JPH0237749B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for recording and reproducing television signals by scrambled broadcasting.

In recent years, a scrambled broadcasting system has been proposed, in which a specific program is scrambled and transmitted by a broadcasting station, and only viewers who have a contract with the broadcasting station and have a decoder can view this program. Small-scale experimental broadcasts are being conducted. In scrambled broadcasting, a broadcast station transmits a scrambled signal by changing the level of a television signal of a specific program at an arbitrary period of time or by changing the order of the signals. Therefore, even if a normal television receiver receives a scrambled broadcast television signal, it will not be possible to view the correct image or sound. Only viewers who have a contract with the broadcasting station can use a decoder to restore (descramble) the scrambled signal and view the original images and audio of the program.

The present invention provides a system device suitable for once recording and reproducing such scrambled broadcast television signals, and embodiments of the present invention will be described below with reference to the drawings.

This embodiment is designed to satisfy the following conditions.

(1) It is not possible to simultaneously descramble a scrambled broadcast program while receiving it. In other words, it is not possible to view the correct program in real time.

(2) Once the scrambled broadcast program is
You cannot watch it unless you record it on a VTR.

(3) A tape containing a scrambled broadcast program cannot be viewed correctly unless it is played back on a VTR with a decoder.

(4) VTR can be used in any format.

(5) When adding a decoder, changes to existing VTRs should be kept to a minimum.

(6) Scrambled broadcasting is broadcast using free time during normal broadcasting hours, such as late at night.

1 and 2 show an example of the connection relationship between the VTR 1, the receiver 2, and the receiver 3, and corresponding parts are given the same reference numerals.

In FIG. 1, a conventionally known helical scan type VTR is used as the VTR 1. This VTR 1 includes a tuner 4, a recording and reproducing device 5 including a mechanism and circuit system for recording and reproducing, and a modulator 6 for converting reproduced video signals and audio signals of normal broadcasting into vacant channel frequencies.
etc. are built-in. This modulated signal is applied from the output terminal 7 to the antenna terminal of the receiver 3. On the other hand, the scrambled video signal and audio signal from the recording/reproducing device 5 are applied to the decoder 2 from the output terminal 8, where they are descrambled and become regular signals. This signal passes through the VTR again from the input terminal 9 and is applied to the line-out terminal of the receiver 3 from the line-out terminal 10.

FIG. 2 shows a case where the decoder 2 has a built-in modulator 11, and the descrambled signal is sent to the modulator 1.
1 converts it to an empty channel frequency and applies it to the antenna terminal of the receiver 3. If the descrambled signal is not modulated, this signal is applied to the line-in terminal.

FIG. 3 shows the contents of signals sent out when a certain program is sent out in scrambled broadcasting.

In the audio channel, first, a start signal _S1 indicating that the program is a scrambled broadcast program is added, and then a key discrimination signal _S2 for determining the type of key signal _S5 , which will be described later, is added. Then the scrambled audio signal _S3 of the program is sent out. When the program is finished, a write start signal _S4 is applied to write the key signal _S5 to the memory, and then a key signal _S5 is applied to descramble the scrambled signal _S3 .
Finally, a write stop signal _S6 is applied. In the video channel, after a scrambled program video signal _S7 corresponding to the signal _S3 is added, a vertical synchronization signal VD and a horizontal synchronization signal HD are added to portions corresponding to the signals _S4 to _S6 .

Signals other than programs in the audio channel
S ₁ , S ₂ , S ₃ , S ₄ , S ₅ , and S ₆ are configured as 32-bit binary code signals using the NRZ modulation method, for example. This binary code signal is FSK modulated and superimposed on the television signal. In this case, the binary code "1" is, for example, 1000Hz, and "0" is, for example,
Modulated to 600Hz.

When performing scrambled broadcasting late at night, the VTR 1, decoder 2, and receiver 3 may be operated by detecting the start signal _S1 .

The key signal _S5 is determined as follows.

For example, consider a case where a signal of a certain program is scrambled by changing its level in units of one field. In this case, for example, the signal level of an arbitrary field period in an arbitrary predetermined period of the video signal is lowered by a predetermined amount, and this is repeated every predetermined period.
For example, if the above predetermined period is 5 fields, the first and third fields of the first to fifth fields in this period are
If the level of the field is lowered, descrambling can be performed on the receiving side by increasing the gain of the amplifiers of the first and third fields every five fields. If the key used to increase this gain is "1", the key signal can be represented by a code pattern of "01100". Note that the audio signal is also scrambled and descrambled in the same manner.

In this embodiment, after the recording of the program is completed on the VTR 1, the key signal _S5 is written into the memory built into the decoder 2, and during playback, the key signal _S5 is constantly read out and compared with the playback signal to perform descrambling. This is how it was done. The code of the key signal _S5 is changed for each program, or for each hour, day, week, or month, so that its contents are not known to anyone other than the subscriber. Therefore, if many programs are recorded, many types of key signals will be written to the memory. Therefore, in order to determine which key code should be used to descramble a desired program during playback, a key discrimination signal _S2 is added prior to the program.

