FR2458874A1 - Footage recording on video tape - uses microprocessor to detect and process time data recorded on synchronising track - Google Patents

Abstract

To facilitate accurate measurement of video tape footage a time marking facility has been incorporated in French television transmissions, allowing recording on the video tape channel normally used for picture synchronisation of timing data identifying each sequence in the transmission. A fixed binary code occurs at the commencement of each frame as the first part of the data, and is identified by a microprocessor, incorporated in the playback circuit of the video recorder, as representing the synchronising pulse, in response to which the microprocessor immediately supplies the synchronising pulse to the TV receiver. The second part of each data set indicates, in successive frames, hours, tens of minutes, minutes, tens of seconds, and seconds. The microprocessor uses this data to compute elapsed time and puts it on an electronic display.

Description

 The present invention relates to a system for recording information of footages on a magnetic tape for recording television images.

 More particularly, the invention relates to a system for recording footing information on the track of the strip which is normally provided for recording the image synchronization pulses.

The popularization of television image recording devices has led manufacturers of mass-market video recorders to develop very simplified equipment without the sophisticated and expensive accessories that equip professional equipment. Thus, mass-market video recorders are currently provided with a mechanical counter whose indication represents neither the length of the tape, nor the duration of recording, but the number of turns of the reel supplying the cassette. This summary indication was sufficient for first generation devices whose recording capacity was limited to one hour of program. New devices that are capable or that will be capable of recording several hours of program require the use of better adapted and more precise systems.

The old image recording magnetic tapes capable of recording for about an hour included the video tracks, the servo track, a first sound track and the second sound track. According to the new standards published in the European journal of
Radio broadcasting, 4th edition, August 1975, pages 16 and 17, magnetic tapes with high recording capacities now only contain video tracks, the servo track and a single sound track.

 In addition, an automatic recording service for so-called "EPEOS" television programs has been developed, the description of which is given in the French review "Radiodiffusion-Télévision". In this EPEOS system, the precise reading of the trampling information identifying each sequence is necessary for the automatic search for a recorded program. However, this precise reading is obviously only possible if the information on footing is precise. With the tapes conforming to the old standards, the second sound track was used to record the toll information, but, with the tapes conforming to the new standards, this possibility can no longer be used.

 An object of the present invention is to provide a system for recording precise footing information using the servo track.

According to a characteristic of the invention, there is provided a system for recording trampling information on a magnetic tape for recording television images, the recording of trampling information being carried out on the track of the tape which is normally intended for recording synchronization pulses, in which, opposite each oblique track for recording a video image, a signal is recorded comprising two parts, the first part of which is fixed and the second represents slices of hourly data arranged in sequences, themselves arranged in a group, each group corresponding to the number N of television images per second and having its content changing every second.

According to another characteristic, in a television system at 25 frames per second, each group comprises a slice of data indicating the change of second, followed by four sequences, each sequence being composed of a slice of data-indicating the start of a sequence of a data section indicating the unit of the hour, a data section indicating the tens of minutes, a data section indicating the unit of the minute, a section of data indicating the tenth of the second, and a slice of data indicating the unit of the second.

 According to another characteristic, the modulation used for recording the trampling information being a displacement modulation by phase jumps preceded by a non-return to zero coding, the reading of the trampling information is carried out by counting the duration of the intervals between the changes of state of the raw signal read, then by comparison of the durations of the second and third intervals in a series of three or four intervals, the detection of a third interval longer than the second resulting in the detection of a " 1 "binary, the next interval then being considered as the first of a new series, while the detection of a third interval substantially of the same duration as the second previous results in the detection of a binary" O ", the next interval then being considered as the fourth in a series before the next series.

 According to another characteristic, the trampling information read from the tape is transmitted to a microprocessor which performs the counts and the duration comparisons, then the detections of the value of the binary element, then transmits to the television the resulting classic sync top. recognition of the fixed part of the data.

The characteristics of the present invention mentioned above, as well as others, will appear more clearly on reading the following description of an exemplary embodiment, said description being made in relation to the accompanying drawings, among which:
Fig. 1 is a schematic view of a portion of a television image recording tape,
Fig. 2 is a block diagram illustrating the circuits for recording footing information according to the invention,
Fig. 3 is a block diagram illustrating the circuits for reading footing information according to the invention,
Fig. 4 is a waveform illustrating the digital signals to be recorded,
Fig. 5 is a waveform of the actually recorded signals corresponding to the digital toll information signals.

