output signal or an acceptable digital output signal. However, if a subsequent attempt is made to re-record the tape using another DAT recorder, the second DAT recorder looks for the location of the two bits, and if the second bit is detected, it does not make a copy. Thus enabling a continuous kind of replication in the digital domain from a specific source recording. It is well known that such a system can be easily extended to allow two, three, four or a myriad of copies, as long as continuous copying is required. But its purpose is to limit the number of successive copies to a particular number, usually one in the case of SCMS.

The inventors have determined that a similar continuous copy restriction system is advantageous in the field of digital video.

In the context of the present invention, such a continuous copy restriction system standard has not been defined, but is generally described herein as a "continuous copy protection scheme" (SCPS), contained in the SCPS bit detector 54. SCPS is conceptually similar to SCMS, but belongs to the video category. The SCPS bit detector 54 detects whether a continuous copy protection scheme bit is present in the digital video signal at terminal 14. If the first such SCPS bit is detected, an enable signal is generated on line 58 which controls an AC (copy protection) bit adder 60 which adds (or sets high) a second (actual copy protection) bit at a predetermined position in the digital stream. Such SCPS bits may be placed on equivalent lines such as lines not used in the vertical blanking period.

The video signal is then passed to switch 38 and to digital tape drive 10 via switch 18. Such a digital signal containing the set (high level) copy protection bit is therefore provided to the digital video output 42 via the terminal 20 on subsequent playback.

Providers of video material (e.g., commercial tape replicators, broadcasters, or cable television systems) may selectively refrain from any copying of their material (i.e., without the use of SCPS).

In this case, such provided devices may set (to a high level) a second (copy-protected) bit in their original material. On the other hand, when it is desired to completely stop copying of the material, an additional copy protection position (not related to the SCPS bits) may be designated, such an additional AC bit being also detected by the AC bit detectors 32, 46 which, in response to the detection result, may stop recording or provide analog copy protection, respectively.

On the other hand, the AC bit detector 46 is capable of detecting any of the SCPS bits and thereby enabling the ACP signal generator 50 to copy protect the analog output signal at the terminal 24.

The output signal at the digital video terminal 42 is then used (e.g. to record the output signal using a second recorder of the type shown in figure 1) to inhibit copying of such material by detecting the set AC bit by the AC bit detector 32 of the second recorder.

Thus, the digital video signal recording standard involves copy protection on a bit-by-bit basis using specifically designated bits in the digital video signal stream. These "SCPS" bits and other copy protection bits are provided in one embodiment, for example, in each video field or frame, for copy protection on a field-by-field or frame-by-frame basis.

Thus, the apparatus of fig. 1 is fully analog and digital copy protected. That is, a conventional analog copy protection signal can be detected for various types of known analog copy protection signals at the input side. A digital video copy protection system including a continuous copy restriction is also provided on the input side. On the output side, copy protection is provided for the output analog side of the reproduced digital recorded material. The detailed circuit configuration of the copy protection detectors 32, 46, the SCPS bit detector 54 and the AC bit adder 60 depends on the characteristics of the future digital video recording protocol (format) and can be readily fabricated by those skilled in the art given the knowledge of this format for these circuits. The protocol will inform the manufacturer of the digital video recorder and the supplier of the digital video material program.

In another variant embodiment, the ACP detector 26 does not detect the copy protection signal described in the above-mentioned reference US4,907,093, but directly detects the analog copy protection signal. This may be accomplished, for example, by including an Automatic Gain Control (AGC) circuit for reducing the level (amplitude) of the video signal so that the reproduced material is not viewable.

The analog-to-digital converter 16 will likely need to include an AGC circuit and this circuit can be easily designed to damage the copy protection signal which affects the level of the video signal.

It should also be understood that the apparatus of fig. 1 need not be a tape recorder, but may be a single player, and thus includes only the digital playback tape drive 10 and the circuitry on the right hand side of fig. 1, without the input circuitry on the left hand side. In this case, the output circuit, like the upper right portion and the lower right portion of fig. 1, acts on the copy protection bit present in the pre-recorded digital material reproduced on the tape drive 10. In another type, a compact disc (digital) player replaces the digital playback tape drive 10. Thus, the top right circuitry of the apparatus of fig. 1 is applied to a playback machine for refraining from re-recording copy protected digital video material from the analog output terminal 24.