Furthermore, in this embodiment, the key signal _S5 is added at the end of the program. This makes it impossible to view scrambled broadcasts in real time, and the correct program cannot be viewed unless it is recorded on tape using VTR1. Note that if the key signal _S5 is not recorded on the tape, even if a copy tape is made, descrambling is impossible because there is no key. Even if a key signal is recorded, descrambling is impossible unless there is a decoder. Note that horizontal and vertical synchronizing signals HD and VD are added to obtain a clock when writing a key signal.

Next, an embodiment of the decoder 2 will be described with reference to FIG.

The decoder 2 includes an audio signal input terminal 15, a video signal input terminal 16, an audio signal output terminal 17, a video signal output terminal 18, a key signal demodulation circuit 19, a synchronous separation circuit 20, a timing circuit 21, a code discrimination circuit 22, and a memory 23. , an audio signal descrambling circuit 24, a video signal descrambling circuit 25, switches 26, 27, 28, etc. as shown in the figure.

During recording, switches 26 and 28 are opened and switch 27 is closed. Input terminal 15 has the previous stage
Signals S ₁ to _{S 6} are sequentially applied from the VTR 1, and signals S ₇ , VD, and HD are applied to the input terminal 16.
At this time, the VTR is set to recording E-E mode.
A monitor signal is applied to input terminals 15 and 16.

When the start signal _S1 shown in FIG. 3 is first detected by the code discrimination circuit 22 from the signal applied to the input terminal 15, each circuit is operated based on this detection.
Next, when the key discrimination signal S ₂ is detected and the type of the key signal S ₅ of the program is discriminated, the discrimination signal S ₈ is written into the memory 23. The synchronization separation circuit 20 extracts the signals VD and HD from the scrambled video signal applied to the input terminal 16 and drives the timing circuit 21. When the program ends, the write start signal _S4 is detected and the memory 23 enters the write mode of the key signal _S5 . Next, the demodulation circuit 19 demodulates the FSK-modulated key signal _S5 to form a binary code key signal.
This key signal is synchronized with the clock through the timing circuit 21 and written into the memory 23 in correspondence with the discrimination signal _S8 . During this time, signals VD and HD are applied from the video channel to obtain the write clock. Incidentally, when the write start signal _S4 is detected by the code discrimination circuit 22, this detection signal is applied to the VTR as shown by the dotted line in the figure, and the operation of the recording circuit is stopped, so that the key signal _S5 is not recorded on the tape. You can do it like this. When writing of the key signal _S5 is completed, a write stop signal _S6 is detected and the write operation is stopped. As described above, the scrambled video signal, audio signal, and other signals (S ₁ , S ₂ , S ₄ to S ₆ , etc.) are recorded on the tape, and the key signal and the type of key signal of the program are stored in the memory 23. is written. The above-mentioned operation is performed every time a scrambled broadcast program is recorded, and a key signal and a key discrimination signal for each program are written in the memory 23, respectively.

Next, during playback, VTR 1 goes into playback mode, switches 26 and 28 are closed, and switch 2 is closed.
7 will be held. A signal obtained by demodulating a signal played back from an audio track of a desired program recorded on a tape is applied to the input terminal 15, and a signal obtained by demodulating a signal played back from a video track of that program is applied to an input terminal 16. It will be done.
First, when the reproduced key discrimination signal _S2 is detected by the code discrimination circuit 22, the corresponding key signal written in the memory 23 is read out. This reading is continued until the end of reproduction, and the read key signals are applied to descrambling circuits 24 and 25.
The descrambling circuits 24 and 25 descramble the input scrambled audio and video signals based on the code pattern of the key signal.
In this case, if the scrambling method is based on the level change described above, the degree of amplification during the period in which the level is lowered is increased. When the scrambling method is based on rearranging the order of signals, the input signal is delayed and the order of the signals is returned to the original order during this delay time. The audio and video signals restored to their original form by the descrambling circuits 24 and 25 are applied to the receiver via output terminals 17 and 18. In addition, start signal S ₁
Alternatively, by adding a code corresponding to the program to the key discrimination signal _S2 , it may be used to locate the beginning of the tape during playback. Also memory 23
The key discrimination signal may be read out manually.

Next, various embodiments of the scrambling method will be described.