Fig. 6 is a flow diagram illustrating a sequence of the program for reading the circuits of FIG. 3,
Fig. 7 is a flow diagram illustrating a second sequence of program for reading the circuits of FIG. 3, and
Fig. 8 is a flowchart illustrating a third sequence of program for reading the circuits of FIG. 3.

The strip of FIG. 1 conforms to the standards currently in force and includes the diagonal tracks 1 for recording the video, each line corresponding to the recording of a frame, track 2 for the recording of the sound and track 3 for the synchronization recording. It will be recalled that, on the synchronization track 3, a signal is recorded for each complete image, that is to say every two frames.

In the known bands, the synchronization signal is constituted by a burst of equidistant pulses and, between the synchronization signals, the track carries no information.

According to the system of the invention, a series of digital information is substituted for the simple burst of synchronization pulses which represents both the servo or synchronization information and the location or footing data. This digital information is entered as follows on track 3:
0111110 or a numeric combination representing the synchronization sequence, followed by a sequence of tracking data. The synchronization sequence which represents the servo information is in phase with the diagonal recording of the video on the magnetic tape. On reading, the demodulation of this information replaces the pulses intended to control the device.

The table below shows the organization of the recording, according to the invention, carried out on track 3.

Board
Frame No.Binary sequence Notes
1 ----- 011111001101 Second change indication
2 /// 011111001011 Indication of start of time sequence
3 01111100XXXX Units of hours
4 o1111100xxxx Tens of minutes
5 oiiiiioexxxx Units of minutes
6 01111100XXXXXX Tens of seconds
7 01111100XXXX Units of seconds
8 /// oiiiiioeioii Indication of start of time sequence
9 0111111100XXXXX Hour units
10 01111100XXXX Tens of minutes
11 01111100XXXX Units of minutes
12 01111100XXXX Tens of seconds
13 01111100XXXX Units of seconds
14 / / / 011111001011 Indication of start of time sequence
15 01111100XXXX Units of hours
20 / / / 011111001011 Indication of start of time sequence
25 01111100XXXX Units of seconds
1 - ~~~~ 011111001101 Second change indication
2 / / / 011111001011 Indication of start of time sequence
The recording was broken down into images whose numbers were chosen from 1 to 25 to represent a duration of one second. Image 1 is characteristic of the change of second, image 2 of the start of a time sequence, etc. It appears that in one second of recording the time sequence is repeated four times. The synchronization pulse is deduced from the combination 0111110 which precedes each setting data and is recognized by a logic circuit which will be seen below.

Fig. 2 shows the circuit 4 for recording footing information in relation to a video recorder 5, a camera 6 and a display device 7. The video recorder 5 receives the images to be recorded from the camera 6 by the link 8. It transmits, by the link 9, synchronization signals to the circuit 4 and receives, by the link 10, the signals to be recorded on track 3 of the tape, these signals constituting, as said above, the synchronization information and stamping.

 The recording circuit 4 is a microprocessor assembly which includes a central unit 11, a program memory 12, an interface 13, a counter 14 and an input / output circuit 15, plus a generator of time codes 16. Overall microprocessor, circuits 11 to 15 are interconnected by a conventional bus and we have not shown in FIG. 2 that functional links helping to understand how it works.

For example, the microprocessor can be a well-known INTEL 8085 circuit. The time code generator 16 is, in the example of embodiment described, constituted by two 7227B INTERSIL boxes which, starting from the pulses at 50 Hz (image synchronization top) and under the control of the microprocessor, supply the data sequences of marking OXXXX which follow the invariable synchronization sequence 0111110. The programmable counter 14 develops, under control of the central unit 11, the carrier signal. The interface 13, on the basis of the carrier signal received from 14 and the OXXXX data received from 15 to which is added the synchronization sequence, performs the serialization of the signals and the modulation of the carrier for recording by 10 on the tape. magnetic 5.

The display device 7 is connected by the link 17 to the input / output circuit 15, which, on the basis of the data produced in 16, delivers the signals OXXXX in parallel to both 7 and 13.

 In the interface 13, the modulation used is a displacement modulation by phase jumps preceded by non-return to zero coding.

The curve of FIG. 4 shows a message 011111001010 while the curve in FIG. 5 shows the corresponding signal recorded on the tape with the chosen modulation. The conversion between the binary signal and the modulated signal is done in the interface and does not need to be described in more detail.

 In fact, the central unit 11 receives the time codes of 16 and transmits them to the memory 12, in which are also written the codes for indication of change of seconds and indication of start of time sequence. As seen above, each time sequence is repeated four times in one second. It therefore appears that every second, part of the content of 12 varies according to the reading of 16 by 11, then, under the command of 11, the data from memory 12 are read towards the input / output circuit 15 which transmits them to 13 and 7.