Another embodiment is for digital or analog video material that is not copy protected in its original form for technical or other reasons and that provides a standard video (e.g., VTSC) signal during playback. One example is the so-called "laser disc" for distributing prerecorded video material by playback on a laser disc recorder. The copy protection schemes in the previously described U.S. Pat. nos. 4,631,603 and 4,914,694 are incompatible with laser discs for technical reasons, since the inclusion of such copy protection schemes in laser discs creates playback problems.

Therefore, there is a need for a copy protection scheme to deter unauthorized recording of signals for playback from a laser disc. This is accomplished by providing an otherwise conventional laser disc player with additional circuitry in accordance with the present invention which includes (1) a copy protection (AC) flag detector (2) an ACP signal generator operatively connected to the copy protection flag detector, whereby video material recorded on the laser disc has a copy protection flag. This copy protection flag is typically a signal having a particular level in a predetermined line of each VB1 of the video material. (analog video, not digital video, is recorded on a laser disc.)

The anti-copy flag (corresponding to the anti-copy bit of fig. 1) is detected by an anti-copy flag detector in the laser disc player, and in response to this detection, the ACP signal generator modifies the analog signal output by the laser disc player in accordance with conventional analog anti-copy processing. This prevents the use of video tape recording consisting of analog output signals played from a laser disc.

Similar modifications can be used in recently developed "WVHS" video tape recorders that record high definition TV signals in the "Wide VHS" video format. WVHS is a video format different from standard (NTSC, PAL or SECAM) video. In this case, the modified WVHS video tape recorder detects the copy protection flag in the pre-recorded material being played back on the WVHS video tape recorder and, in response to this detection, modifies the standard video (e.g., NTSC) signal being played back using conventional analog copy protection processing.

This embodiment is illustrated in fig. 2, which is a block diagram of a player (e.g., a compact disc player) or recorder (e.g., WVHS VCR) suitable for use in accordance with the present invention.

The player includes a conventional player/electrical structure 72, an anti-copy (AC) flag detector 74, and an ACP signal generator 50. Detection of the AC flag by detector 74 from standard (e.g., NTSC) video played back by the machine/electrical configuration 72 results in an "enable" signal being transmitted on line 88 to the ACP signal generator 50 so that the ACP signal on line 88 is mixed with (or modified by) the NTSC video output at terminal 80. The second output signal on line 88 is another type of video signal, such as HDTV (high definition TV) or WVHS, for which conventional copy protection is not applicable, and thus no ACP modification is made to the video on line 88.

The recorder player (e.g., WVHS VCR) also includes an input video terminal 84. If the AC flag is present in the video input at terminal 84 and is still present after recording by the electromechanical structure 72, then this flag is detected by the AC flag detector 74 at playback and as before the ACP signal generator 50 is enabled to copy protect the NTSC video being played back at terminal 80 (the AC flag present at playback depends on the particular format of the input video signal and the characteristics of the electromechanical structure 72). Similarly, playing back pre-recorded video data with an AC flag activates the ACP signal generator 50.

The foregoing description is intended to be illustrative rather than limiting and further modifications will be apparent to those of ordinary skill in the art in light of the foregoing disclosure. It should be appreciated that the apparatus and method described above are readily adaptable to currently available digital video recorders, since currently consumer-type digital video recorders are not available, but only digital video professional systems.

Claims (6)

1. A method of providing a continuous copy protection scheme for a digital video signal comprising a digital video bit stream including continuous copy protection scheme bits, including a continuous copy protection scheme bit reader or detector and a copy protection bit adder, the method comprising:

providing a digital video bit stream to a continuous copy protection scheme bit reader or detector;

outputting a start signal for starting the anti-copy bit adder from the continuous copy protection scheme bit reader or the detector if the continuous copy protection scheme bit is detected;

adding, by the anti-copy bit adder, an anti-copy bit to a predetermined position of the digital video signal in response to the start signal;

reading or detecting an anti-copy bit in the digital video signal to provide a control signal;

adding a digital copy protection signal to the digital video signal in response to the control signal; and

the digital video signal and the digital copy protection signal are converted into an analog video signal containing an analog copy protection signal.