When performing scrambling, it is important to keep the contents of the scrambled signal as hidden as possible when it is received by a normal receiver, and to prevent the key code for descrambling from being easily deciphered. required to do so. on the other hand,
Since various signal processing is performed in a VTR during recording, various obstacles occur before the scrambled signal passes through the recording system and is recorded on the tape. This damage during recording remains as incomplete descrambling during playback, impairing image quality. Therefore, scrambled broadcasting as in the present invention is not possible.
In a system that records data once on a VTR, it is important that the scrambled signal passes through the recording system without problems, and especially in the case of home VTRs, it is necessary to increase the scrambling effect without disturbing the correlation between signals, and to avoid descrambling in the decoder. It is hoped that this will be easy. The various methods described below take the above points into consideration.

First, a video signal scrambling method will be described.

(1) V-flicker method This is the simplest method, and as shown in Figure 5, this is a method in which the level is changed on a per-field basis. In the illustrated case, the levels of the 4th, 7th, and 9th fields are lowered by 2 to 3 dB. Since the human eye is particularly sensitive to surface flicker, even slight variations in brightness can produce a scrambling effect. In the example shown in FIG. 5, a marker signal _S9 is inserted every 10 fields and scrambled using this as one period. Humans are most sensitive to flicker around 10 to 20 Hz, so the key code pattern can be determined using this period. In this case, only the Y signal may be used, but since the ratio with the C signal (chroma signal) changes temporarily, it is better to change the level of the C signal at the same ratio. In that case, the broadcasting station can scramble the Y+C composite signal as it is, and only the chroma will not be overmodulated. Furthermore, since the ACC operation is normally slow on the receiver side, it is not possible to follow the burst, and a scrambling effect of color flickering can also be added. Incidentally, if the burst signal is made to change in level, the scrambling process becomes simple, and if the burst signal level is kept constant, the amount of level change can be easily made large, although the process is somewhat complicated. On the other hand, VTRs are designed to allow for high-speed ACC response to account for hit fluctuations during playback, so recording and playback can be performed without any problems.

FIG. 6 shows an example of a scrambling circuit for performing the above flickering method.

Based on VD and HD extracted from the Y+C signal applied to the input terminal 31 by the synchronization separation circuit 32, a setup detection circuit 33, a marker signal generator 34, and a scramble code generator 35 are operated. When the switch 36 is opened or closed according to the scramble code, the setup detection circuit 3
In synchronization with the field detection by No. 3, the level of the Y+C signal is changed and scrambled according to the code pattern. This scramble signal is applied to an adder 37, and added to the sum output of the marker signal and the scramble code from the adder 38, and is selected. In this case, the scramble code becomes the key signal _S5 .

(2) Chroma flicker method This method scrambles the C signal by changing the phase of the burst signal on a field-by-field basis. Since this method modulates only the phase, even if the signal is passed through a VTR, it does not affect the S/N, etc., and does not disturb signal correlation, etc. Therefore, it is possible to improve the signal quality when descrambling. Moreover, it can be implemented without performing YC separation, which causes signal deterioration.

FIG. 7 shows an example of a scrambling circuit for carrying out the above method.

A burst signal is extracted from the Y+C signal applied to the input terminal 39 by a burst gate 40 and applied to an adder 41 . The extracted burst signals are shifted to 90°, 180°, and 180° by phase shifters 42 to 44, respectively.
The phase is shifted to 270° and applied to switch 45.
A scramble code generator 47 is driven by VD and HD from the synchronization separation circuit 46, and the switches 45 are sequentially switched in accordance with the scramble code. The burst signal whose phase has been sequentially shifted from 0° to 270° is added to the Y+C signal by an adder 41 and sent out.

When this circuit rotates the phase of the burst signal for each field, the APC of the receiver can usually follow each field, so the hue changes for each field. In this example, the hue changes randomly with the 12Hz chroma flicker, resulting in scrambled images. When recording on a VTR, various control systems can sufficiently follow the burst phase, so the burst phase is recorded on tape as is. Therefore, during playback, the original hue can be restored by decoding in the reverse sequence. In this method, at least two phases may be combined and switched, and more phases may be switched in various combinations. Specifically, as in method (1) above, a marker signal may be inserted every cycle of the combination.

(3) Signal replacement method In the example shown in Figure 8, the 1H period is divided into two, and the latter 1/2H portion is moved to the first half 1/2H portion of the next H period. When a signal obtained by this method is received by a normal television receiver, a normal image becomes a horizontally reversed screen as shown in FIG.

FIG. 10 shows an embodiment of a scrambling circuit according to the above method.

Input signal is 0.5H composed of CCD, BBD, etc.
By being delayed by the delay circuit 48, the scrambled signal shown in FIG. 8 is obtained. The CCD is driven by a clock from a clock generator 49 at n times the HD frequency. In addition, two switches 50, 51
is opened during the horizontal blanking period.

