GB2055501A - Video tape recording apparatus - Google Patents
Video tape recording apparatus Download PDFInfo
- Publication number
- GB2055501A GB2055501A GB7927090A GB7927090A GB2055501A GB 2055501 A GB2055501 A GB 2055501A GB 7927090 A GB7927090 A GB 7927090A GB 7927090 A GB7927090 A GB 7927090A GB 2055501 A GB2055501 A GB 2055501A
- Authority
- GB
- United Kingdom
- Prior art keywords
- signal
- pulses
- vertical
- vertical synchronising
- tape
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/00086—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B27/00—Editing; Indexing; Addressing; Timing or synchronising; Monitoring; Measuring tape travel
- G11B27/10—Indexing; Addressing; Timing or synchronising; Measuring tape travel
- G11B27/19—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier
- G11B27/28—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier by using information signals recorded by the same method as the main recording
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/48—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
- G11B5/58—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
- G11B5/584—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following on tapes
- G11B5/588—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following on tapes by controlling the position of the rotating heads
-
- 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
Landscapes
- Engineering & Computer Science (AREA)
- Signal Processing (AREA)
- Computer Security & Cryptography (AREA)
- Multimedia (AREA)
- Television Signal Processing For Recording (AREA)
Abstract
A video tape recording apparatus is arranged to replace every (or every n<th>) vertical synchronising signal of a video signal to be recorded, prior to its reaching a recording head of the apparatus, with a modified vertical synchronising signal comprising an initial long pulse (S1) and a series of short pulses (S2). The voltage pulse resulting from integration of the modified vertical synchronising signal has a lower energy content than that resulting from integration of a standard vertical synchronising signal, but has a fast rise time due to 'lumping' of the energy at the start. The voltage pulse peak amplitude exceeds the trigger threshold voltage VTV of circuitry of most TV monitors, whereby a tape recorded on the apparatus can be satisfactorily played back. However, the voltage pulse peak amplitude does not attain the trigger threshold VVTR of a typical video tape recorder (VTR), whereby a tape produced on the apparatus cannot readily be satisfactorily copied on a VTR. <IMAGE>
Description
SPECIFICATION
Video tape recording apparatus
This invention relates to video tape recording apparatus.
Conventional video tape recording apparatus reproduces on the tape the synchronising information present in the video signal recorded.
This enables the tape to be readily copied, possibly unlawfully, even by a non-professional using a domestic video tape recorder.
According to the present invention there is provided video tape recording apparatus comprising a recording head for recording a video signal on a tape, head servo means for controlling movement of the head with respect to the tape, vertical pulse generator means operative to generate vertical pulses in synchronism with vertical synchronising signals of the video signal to be recorded, said means being connected to supply the pulses to the servo means to lock the servo means to the video signal to cause the video signal to be properly recorded, and means operative to replace at least some of the vertical synchronising signals, prior to their reaching the head, with modified vertical synchronising signals each comprising an initial pulse of relatively long duration followed by a plurality of pulses of relatively short duration.
As is explained in more detail below, the modified vertical synchronising signal can enable an average TV monitor satisfactorily to lock to the video signal on the tape when the tape is replayed, yet can prevent another video tape recorder (VTR) locking to the video signal if an attempt is made to copy the tape on the other VTR, whereby satisfactory copying is difficult and expensive. This effect is due to the fact that the modified vertical synchronising signal, when integrated, is of such a nature that it will trigger the generation of a field pulse in the average TV monitor but not in the average VTR.
The durations of the initial long pulse and the following short pulses may be chosen on an empirical and/or theoretical basis to attain the desired selective triggering effect, in accordance with the teachings of the following disclosure. The mark/space ratio of the plurality of relatively short pulses may be less than unity, though this is not essential.
The initial pulse may commence prior to the start of the vertical synchronising signal replaced by the modified signal containing the initial pulse.
Means may be provided to enable the position in time of the leading edge of the initial pulse to be varied.
The invention also provides a video tape bearing a recording made by apparatus as set forth above.
The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which:
Figure 1 shows the vertical interval pulse train of a television (video) signal;
Figure 2 is a schematic representation of a conventional video tape recorder when recording from a video source;
Figure 3A shows a part of the pulse train of
Figure 1 on an enlarged scale;
Figure 3B shows the energy content of the part of the pulse train shown in Figure 3A;
Figure 4A shows a vertical synchronising signal portion of the pulse train shown in Figure 3A;
Figure 4B shows a voltage pulse obtained by integrating the vertical synchronising signal shown in Figure 4A;
Figure 4C shows a modified vertical synchronising signal substituted for the vertical synchronising signal of Figure 4A in apparatus embodying the invention;;
Figure 4D shows a voltage pulse obtained by integrating the modified vertical synchronising signal of Figure 4C; and
Figure 5 is a schematic representation of the apparatus embodying the invention.
