JPS6052629B2 - Recorded recording medium and its production method - Google Patents

Description

[Detailed Description of the Invention] With the spread of VTRs, it has become a viable business to sell pre-recorded tapes containing movies and the like.

However, by preparing two VTRs, for example,
Copies can be easily made from recorded tapes, that is, dubbing can be performed. Although the act of making such duplicate tapes is prohibited by law, it cannot be regulated if it is done on a small scale, such as in ordinary households.

It is also inconvenient for tape manufacturers. In view of these points, the present invention seeks to provide a recorded tape that cannot be dubbed and a method for producing the same. First, considering general VTRs, there are the following M°C circuits for recording video signals.

In FIG. 1, reference numeral 1 denotes an input terminal, to which a composite video signal St having a horizontal synchronizing pulse Ph and a video signal Sv is supplied as shown in FIG. Circuit 3 and recording/playback switch 1
4 to the rotary head 4 and recorded on the magnetic tape 5.

At this time, the M°C circuit is configured as follows.

That is, the signal St is supplied to the synchronization separation circuit 6 to separate the horizontal synchronization pulse Ph, and this pulse Ph is supplied to the waveform shaping circuit 7, the delay circuit 8, and the phase inversion amplifier 9 to generate the horizontal synchronization pulse as shown in FIG. 2B. A pulse signal Sp having a level Vp approximately equal to the white peak level of the video signal Sv is formed at a position corresponding to the back porch of the synchronizing pulse Ph. This signal Sp and the signal St from the amplifier 2 are added in an adder circuit 10 to form an added signal Ba as shown in FIG.
The voltage value from the tip of h to the tip of signal Sp (Vp+Vh
) [Vh is the level of the pulse Ph] is extracted, and this detected signal is supplied to the amplifier 2 as a control signal for its gain. Therefore, when the level of the signal St changes, the level Vh of the pulse Ph also changes, so the voltage value (Vp + Vh) taken out from the detection circuit 11 changes, and the gain of the amplifier 2 is adjusted so that this value becomes a constant value. By being controlled, the level of the signal Sv supplied to the recording circuit 3 is controlled to a constant level.

Therefore, the supplied signal St is always recorded on the tape 5 at a constant level, and when the white peak of the video signal Sv becomes excessively input, especially in a camera input, the level of the video signal Sv changes. Since it exceeds the level of the pulse signal Sp, the voltage value extracted by the detection circuit 11 changes rapidly in accordance with the level ratio of the horizontal synchronizing pulse Ph and the video signal Sv, and faster gain control is possible. It has been done and is valid. Note that during playback, the composite video signal St taken out by the head 4 is transferred to the switch 14 and the playback circuit 1.
2 to the output terminal 13.

The present invention focuses on the fact that a VTR is equipped with such an AGC circuit, and although a recorded tape can be played back, when a duplicate tape is created by dubbing from this tape, this duplicate tape This is an attempt to prevent dubbing by preventing a normal playback screen from being obtained even when the video is played back.

An example of the present invention will be described below. FIG. 3 shows an apparatus for producing a recorded tape (or its master tape). In the figure, 21 is a composite video signal St (second
Figure A) is the input terminal that is supplied.

This signal St is supplied to the adder circuit 23 through the amplifier 22. The signal St is also supplied to the synchronization separation circuit 24 to separate the horizontal synchronization pulse Ph, this pulse Ph is supplied to the waveform shaping circuit 25 for waveform shaping, and this shaped signal is supplied to the delay circuit 26 for horizontal synchronization. Synchronous pulse Ph
This delayed signal is supplied to the modulation circuit 27 as a carrier wave signal. Further, in the oscillation circuit 32, a rectangular wave signal Sm is generated, for example, the period of one field is "1" every four fields, and the period of the remaining three fields is "0", and this signal Sm is sent to the modulation circuit 27 for modulation. A modulated pulse signal Sp (FIG. 2B) with a level p approximately equal to the white peak level of the video signal Sv is formed only during one field period when the signal Sm is supplied as an input and is at "1". This signal Sp is supplied to the adder circuit 23.

Therefore, from this adder circuit 23, every 4 fields are
unit, the composite video signal St is extracted during the 3-field period in which the signal Sm is "0", and the added signal Sa as shown in FIG. 2C is extracted during the remaining 1-field period.Then, this signal Sa and St are sequentially supplied to the rotary head 29 through the recording circuit 28 and recorded on the magnetic tape 30.