In order to further enhance the scrambling effect and to make descrambling more difficult, a regular signal may be inserted in each field into the scramble signal shown in FIG. 8.
If this insertion is performed using a key code, it will not be possible to decode it easily. To implement this method, for example, in FIG. 10, the input signal or a signal obtained by delaying the input signal by 1H and the 0.5H delay output are switched by a switch, and the input signal or the 1H delay output is switched at the insertion point. All you have to do is choose.

Alternatively, as shown in FIG. 11, the regular screen may be divided into four parts and their order may be changed. This case can be easily realized by appropriately combining 1/2 delay circuits, 1/4 delay circuits, etc.

(4) Ghost method As shown in Figure 12, this method creates a pseudo-ghost by delaying the input signal by about 1 μsec and switching the switch for each field.

(5) Time reversal method This is a method in which the signals written to the memory in 1H increments are read out in the opposite direction from when they were written, and this is combined with the regular field as one field unit.

FIG. 13 shows an embodiment of the scrambling circuit,
After the input signal is A/D converted, it is written alternately into two 1H memories via a switch that changes every 1H, so that when one is being written, the other is being read. At this time, when writing, the up-down counter is counted up, and when reading, it is counted down and read in the opposite direction. The read signal is taken out via a switch that changes every 1H and is D/A converted. This D/A output and the original input signal are alternately output one field at a time via a switch that changes over each field. When this scrambled signal is received by a normal receiver, the normal image and the horizontally reversed image are displayed twice on the screen.

Next, a method for scrambling audio signals will be described.

(1) Signal shuffling method As shown in FIG. 14, this is a method of shuffling the order of, for example, six fields.
In the case of audio, if the unit is too short, the content may be identified, so the length should be, for example, 6 fields (approximately 100 msec) or more. A marker signal is inserted to indicate the above-mentioned 6 field units, but this marker signal is the marker signal used for scrambling the video signal (for example, the 5th field unit).
The marker signal S ₉ ) shown in the figure may be used.

FIG. 15 shows a scrambling circuit for implementing the method of FIG. 14.

The BBD, which has a delay time of 6 fields, constantly writes and reads input audio signals using the clock marked in the VD of the video signal.
The read signal and the original audio signal are alternately selected every 12 fields by a switch. As a result, the 2nd, 4th, 6th... signals in FIG. 14 are taken out as they are, and the 1st, 3rd, 5th... signals are delayed and taken out. Note that the reordering pattern can take various forms.

(2) Time reversal method (5) of the video signal scrambling method described above.
(Fig. 13). For example, as shown in Fig. 15, 6 fields are written to the memory in units of 6 fields and then read out continuously in the reverse direction, or in reverse order according to a predetermined pattern. Read out in combination.

FIG. 17 shows an embodiment of the scrambling circuit, in which a 6-field memory is written in the up direction by an up-down counter and read out in the down direction. The read signal and the original signal are selected by a switch and output. The switching of this switch is performed at a timing corresponding to the scramble pattern shown in FIG.

As described above, according to the present invention, when receiving scrambled broadcasting in which a key signal for descrambling is added to the end of a scrambled program, it is not possible to view this in real time. It is possible to make it so that the correct program cannot be viewed unless a recording/reproducing device such as a VTR equipped with a decoder is used. Additionally, regardless of the type of VTR used, changes to the VTR can be kept to a minimum.

[Brief explanation of drawings]

1 and 2 are block diagrams showing an embodiment of the connection relationship between a VTR, a decoder, and a receiver, FIG. 3 is a diagram showing an embodiment of the signal arrangement of a scrambled broadcast signal according to the present invention, and FIG. 5 is a waveform diagram illustrating an embodiment of the scrambling method; FIG. 6 is a block diagram illustrating an embodiment of the scrambling circuit; FIG. 7 is a block diagram illustrating a modified example of the scrambling circuit; 8 is a waveform diagram showing a modified example of the scrambling method, FIG. 9 is a diagram of a television screen, FIG. 10 is a block diagram showing a modified example of the scrambling circuit, FIG. 11 is a diagram of a television screen, and FIGS. FIG. 13 is a block diagram showing a modified example of the scrambling circuit, FIG. 14 is a time chart showing a modified example of the scrambling method, FIG. 15 is a block diagram showing a modified example of the scrambling circuit, and FIG. 16 is a block diagram showing a modified example of the scrambling circuit.
17 is a time chart showing a modification of the scrambling method, and FIG. 17 is a block diagram showing a modification of the scrambling circuit. In addition, in the symbols used in the drawings, 1... VTR,
2...decoder, _S2 ...key discrimination signal, _S3 ...audio signal, _S5 ...key signal, _S7 ...video signal.

Claims (1)

[Claims] 1 means for recording and reproducing the scrambled television signal of a specific program; means for storing a key signal for descrambling added to the end of the specific program; and a means for storing a key signal for descrambling added to the end of the specific program; A television signal recording and reproducing apparatus comprising means for descrambling the television signal from the recording and reproducing means based on the read key signal.