Figure 1 shows a television or video waveform, more particularly the so-called vertical interval a thereof which provides for vertical (or field) synchronisation and which occurs every field (i.e.
twice per frame). The vertical interval a comprises a train of pulses and has, in the PAL system, a duration of 25 lines, the duration of one line being shown at b. The vertical interval a includes a group c of negative-going vertical synchronising pulses, which group is referred to herein as 'the vertical synchronising signal', from which a vertical or field pulse is derived in a TV monitor and in a video tape recorder as explained hereinbelow. In the
PAL system, the vertical synchronising signal c has a duration of 2.5 lines.
Figure 2 shows a conventional video tape recorder (VTR) 10 recording in conventional manner a video signal from a video source 12 supplied with synchronising signals from a sync pulse generator 14. (Alternatively, as appropriate, the generator 14 could be omitted and synchronising information from the video signal from the source 10 used instead). The VTR 10 may be of the cassette or open reel type. The video signal is fed, via video record circuits 16, to a magnetic recording head 18. The head 18 is mounted on a head wheel or drum (not shown) which is so moved with respect to a video tape (not shown) that the video signal is recorded thereon in the form of a plurality of adjacent tracks extending along and across the tape and each storing, for example, one frame of the signal.A control track is also recorded on the tape to synchronise the tape, in known manner, during subsequent playback.
To ensure that the recording is properly made, i.e. to ensure that a track change is made at the correct point in the video signal so that the tape, when played back is intelligible, a head servo 20 which drives the head 18 is locked to vertical synchronising pulses synchronous with and derived from the vertical synchronising signals of the video signal from the source 12. The vertical synchronising pulses may be frame or field synchronising pulses (i.e. they may be the frame or field frequency) in accordance with the construction of the particular VTR 10, though it will be assumed in the following that field pulses are employed.
The derivation of the vertical pulses is performed as follows. A vertical sync separator means 22 is connected to receive the video signal from the source 12. In known manner, the sync separator means 22 comprises a sync separator to extract the vertical synchronising signals from the video signal, an integrator to integrate the pulse of each such signal to form a longer voltage pulse, and a voltage dependent circuit (e.g. a monostable circuit) triggered to produce a field synchronising pulse when the integrator output pulse amplitude exceeds a threshold level. (If the head servo 20 locks to frame pulses rather than to field pulses, the sync separator means 22 may also comprise a circuit to divide by two the field synchronising pulses to produce vertical synchronising pulses at the frame frequency.) The vertical pulses are fed to the head servo 20.Also fed to the head servo 20 are pulses from a pickup or pickups 24 operative to supply pulses at predetermined increments of rotation of the head wheel. The head servo 20 is operative to drive the head wheel, as shown schematically at 26, in such a manner that the pulses from the pickup(s) 24 stay locked to those from the sync separator means 22, whereby the movement of the head 1 8 is maintained synchronised with the video signal.
In the VTR 10 of Figure 2, the vertical synchronising signals are recorded on the tape produced by the VTR. Consequentially, the tape could readily be properly copied, possibly unlawfully, even by a non-professional using a domestic VTR. An embodiment of the invention described hereinbelow enables the production of a tape which is much ignore difficult to copy properly, and in particular which cannot readily be copied on an unmodified domestic VTR and/or by the amateur.
Referring to Figure 1, and also to Figure 3A which reproduces part of Figure 1 on an enlarged scale, it can be seen that the vertical interval pulse train, viewed with respect to a reference level L, comprises negative-going relatively broad pulses
S (the vertical synchronising signal c) which are both preceded and followed by trains of negativegoing equalising pulses E. The approximate energy content of the train of pulses is shown in Figure 3B. In a VTR, and also in a video monitor (e.g. a domestic television receiver), the energy content of the pulse train is realised by integrating the pulse train by means of an integrator (as mentioned above for the VTR 10) comprising a network having a sufficiently long time constant.
This enables the vertical synchronising signal pulses to be discriminated from the line synchronising pulses of the vertical interval to provide the field synchronising pulses. The integration operation effectively discriminates between the amount of energy contained in the different pulses, the energy being proportional to the area occupied by the pulses. The energy contained in the vertical synchronising interval c is proportional to:
(a) the peak amplitude of its constituent pulses
S;
(b) its overall duration; and
(c) the mark/space ratio of the constituent pulses S.