Each servo system for controlling the rotational phase of the rotary head 29 and the transport speed of the tape 30 is constructed in the same manner as in the conventional system. In this way, a recorded tape (or master tape) 30 is produced, but in this case, the recorded signal is white on the back pouch of the horizontal synchronizing pulse Ph of the composite video signal St for the period of one field every four fields. This is the sum of pulse signals Sp having a magnitude corresponding to the peak level. Therefore, when this recorded tape 30 is played back by the VTR shown in FIG.
A signal Sa is reproduced during the field, and this signal St
and Sa are taken out to the output terminal 13 through the reproduction circuit 12 (FIG. 4A).

When the signals St and Sa are supplied to a television receiver for monitoring, the synchronization pulses Ph and P of the signal Sa are
Since y and the video signal Sv are the same as the normal composite video signal St, a normal playback screen can always be obtained.

On the other hand, if you prepare another TR and perform recording (duping) by supplying the reproduced signals St and Sa to the input terminal 1 of that VTR, the period of one field out of every four fields is The signal Sa from the amplifier 2 is sent to the adder circuit 10.
is supplied to

On the other hand, since the amplifier 9 always supplies the pulse signal Sp, the adder circuit 10 outputs the signal as shown in FIG. 2D during this period.
A pulse signal of the same magnitude is further added to the pulse signal Sp to obtain a signal Sb with a pulse signal Sp'' of twice the magnitude.Then, this signal Sb is supplied to the detection circuit 11 to generate a pulse signal. Signal Sp'' from the tip of Ph
The voltage value up to the tip of is taken out, and the gain of the amplifier 2 is controlled so that this voltage value becomes the normal magnitude (Vp+Vh). Therefore, the gain of the amplifier 2 is significantly lowered during the period when this signal Sa is supplied, and the video signal Sv
The level will be suppressed to the normal level of 112.

This suppression is performed every 4 fields, but since the recovery time of the AGC circuit is usually set to about 1110 seconds, once suppression is performed, the subsequent 3 fields are gradually processed as shown in Figure 4B. Its level will start to rise. Then, when the level returns to almost the normal level, the signal Sa is supplied again and the level of the video signal Sv is suppressed. Therefore, when the duplicate tape 5 made in this way is played back and supplied to a monitor receiver, the reproduced image changes drastically in contrast, brightness, etc. at a period of 4 fields (seconds), and flickers. This results in an extremely unsightly screen that is of no practical use.

Thus, according to the present invention, when the recorded tape 30 is played back and the playback signal is supplied to a monitor receiver, a normal playback screen can be obtained, but this signal is supplied to another VTR to reproduce the duplicate tape. In this case, even if this duplicate tape is played back, the playback screen will not be of any practical use, and only a useless duplicate tape will be created, so it is possible to prevent dubbing. In addition, in the above, AGC
Although the circuit shown in Figure 1 was explained, the general N
A similar effect can be obtained with a °C circuit.

Furthermore, in the above example, the interval at which the pulse signal Sp is inserted is every four fields, but this may be set to an interval corresponding to the recovery time of the N°C circuit in the recording side VTR used when making a duplicate tape.

Further, the modulation of the pulse signal Sp is changed to the signal St from the terminal 21.
It may be synchronized with the vertical synchronization pulse of Furthermore, the same effect can be obtained not only by inserting the signal Sp intermittently as described above, but also by inserting a pulse signal Sp whose level changes in an analog manner throughout. may also be changed periodically,
When changing the position, width, etc. of the pulse signal Sp, the position is set such that it periodically overlaps or does not overlap with the N°C pulse Sp. Further, the pulse signal Sp may be inserted at any position as long as it causes the AGC circuit to malfunction. For example, as shown in FIG. 5A, the synchronizing pulse Ph
A pulse signal Sp having the same polarity as , may be inserted so that the level of the peak value of the pulse Ph changes, or may be inserted into the pulse Ph as shown in FIG. 5B. Incidentally, by attaching the above-mentioned device to a general TR, it is possible to prevent the user from dubbing what has been recorded from broadcasts, etc.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a general VTR, FIGS. 2 and 4 are waveform diagrams for explaining the present invention, and FIG. 3 is a system diagram of an example of a device for producing a recorded tape according to the present invention. FIG. 5 is a waveform diagram of another example. 30 is a recorded tape.

Claims (1)

[Scope of Claims] 1. A recorded recording medium in which a pulse signal whose level, position, width, or polarity changes at the cycle of a plurality of fields is added to the horizontal retrace period of a composite video signal, and this added signal is recorded. 2. Separate the horizontal synchronizing pulse of the composite video signal, and, based on this horizontal synchronizing pulse, determine the level, position, width, or polarity of the horizontal synchronizing pulse at a position corresponding to the horizontal retrace period of the composite video signal with a period of multiple fields. A method for producing a recorded recording medium, in which a changing pulse signal is formed, and this pulse signal is added to the composite video signal for recording.