The counter 14 provides the interface 13 with the carrier frequency Fp from the quartz frequency of the control unit 11. The carrier
Fp not being in synchronism with the image frequency, it is necessary to carry out a phasing of this carrier at each start of image to keep a constant position of the synchronization sequence with respect to the start of the image. For this purpose, the synchronization ticks of the video recorder 5 are sent to the counter 14, by 9 to reset it with each image.

Fig. 3 shows the circuit 18 for reading footing information in relation to the video recorder 5, the display device 7 and a television set 19. The video recorder 5 transmits the images to be displayed towards the television set 19. It transmits, by the link 20, the signals read on track 3 of its band to circuit 18 and receives, by link # 21, from circuit 18 the synchronization signals retransmitted by 5 to 19.

 The read circuit 18 is a microprocessor assembly which, like the microprocessor of the recording circuit 4, comprises a central unit 11, a memory 12, an interface 13, a counter 14 and an input / output circuit 15. In practice, this which distinguishes 18 from 4 is the program used in the microprocessor. The interface 13 receives, in this configuration, a clock frequency from the central unit 11 and, by the link 20, the modulated signals of track 3 of the video recorder 5, that is to say the signals symbolized by the curve of Fig. 5. The modulated signals are sampled at clock frequency and the sampling highlights the edges of change of state from 1 to O or from O to 1 of the modulation. Each change is characterized by an INT request (for interruption) emitted by the interface 13 to the central unit there. This INT request is reset to its initial state by an INTA response from 11 to 13.

When the central unit 11 receives an INT request, it executes a time measurement program, which corresponds to that of the flowchart of the
Fig. 7, to measure the time elapsed between two INT requests and, depending on the measurement, the central unit decides on the logic state 1 or O of the modulation.

 In practice, the decoding of this modulation results in a signal sent by 11 to 15 to be retransmitted by 21 to 5 and by a time sequence sent to 15 to be retransmitted to the display device 7.

Before describing the flowcharts in Figs. 6 to 8, we will briefly recall the principles of modulation used by referring again to Figs. 4 and 5.

The modulation is applied to a carrier of frequency Fp = 2Fo, where Fo is the frequency of the binary element of the modulating signal. Non-return to zero modulation is characterized by maintaining 1 or 0 in the presence of a binary element 1 of the modulating signal. Consequently, demodulation consists in detecting the long steps of the modulated signal, which is done by comparing the durations of the successive steps. As the stages are delimited by changes of state, which give rise to INT requests to the central unit 11, the detection therefore passes by time measurements between successive INTs.

In practice, in the example of embodiment described, if the duration of a level exceeds 7/5 of the duration of the previous level, this level is considered to be long. The measurement of these levels is carried out by a programmable counter A8253 which operates at the clock frequency Fp / 5 for one level, then at the clock frequency Fp / 7 for the next level, in sequences of 3 or 4 levels , as we will see below.

 As the row of numbers under the curve in Fig. 5, each sequence comprises a level N0i, a level N02, a level N03 and possibly a level N04. Each N01 level is not counted, that is to say a time measurement. Each level N02 is measured with a frequency Fp / 5 while each level N03 is measured with a frequency Fp / 7. Finally, each level N04 is not measured.

 The operating principle of the comparison is as follows using an up-down counter. During a stage N02, the counter is loaded at a given frequency, then during stage N03, it is discharged at a slightly slower frequency. If the two stages are practically the same length, at the end of stage N 3, the counter will not be fully discharged. If the NO 3 stop is almost twice as long as the previous one, the counter will be fully discharged before the end of the N03 stop.

The complete unloading or not of the counter indicates the presence or not of a long stop, that is to say a 1 in the initial modulation. Note that this comparative evaluation makes the measurement independent of the speed fluctuations of the VCR.

Fig. 6 shows the flow diagram of the main program of the control unit 11, FIG. 7 shows the flowchart of a long interrupt program and FIG. 8 shows the flow diagram of a short interrupt program.

The short interruption program involves three counters, either an E counter which counts the stages and takes the values 1, 2, 3 and possibly 4, a CTRO counter which divides the main clock of the unit by 5 or 7 central 11, and a counter CTR1 which counts the number of pulses emitted by the counter CTRO during the second and third stages of each sequence of counter E.

