JPS647719B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a video tape recorder switching method for selectively switching a plurality of video tape recorders to obtain one continuous video signal.

In general, regenerated signals from video tape recorders (hereinafter referred to as VTRs) contain time base errors such as jitter, and broadcasting stations and video software supply companies that handle high-quality video signals generally In this case, a time base correction device (time base collector) is connected to the VTR to remove the above time base error from the reproduced video signal.
Editing, broadcasting, etc. This time axis correction device adjusts the phase of the synchronization signal of the playback video signal from the VTR with respect to the reference synchronization signal predetermined within the broadcasting station, and depending on the model, it can be used within several hours. It also has functions such as performing dropout correction, and is closely tied to the VTR, so the pair of VTR and time axis correction device is often treated as a single unit.

Therefore, when switching and transmitting playback signals from multiple VTRs, or when selectively recording and playing between multiple VTRs, it is necessary to
Since it is necessary to provide one time axis correction device for each VTR, a plurality of expensive time axis correction devices are required, resulting in extremely high equipment costs.

The present invention has been made in view of such conventional circumstances, and is intended to be applied to high-grade
Focusing on the fact that when multiple VTRs are used to process a single system of video signals, one of the VTRs is normally in use, one time axis correction device is used to process the multiple VTRs. The purpose of the present invention is to provide a video tape recorder switching method that enables a significant cost reduction by selectively switching between VTRs.

That is, the feature of the video tape recorder switching method according to the present invention is that a plurality of video tape recorders are connected to one time axis correction device via a selection switching circuit section, and an odd number obtained from this time axis correction device is・The synchronization of the plurality of video tape recorders is controlled in accordance with the advanced synchronization signal pulse which is advanced by a predetermined horizontal time from the vertical/horizontal composite synchronization signal of the even field discrimination pulse and the time axis corrected video output signal. Selection switching of the selection switching circuit section is performed at a timing within or near the vertical blanking period of the video signal based on the composite synchronizing signal pulse of the odd/even field discrimination pulse obtained from the time axis correction device and the video output signal. This is to perform a switching operation.

Below, as an example of the present invention, two
The case of switching and reproducing VTRs will be explained with reference to the drawings.

Figure 1 shows the overall block diagram, with two
VTRs 11 and 12 and one time axis correction device 10 are used. The first VTR 11 outputs a reproduced video signal VS1 and a dropout detection signal DO1, and the second VTR 12 similarly outputs a reproduced video signal VS2 and a dropout detection signal DO2. These playback video signals VS1, VS2
are supplied to the switching terminals a and b of the switching switch 21 in the VTR selection switching circuit section 20, and the dropout detection signals DO1 and DO
2 are supplied to switching terminals a and b of a switching switch 22 in the VTR selection switching circuit section 20, respectively. The output signals selected by these switches 21 and 22 are output to amplifiers 23 and 22, respectively.
24, the reproduced video signal VS and dropout detection signal DO are sent to the time axis correction device 10. From this time axis correction device 10,
A re-corrected video output signal VO that has been subjected to time axis correction such as jitter correction and dropout correction is output, and a composite sync signal (composite sync signal) that is a synchronization signal in the video output signal VO is output as a synchronization-related signal. ) CS, an advanced synchronization signal AS that serves as a reference synchronization signal for the VTR, and a frame pulse signal FP for switching between even and odd fields are output. Then, the composite synchronization signal CS and frame pulse signal FP are
The advanced synchronization signal AS and frame pulse signal FP are sent to the switch switching control circuit 25 in the VTR selection circuit section 20, and the advanced synchronization signal AS and frame pulse signal FP are sent to the first and second VTR 1.
Sent to 1 and 12. Switch switching control circuit 25
From then on, the switch switching pulse SP is the switching switch 2.
1 and 22, and these changeover switches 2
1 and 22 are switched and controlled. In addition, the amplifier 23, 2
4 is for amplifying the video signal and dropout signal to a specified input level to the time axis correction device 10.

In the above configuration, two VTRs 11,
12 is driven and controlled by an advanced synchronization signal AS and a frame pulse signal FP, which are control signals from one time axis correction device 10, and
Playback video signals from these VTRs 11 and 12
Switching between VS1 and VS2 is based on the reference composite synchronization signal CS and frame pulse signal FP from the time axis correction device 10.
This is performed at a timing during which no image is displayed, such as within or near the vertical blanking period of VS2. Note that the playback video signal VS1,
The switching timing of VS2 is determined by the time axis correction device 10.
The determination may be made based on the advanced synchronization signal AS from .