In the embodiment of the invention to be described below, parameters (a) and (b) are substantially unmodified and comply with normal broadcast practice, but parameter (c) is varied so as to influence the total energy content. The synchronising pulse separator that detects the equalising pulses E requires the negative-going edge of each pulse to be in a constant (timerelated) position, but it is not possible to vary the duration of the pulses (within limits) without adversely affecting synchronising pulse circuits, whereby the energy of the vertical synchronising signal can be varied without undue adverse effects on other circuits.
Because of typical design parameters involved in TV monitors and VCRs, the voltage pulses derived by integrating the vertical synchronising signal pulses are used as voltage triggers to lock an oscillator, in the case of a television monitor, or the head wheel or drum servo in the case of a VTR.
Television monitors are designed to provide good handling of poor quality or low energy signals, and as a result are 'signal-tolerant' in that they are capable of responding satisfactorily to a video signal with a lower than standard amount of energy in the vertical synchronising signal.
However, this is not the case in a VTR.
Figure 4A again shows the vertical synchronising interval (c) of the waveform of
Figure 1 and Figure 4B shows a typical voltage pulse obtained by integrating the pulses S thereof.
The voltage pulse of Figure 4B, as mentioned above, is used both in a TV monitor and in a VTR to trigger a voltage-dependent circuit (e.g. a monostable circuit) to produce a field pulse. As can be seen, there is a time delay between the leading edge (t1) of the vertical synchronising signal and the trigger point (t2), i.e. the point in time where the pulse is of amplitude equal to the trigger threshold voltage (VTV for the TV monitor and VVTR for the VTR) of the voltage-dependent circuit to trigger the circuit providing the field pulse. In the embodiment of the present invention described below with reference to Figures 4C, 4D and 5 the energy content of the vertical synchronising signal is modified such that the peak value attained by the integrated signal is sufficient to trigger the signal-tolerant circuitry in most if not all TV monitors, but is not sufficient to trigger the relatively intolerant circuit employed in
VTRs.
The apparatus embodying the invention shown in Figure 5 can be of substantially the same construction as the known apparatus shown in
Figure 2, except for the interposition between the video source 12 and the VTR 10 of a vertical synchronising signal modifying circuit arrangement 30, and the sync separator 22 being connected directly to the sync pulse generator 14.
The arrangement 30 essentially comprises a pulse generator 32, a gate 34 connected to receive the video signal (including synchronising signals) from the video source 12 on one input and pulses from the pulse generator 32 on another input, and a timer 36 connected to receive the synchronising information from the video signal and connected to a control input of the gate 34 to switch the gate to pass the signal at one or the other of its inputs to the VTR 10. More specifically, the timer is operative to sense the presence of the vertical synchronising signal C from the video source 12 and, instead of transmitting it to the VTR 10, to instead supply to the VTR 10, from the pulse generator 32, the series of pulses shown in Figure 4C.In other words, the standard vertical synchronising signal comprising a plurality of like pulses S is replaced by a series of pulses comprising an initial, relatively broad pulse S, followed by a succession of relatively narrow pulses S2, whereby the signal recorded on the tape is the same as in the set-up of Figure 2, except that the vertical synchronising signals are modified. The voltage pulse resulting from integration of the pulse series of Figure 4C, either in a TV monitor or in a VTR, is shown in Figure 4D.
As can be seen, the pulse from the integrator has a lower energy content than the standard pulse, but has a fast rise time (t1 - t2,) due to 'lumping' of the energy of the vertical synchronising signal at the start. As can be seen from Figure 4D, the integrator output pulse peak amplitude exceeds the trigger threshold VTV of the 'signal-tolerant' voltage dependent circuit of most TV monitors, whereby, when a tape produced on the VTR 10 is replayed on a VTR, the VTR locking to the control track in conventional manner, the monitor has no difficulty in remaining synchronised to the signal recorded on the tape.However, the peak amplitude of the integrator output pulse does not attain the trigger threshold VVTR. Consequently, if an attempt is made to copy the tape by feeding the signal recorded thereon to another VTR, the 'intolerant' sync. separator circuitry of the other
VTR will fail to develop field pulses so that its head will not lock in a stable manner to the video signal and a satisfactory copy cannot be made.