2. A method of providing a continuous copy protection scheme for a digital video signal comprising a digital video bit stream including continuous copy protection scheme bits, including a continuous copy protection scheme bit reader or detector and a copy protection bit adder, the method comprising:

providing a digital video bit stream to a continuous copy protection scheme bit reader or detector;

generating, by a continuous copy protection scheme bit reader or detector, an enable signal for enabling the anti-copy bit adder if the continuous copy protection scheme bit is detected;

adding an anti-copy bit to a predetermined position in the digital video signal in response to the start signal;

detecting an anti-copy bit in the digital video signal;

converting the digital video signal into an analog video signal; and

an analog copy protection signal is added to the analog video signal in response to the detected copy protection bit.

3. A method of providing a continuous copy protection scheme for a digital video signal consisting of a digital video bit stream containing continuous copy protection bits, wherein a continuous copy protection signal reader or detector and a copy protection bit adder are provided, the method comprising:

coupling a digital video bitstream to a continuous copy protection signal reader or detector;

wherein if the continuous copy protection scheme bit is detected, the continuous copy protection signal reader or detector outputs a start signal to start the anti-copy bit adder;

whereby, in response to the continuous copy protection signal reader or detector, a copy protection bit is added to a predetermined position of the digital video signal;

reading or detecting an anti-copy bit in the digital video signal to provide a control signal;

adding a digital copy protection signal to the digital video signal in response to the control signal; and

the digital video signal and the digital copy protection signal are converted into an analog video signal containing an analog copy protection signal.

4. An apparatus for providing a continuous copy protection scheme for a digital video signal composed of a digital video bit stream containing continuous copy protection scheme bits, including a continuous copy protection scheme bit reader or detector and a copy protection bit adder, the apparatus comprising:

means for providing a digital video bit stream to a continuous copy protection scheme bit reader or detector;

means for outputting an enable signal to enable the copy protection bit adder from the continuous copy protection scheme bit reader or detector;

wherein the copy prevention bit is added to a predetermined position of the digital video signal by the copy prevention bit adder in response to the start signal;

second means for reading or detecting an anti-copy bit in the digital video signal to provide a control signal;

means for adding a digital copy protection signal to the digital video signal in response to the control signal; and

means for converting the digital video signal and the digital copy protection signal into an analog video signal comprising an analog copy protection signal.

5. An apparatus for providing a continuous copy protection scheme for a digital video signal composed of a digital video bit stream containing continuous copy protection bits, wherein a continuous copy protection signal reader or detector circuit and a copy protection bit adder circuit are provided, the apparatus comprising:

circuitry for coupling the digital video bit stream to a continuous copy protection signal reader or detector circuit;

wherein if a Sequential Copy Protection Scheme (SCPS) bit is detected, an output of the sequential copy protection signal reader or detector circuit outputs an enable signal;

an anti-copy bit adder circuit for adding an anti-copy bit to a predetermined position of the digital video signal in response to the continuous copy protection signal reader or detector circuit;

a circuit for reading or detecting the copy protection bit in the digital video signal to provide a control signal;

a circuit for adding a digital copy protection signal to the digital video signal in response to a control signal; and

a circuit for converting a digital video signal and a digital copy protection signal into an analog video signal containing an analog copy protection signal.

6. An apparatus for providing a continuous copy protection scheme for a digital video signal formed from a digital video bit stream containing continuous copy protection bits, comprising:

a continuous copy protection signal reader or detector for outputting an enable signal in response to detection of a continuous copy protection bit;

a copy protection bit adder for adding a copy protection bit to a predetermined position of the digital video signal in response to the start signal to provide a continuous copy protection scheme;

a second detector for detecting the copy protection bit;

circuitry for providing an analog video playback signal; and

a copy protection generator for providing a copy protection signal in response to the detected copy protection bit and for modifying the analog video playback signal in response to the copy protection signal.