 Initially, the main program, Fig. 6, described a part called "initializations", during which the boluses of the microprocessor are initialized, then goes into the standby position called "hauled" by authorizing interruptions. When a modulation state change edge is transmitted by the interface 13 to the central unit 11, it triggers, by the microprocessor interrupt command, the short interrupt program, FIG. 8.

The short interruption program begins with the stop of the counter
CTRO, which initializes the counter CTR1 and increments the counter # E. If one supposes that initially E was at zero, the counter E passes to state 1, from where the decision "no" for the test "E = 4 ", so that the result is a new authorization of the interruptions, maintenance of the carry or" carry "at 0, then a return to the main program of FIG. 6, by point A.

The main program is placed in the so-called "hait" waiting position.

When the next edge of modulation state change is transmitted, it triggers the short interrupt program again, Fig. 8, the counter
E then being at 1 and the CTRO counter still stopped.

 The short interrupt program begins by keeping CTRO at 0, then passes the counter E to 2. The test "E = 2" is then positive, which causes the counter CTR1 to be loaded at its maximum value FF, then we load the accumulator at 5 so that the CTRO counter divides by 5. The CTRi'and CTRO counters are then launched and, with a new interruption authorization, maintaining the hold at O, we return to the main program by point A.

 The main program returns to the standby position again. When the next edge of modulation state change is transmitted, it triggers the short interrupt program again, Fig. 8, the counter E is then at 2 and the counter CTRO is being counted.

The short interrupt program begins by stopping the counter
CTRO, then passes the counter E to 3. The test "E = 3" is then positive, which entails the reading of the complement of the account reached by the counter CTR1, the storage of the value read, then the loading of CTR1 with this value, finally the accumulator is charged at 7 so that the CTRO counter divides by 7. The CTR1 and CTRO counters are then launched again and, with a new authorization to interrupt, maintaining the hold at Ot we return to the main program at point A.

 The main program is still in the waiting position. When the next edge of modulation state change is transmitted, before the counter CTRi reaches O, it again triggers the short interrupt program, Fig. 8, the counter E then being at 3.

The short interrupt program stops the CTRO counter, changes the counter E to 4, then the test "E = 4" being positive, the counter E is reset to O, the hold is kept at O, and we return to the program main at point B.

When the counter CTR1 reaches 0, before the arrival of the next edge, it then triggers the long interrupt program, Fig. 7.

The long interrupt program resets the counter E to 0, sets the hold back to 1. Then we return to the main program at point B.

 On returning to the main program at point B, whether the restraint is at o or 1, the binary element of restraint is entered into the accumulator by shifting it. When the sequence of ebs in the accumulator is 0111100XXXX, the test "= 011110" on the first six ebs is positive, which triggers the output of a synchronization signal, then the output of OXXXX data and finally the delivery of the carry at O, when, after an offset in the accumulator, the test "= 011110" is negative, the carry is reset to 0.

It therefore appears that the above program makes it possible to distinguish the 3rd long or short steps, that is to say to restore the initial modulation signal.

Claims (4)

HEVCDICATIONS N of television images per second and having its content changing every second. lv System for recording trampling information on a magnetic tape for recording television images, the recording of trampling information being carried out on the track of the strip which is normally intended for recording synchronization pulses. , characterized in that, opposite each oblique track for recording a video image, a signal is recorded comprising two parts, the first part of which is fixed and the second represents slices of time data arranged in sequences, themselves arranged in a group, each group corresponding to the number  2) System according to claim 1, characterized in that, in a television system at 25 images per second, each group comprises a data segment indicating the change of second, followed by four sequences, each sequence being composed of a segment data indicating the start of a sequence, a data section indicating the unit of the hour, a data section indicating the tens of minutes, a data section indicating the unit of the minute, a slice of data indicating the tens of seconds, and a slice of data indicating the unit of seconds. 3) System according to claim 1 or 2, characterized in that, the modulation used for recording the trampling information being a displacement modulation by phase jumps preceded by a coding in non-return to zero, the reading of the information trampling is performed by counting the duration of the intervals between the changes in state of the raw signal read, then by comparing the durations of the second and third intervals in a series of three or four intervals, detecting a third longer interval as the second causing the detection of a binary "1", the next interval then being considered as the first of a new series, while the detection of a third interval substantially of the same duration as the second preceding incoming detection a binary "O", the next interval then being considered as the fourth in a series before the next series.  4) System according to claim 4, characterized in that, the trampling information read from the strip is transmitted to a microprocessor which performs the counts and the duration comparisons, then the detections of the value of the binary element, then transmits on the television the classic sync top resulting from the recognition of the fixed part of the data.