The arrangement 30 may be operative to modify each successive vertical synchronising signal as set forth. However, it may be found advantageous in some circumstances only to modify each nth successive such signal, where n is an integer which may typically range between 3 and 200. This can readily be accomplished by designing the timer 36 to count vertical synchronising signals and only to cause the gate 36 to be connected to the pulse generator 32 at every nth such signal. In this case, if an attempt to copy is made, the VTR on which the copy is being made may lock to the video signal during the periods between modification of the vertical synchronising signals.However, since these periods are short, and since a monitor fed with the tape copy will temporarily lose vertical synchronisation at the end of each such period, the picture quality will be unacceptable, i.e. a satisfactory copy will not have been made.
If the modified vertical synchronising signal did not have a fast rise time (t1 - t2,), a problem could arise, in the case where only every nth vertical synchronising signal is modified, because there might be timing variations between the start of vertical scanning on different fields, causing vertical jitter of the picture generated on playback of the tape. However, due to the fast rise time, this problem should not normally occur.
As illustrated in Figure 4C, the modified vertical synchronising signal comprises the initial broad pulse S, and a subsequent series of narrow pulses S2, the mark/space ratio of the pulses S2 being less than unity. Also as illustrated, the broad pulse
S, may commence prior to the start of the vertical synchronising signal c. Means may be provided enabling the position of the leading edge of the pulse S, to be varied, so enabling the correction of any abnormal timing errors between the vertical synchronising signal and the integrated pulse shown in Figure 4D by advancing the leading edge of the pulse S,.
In summary, the apparatus of Figure 5 enables the recording of a video tape which is the same as that produced on a conventional VTR, except that at least some of the vertical synchronising signals are replaced by modified vertical synchronising signals as shown in Figure 4C. The recording may subsequently be replayed on a conventional VTR and will satisfactorily lock a normal TV monitor.
However, the tape may not be satisfactorily copied (i.e. re-recorded on another tape) without the trouble and expense of re-constituting the normal vertical synchronising signal. The expense and complexity of such reconstitution should preclude its use by the majority of persons likely to engage in the illicit re-copying of copyright material.
Claims (8)
1. Video tape recording apparatus comprising a recording head for recording a video signal on a tape, head servo means for controlling movement of the head with respect to the tape, vertical pulse generator means operative to generate vertical pulses in synchronism with vertical synchronising signals of the video signal to be recorded, said means being connected to supply the pulses to the servo means to lock the servo means to the video signal to cause the video signal to be properly recorded, and means operative to replace at least some of the vertical synchronising signals, prior to their reaching the head, with modified vertical synchronising signals each comprising an initial pulse of relatively long duration followed by a plurality of pulses of relatively short duration.
2. Apparatus according to claim 1, wherein the duration of the initial long pulse can be varied.
3. Apparatus according to claim 1 or claim 2.
wherein the durations of the plurality of pulses of relatively short duration can be varied.
4. Apparatus according to claim 1, claim 2 or claim 3, wherein the mark/space ratio of the plurality of relatively short pulses is less than unity.
5. Apparatus according to any one of the preceding claims, wherein, in use, the initial pulse commences prior to the start of the vertical synchronising signal replaced by the.modified signal containing the initial pulse.
6. Apparatus according to any one of the preceding claims, including means to enable the position in time of the leading edge of the initial pulse to be varied.
7. Apparatus according to any one of the preceding claims, arranged to replace every nth vertical synchronising signal with a modified vertical synchronising signal, n being an integer from 3 to 200.