A specific example of a circuit configuration for performing such an operation is shown in FIG. In the block circuit diagram of FIG. 2, an input terminal 31 is supplied with a composite synchronization signal CS which becomes a synchronization signal of the video output signal VO after the time axis correction process. for example,
When transitioning from an even field to an odd field, that is, from one field to another in color framing, a composite synchronizing signal CS as shown in FIG. Ru. In this composite synchronization signal CS shown in FIG. ... is attached. At this time, 3H with numbers 1 to 3 is the front equalizer pulse period, 3H with numbers 4 to 6 is the vertical synchronization signal period,
3H with numbers 7 to 9 is the rear equalizer pulse period. Next, the monomulti circuit is triggered by the falling edge of the composite synchronization signal CS in Figure 3A, and has a pulse width τ that is shorter than 1/2 of the horizontal period H and longer than the pulse width of the horizontal synchronization pulse. A pulse signal, for example, as shown in FIG. 3B, has a pulse width τ
outputs a pulse signal MS of, for example, 17 μsec, and sends it to a comparison circuit (or sampling circuit) 33. A synthesized synchronization signal CS from the input terminal 31 is sent to this comparison circuit 33, and the above pulse signal
Detecting the level of the composite synchronizing signal CS at the falling edge of MS, that is, at a time delayed by the pulse width τ (for example, 17 μsec) from the falling edge of the composite synchronizing signal CS,
A comparison signal as shown in FIG. 3C, which has this level inverted, is output. The comparison signal shown in FIG. 3C is taken out from the output terminal 34 as a vertical synchronizing signal and is sent to the flip-flop circuit 35. Here, the third
The pulse signal MS shown in FIG. Therefore, from the flip-flop circuit 35, for example, the switching timing is set at the rising edge of the second pulse signal MS after the rising edge of the vertical synchronizing signal (C in FIG. A frame pulse signal FP as shown in FIG. 3D, which has a low level L'' on the side, is obtained. This frame pulse signal FP is obtained. This frame pulse signal FP is taken out from the output terminal 37, sent to the delay circuit 38, delayed by, for example, 5H, and taken out from the output terminal 39 as a switch switching pulse SP as shown in FIG. 3E. This delay circuit 38 becomes the main part of the switch switching control circuit 25 shown in FIG. It is necessary to supply The other circuit sections shown in FIG. 2 are provided within the time base correction device 10 shown in FIG.

Next, Fig. 3F shows the above advanced synchronization signal.
AS is advanced (earlier in time) by, for example, 4H with respect to the composite synchronization signal CS in FIG. 3A. This advanced synchronization signal AS is
This is a signal for synchronous control of VTRs 11 and 12,
Control is performed by the servo mechanisms of the VTRs 11 and 12 so that the synchronization signals of the reproduced video signals VS1 and VS2 match the advanced synchronization signal AS.
Therefore, during normal operation, the time axis correction device 1
The synchronization signal of the video signal VS input to 0 becomes almost equal to the advanced synchronization signal AS, and by performing signal processing such as various corrections while delaying this by the above-mentioned 4H inside the time axis correction device 10, A video output signal VO whose synchronization signal is the composite synchronization signal CS from which fluctuations in the time axis and phase have been removed is obtained. The switching timing of the switch switching pulse SP in FIG. 3E is within the vertical blanking period of this advanced synchronization signal AS,
Playback video signal VS1 from VTR11, 12,
Switching can be performed without affecting the part of VS2 that is actually displayed as an image.

These Figures 3A to 3F are for explaining the switching timing when transitioning from an even field to an odd field, but the switching timing when transitioning from an odd field to an even field is shown in Figure 4. It will look like A to F. 4A to 4F correspond to FIG. 3A to F, respectively, and the vertical synchronization signal is different from the horizontal synchronization signal.
Since it is the same as FIGS. 3A to 3F except for the deviation by 0.5H, the explanation will be omitted.

In the case of a color video signal, it is necessary not only to have the continuity of the odd and even fields mentioned above, but also to make the phase of the color subcarrier signal continuous, so synchronization is performed at four field cycles from field to field. So-called color framing is necessary. That is, in a monochrome video signal, for example, the field of the video signal VS1 can be followed by the field of the video signal VS2, or either field, but in the case of a color video signal, the field can be followed by a field of the video signal VS2. The fields must be continuous.

This kind of color framing was also taken into consideration.
When changing the selection of the VTR, the counter 36 shown in FIG. 2 is used to determine the field .about., and the frame pulse signal FP shown in FIG. It is sufficient to use the color frame pulse signal CFP.

In addition, the playback video signal of the first VTR 11 is
When recording on the second VTR 12, the video output signal VO of the time axis correction device 10 is transferred to the second VTR 12.
2 and control the synchronization of the second VTR 12 using the composite synchronization signal CS.

As is clear from the above explanation, according to the switching method of the present invention, the switching timing for selectively switching two or more VTRs is set to a portion that does not appear on the screen during or near the vertical blanking period. Because the settings are set, the image is not affected by switching between VTRs, and the effect is essentially the same as connecting multiple time axis correction devices to each VTR, resulting in a significant cost reduction. You can aim for down.

Note that the present invention is not limited to the above embodiment; for example, in the embodiment, two VTRs are used.
I explained the case of using 11 and 12, but
For example, by increasing the number of switching terminals of the switching switches 21 and 22 of the VTR selection switching circuit section 20, it is possible to easily realize the use of three or more VTRs.

[Brief explanation of drawings]

The figures all show embodiments according to the present invention; FIG. 1 is a block diagram showing the overall configuration, FIG. 2 is a block circuit diagram showing the specific circuit configuration of the main part, and FIG.
-F are time charts for explaining the switching timing when moving from an even field to an odd field, and FIGS. 4A to 4F are time charts when moving from an odd field to an even field. 10... Time axis correction circuit, 11, 12...
VTR (video tape recorder), 20...VTR selection switching circuit section, 21, 22...Switching switch, 2
5...Switch switching control circuit.

Claims (1)

[Claims] 1 Connect multiple video tape recorders to one time axis correction device via the selection switching circuit section,
The plurality of video tapes are controlled in accordance with the advanced synchronization signal pulse, which is a predetermined horizontal time ahead of the vertical/horizontal composite synchronization signal of the odd/even field discrimination pulse obtained from the time base correction device and the time base corrected video output signal. In addition to controlling the synchronization of the recorder, the timing within or near the vertical blanking period of the video signal is based on the composite synchronization signal pulse of the odd/even field discrimination pulse obtained from the time axis correction device and the video output signal. A switching method for a video tape recorder, characterized in that the selection switching circuit section performs a selection switching operation.