8. Video tape recording apparatus substantially as herein described with reference to Figures 4C, 4D and 5 of the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7927090A GB2055501A (en) | 1979-08-03 | 1979-08-03 | Video tape recording apparatus |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7927090A GB2055501A (en) | 1979-08-03 | 1979-08-03 | Video tape recording apparatus |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB2055501A true GB2055501A (en) | 1981-03-04 |
Family
ID=10506971
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB7927090A Withdrawn GB2055501A (en) | 1979-08-03 | 1979-08-03 | Video tape recording apparatus |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2055501A (en) |
Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0084241A2 (en) * | 1982-01-18 | 1983-07-27 | Shinano Kikaku Kabushiki Kaisha | Signal processing device and method for video tape recording |
| FR2534433A1 (en) * | 1982-10-08 | 1984-04-13 | Thomson Csf | METHOD FOR PROTECTING A SEQUENCE OF VIDEO IMAGES AGAINST FRAUDULENT USE AND DEVICES FOR IMPLEMENTING SAID METHOD |
| US4571642A (en) * | 1981-08-24 | 1986-02-18 | Hofstein Steven R | Method of and apparatus for modifying a video signal to prevent the unauthorized recording and reproduction thereof |
| EP0172439A2 (en) * | 1984-08-13 | 1986-02-26 | Verbatim Corporation | Copy protected disk |
| WO1986005057A1 (en) * | 1985-02-22 | 1986-08-28 | Arie Marinus Wijnen | A method and an apparatus for protecting video signals |
| US4695901A (en) * | 1986-03-04 | 1987-09-22 | Macrovision | Method and apparatus for removing pseudo-sync and/or agc pulses from a video signal |
| WO1988002588A1 (en) * | 1986-09-24 | 1988-04-07 | Conny Togeretz | Method of preventing unauthorized reproduction of the content of video cassette tapes and apparatus for executing the method |
| EP0301504A2 (en) * | 1987-07-29 | 1989-02-01 | Scitec Corporation | Method of copy protecting a pre-recorded videotape |
| WO1991016791A1 (en) * | 1990-04-20 | 1991-10-31 | Copyguard Enterprises S.A. | A method and an apparatus for preventing unauthorized copying of video signals on tape |
| US5155767A (en) * | 1991-11-12 | 1992-10-13 | Noller Robert R | Method and apparatus for manufacturing pre-recorded videotape programs |
| US5418853A (en) * | 1992-07-24 | 1995-05-23 | Sony Corporation | Apparatus and method for preventing unauthorized copying of video signals |
-
1979
- 1979-08-03 GB GB7927090A patent/GB2055501A/en not_active Withdrawn
Cited By (18)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4571642A (en) * | 1981-08-24 | 1986-02-18 | Hofstein Steven R | Method of and apparatus for modifying a video signal to prevent the unauthorized recording and reproduction thereof |
| EP0084241A2 (en) * | 1982-01-18 | 1983-07-27 | Shinano Kikaku Kabushiki Kaisha | Signal processing device and method for video tape recording |
| EP0084241A3 (en) * | 1982-01-18 | 1984-10-03 | Shinano Kikaku Kabushiki Kaisha | Signal processing device and method for video tape recording |
| FR2534433A1 (en) * | 1982-10-08 | 1984-04-13 | Thomson Csf | METHOD FOR PROTECTING A SEQUENCE OF VIDEO IMAGES AGAINST FRAUDULENT USE AND DEVICES FOR IMPLEMENTING SAID METHOD |
| EP0107567A1 (en) * | 1982-10-08 | 1984-05-02 | Thomson-Csf | Method of protecting a video picture sequence against fraudulent use, and devices for carrying out this method |
| EP0172439A2 (en) * | 1984-08-13 | 1986-02-26 | Verbatim Corporation | Copy protected disk |
| EP0172439A3 (en) * | 1984-08-13 | 1987-02-04 | Verbatim Corporation | Copy protected disk |
| WO1986005057A1 (en) * | 1985-02-22 | 1986-08-28 | Arie Marinus Wijnen | A method and an apparatus for protecting video signals |
| US4695901A (en) * | 1986-03-04 | 1987-09-22 | Macrovision | Method and apparatus for removing pseudo-sync and/or agc pulses from a video signal |
| WO1988002588A1 (en) * | 1986-09-24 | 1988-04-07 | Conny Togeretz | Method of preventing unauthorized reproduction of the content of video cassette tapes and apparatus for executing the method |
| EP0301504A2 (en) * | 1987-07-29 | 1989-02-01 | Scitec Corporation | Method of copy protecting a pre-recorded videotape |
| EP0301504A3 (en) * | 1987-07-29 | 1990-11-22 | Scitec Corporation | Method of copy protecting a pre-recorded videotape |
| US5179452A (en) * | 1987-07-29 | 1993-01-12 | Scitec Corporation | Method for producing copy protected recorded videotape having uncopyable vertical synchronizing signal partition |
| WO1991016791A1 (en) * | 1990-04-20 | 1991-10-31 | Copyguard Enterprises S.A. | A method and an apparatus for preventing unauthorized copying of video signals on tape |
| US5481608A (en) * | 1990-04-20 | 1996-01-02 | Copyguard Enterprises | Method and an apparatus for preventing unauthorized copying of video signals on tape |
| US5155767A (en) * | 1991-11-12 | 1992-10-13 | Noller Robert R | Method and apparatus for manufacturing pre-recorded videotape programs |
| US5418853A (en) * | 1992-07-24 | 1995-05-23 | Sony Corporation | Apparatus and method for preventing unauthorized copying of video signals |
| USRE36763E (en) * | 1992-07-24 | 2000-07-04 | Sony Corporation | Apparatus and method for preventing unauthorized copying of video signals |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |