JP4207571B2 - Video playback device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a video playback apparatus that plays back video, and in particular, has a DT head for variable speed playback, and when a vertical sync pulse for playback of video information is missing, this is interpolated based on the head height. The present invention relates to a video playback device that plays back video.
[0002]
[Prior art]
A DT head (dynamic tracking head) is used as a variable speed playback head of a video tape recorder. The DT head is installed on a rotating drum, and a head chip is placed on a piezoelectric element such as a bimorph. By applying a predetermined voltage to the piezoelectric element, the head height can be changed so that the track can be followed even during variable speed reproduction.
[0003]
Conventionally, various improvements such as an improvement in reproduction image quality at the time of variable speed reproduction have been made in a video reproduction apparatus using such a DT head (for example, Patent Document 1).
Here, a conventional video playback apparatus for playing back video will be described.
[0004]
FIG. 3 is a configuration diagram of a conventional video reproduction apparatus.
The video playback device 20 includes a DT head 21a, 21b that plays back recorded information on the magnetic tape 50, a video signal processing unit 22 that processes video signals, a DT head control unit 23 that controls the DT heads 21a, 21b, And a reference signal generator 24 for generating a reproduction reference signal.
[0005]
The DT heads 21a and 21b reproduce recorded information by scanning a recording track on the magnetic tape 50 wound around a rotating drum. The DT heads 21a and 21b are provided at positions where the rotating drums face each other, and are switched every 180 ° in synchronization with the rotation of the rotating drum by the reproduction reference signal, and one DT head always scans the recording track. .
[0006]
The video signal processing unit 22 receives and reproduces the reproduction RF signal output from the DT heads 21a and 21b and reproduces it as a video. Further, a vertical synchronization pulse (hereinafter referred to as a reproduction V pulse) and a horizontal synchronization pulse (hereinafter referred to as a reproduction H pulse) are extracted from the reproduction RF signal, demodulated, and transmitted to the DT head controller 23. The vertical synchronization signal at the time of the video reproduction process in the video signal processing unit 22 is a vertical synchronization pulse regenerated by the DT head control unit 23 without using the reproduction V pulse (hereinafter referred to as a V pulse to distinguish it from the reproduction V pulse). ) Is used. This is because when the reproduction V pulse is lost due to a recording abnormality or the like, the current V pulse must be generated by interpolation based on the phase of the previous V pulse. In the case of variable speed reproduction, the DT head is used as described above. Since the head heights of 21a and 21b change, this is possible because only the DT head control unit 23 that controls the head.
[0007]
The DT head control unit 23 controls the height of the DT heads 21a and 21b in accordance with the switching of the DT heads 21a and 21b to be reproduced and the reproduction speed so as to follow the track. Further, the V pulse is regenerated from the height of the DT heads 21a and 21b based on the reproduction V pulse and reproduction H pulse sent from the video signal processing unit 22. Further, when the reproduced V pulse is lost without being reproduced due to a recording abnormality or a head clog, the current V pulse is predicted and interpolated based on the phase of the previous V pulse and the current DT head height.
[0008]
Each unit is controlled by a system controller (not shown) that controls the entire device.
Hereinafter, the operation of the conventional video reproduction apparatus 20 will be described using a timing chart.
[0009]
FIG. 4 is a timing chart for explaining the operation of the conventional video reproduction apparatus.
Here, the reference frame pulse and the head switching pulse for switching the DT heads 21a and 21b synchronized with the reference frame pulse are signals that are collectively used as a reproduction reference signal in FIG.
[0010]
When a reproduction RF signal is input from the DT heads 21a and 21b, one screen is composed of data for one field, and the reproduction V pulse recorded near the head of the field is extracted by the video signal processing unit 22. At this time, time t10 is generated from the edge of the reference frame pulse or the head switching pulse to the rise of the reproduction V pulse. This is a time resulting from the fact that the height of the DT heads 21a and 21b entering the recording track always fluctuates because the phase of the magnetic tape 50 is not locked to the reproduction reference signal during variable speed reproduction by the DT heads 21a and 21b. is there.
[0011]
When the video signal processing unit 22 can correctly extract the playback V pulse from the playback RF signal, the DT head control unit 23 is interrupted at the rising edge of the playback V pulse sent from the video signal processing unit 22. Here, the DT head controller 23 measures the time t11 with a clock counter and generates a falling edge of the V pulse. Next, the time t12 is measured by the clock counter, and the rising edge of the V pulse is generated. After this rising edge generation, the time indicated by time t13 is measured by counting the number of reproduction H pulses.
[0012]
When the next reproduction V pulse is sent correctly, the DT head control unit 23 is interrupted again at the rising edge, and the DT head control unit 23 stops counting the reproduction H pulse, and clocks at times t11 and t12. A V pulse is generated by counting. However, as shown in the figure, when the reproduction V pulse is lost, since the DT head control unit 23 is not interrupted, the DT head control unit 23 counts a predetermined number of reproduction H pulses (including fluctuation range prediction at time t10). At the end of counting, a falling edge of the predicted V pulse is generated. The video signal processing unit 22 reproduces video using the predicted V pulse as a vertical synchronization signal.
[0013]
It should be noted that there is no horizontal sync pulse in a section where there is no reproduction RF, such as the time width of time t14. Therefore, the video signal processing unit 22 sends a reproduction H pulse interpolated based on the immediately preceding horizontal synchronization pulse train to the DT head control unit 23.
[0014]
[Patent Document 1]
JP-A-10-241130 (paragraph numbers [0018] to [0088], FIG. 1)
[0015]
[Problems to be solved by the invention]
However, it is difficult to obtain sufficient accuracy for the period of the reproduction H pulse to be interpolated, and as a result, there is a problem that the edge timing of the predicted V pulse deviates from the phase that should be supposed.
[0016]
If the reproduction V pulse is missing several consecutive times, the phase shift of the predicted V pulse is not a problem. However, the phase shift accumulates over a long period of time, the phase of the predicted V pulse flows with respect to the playback reference signal, and the synchronization of the vertical sync signal (hereinafter referred to as V sync shift) occurs in the playback image.
[0017]
As a result, for example, when reproducing a magnetic tape in which a vertical synchronization pulse is not accurately recorded for only one field due to a recording abnormality or the like, there is no problem if the tape speed is high to some extent, but an attempt is made to reproduce a still image in that field. As a result, there is a problem in that an image that is out of sync with V continues to be reproduced. Furthermore, since such an image is suddenly output, there is a problem that the user is worried about the failure of the video tape recorder, the damage of the tape, and the like, and is anxious.
[0018]
The present invention has been made in view of these points, and an object of the present invention is to provide a video reproduction apparatus that prevents V images from being out of sync with each other.
[0019]
[Means for Solving the Problems]
In the present invention, in order to solve the above-mentioned problem, in a video playback apparatus that plays back by interpolating a vertical synchronization pulse for playback of video information when it is missing, the vertical synchronization for playback of the video information A vertical sync pulse missing detector that detects missing pulses and counts the number of missing pulses, an alternative vertical sync pulse generator that generates an alternative vertical sync pulse having a constant phase with respect to the reproduction reference signal, and a missing vertical sync pulse When the number of missing parts does not reach the predetermined number, the dynamic tracking head control unit uses the previous vertical synchronization pulse as a reference and the fluctuation width of the vertical synchronization pulse according to the head height during variable speed reproduction. The vertical synchronization pulse predicted by counting the horizontal synchronization signal in consideration of the above is used for reproduction of the video information, and when the number of missing parts reaches a predetermined number, it is predicted The serial vertical synchronization pulses instead, a switching unit for switching as used for reproducing the substitute vertical synchronizing pulses the video information, the video reproducing apparatus characterized by having provided.
[0020]
According to the above configuration, when a predetermined number of vertical synchronization pulses are lost, the alternative vertical synchronization pulse generated by the alternative vertical synchronization pulse generation unit by the switching unit is replaced with a synchronization signal at the time of video reproduction instead of the predicted vertical synchronization pulse. To prevent the V-synchronization of the reproduced image from being lost.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
Here, a video playback apparatus applied to a video tape recorder capable of variable speed playback will be described as an embodiment of the present invention.
[0022]
FIG. 1 is a configuration diagram of a video reproduction apparatus according to an embodiment of the present invention.
The video playback apparatus 10 according to the embodiment of the present invention controls the DT heads 11a and 11b that play back recorded information on the magnetic tape 50, the video signal processing unit 12 that processes video signals, and the DT heads 11a and 11b. DT head control unit 13, reference signal generation unit 14 for generating a reproduction reference signal, alternative V pulse generation unit 15 for generating an alternative V pulse to be described later, and reproduction V pulse missing detection for counting the number of missing reproduction V pulses And a switching unit 17 for switching between the output of the V pulse from the DT head control unit 13 and the output of the alternative V pulse.
[0023]
The DT heads 11a and 11b scan recording tracks on the magnetic tape 50 wound around a rotating drum (not shown) and read recording information. The DT heads 11a and 11b are provided at positions where the rotating drums face each other, and are switched every 180 ° in synchronization with the rotation of the rotating drum by the reproduction reference signal, and one DT head always scans the recording track. .
[0024]
The video signal processing unit 12 receives and reproduces the reproduction RF signal output from the DT heads 11a and 11b and reproduces it as a video. Further, a reproduction V pulse and a reproduction H pulse are extracted from the reproduction RF signal, demodulated, and sent to the DT head control unit 13. As a synchronization signal in video reproduction processing, V pulses regenerated by the DT head control unit 13 are used without using reproduced V pulses.
[0025]
The DT head control unit 13 controls the height of the DT heads 11a and 11b in accordance with the switching of the DT heads 11a and 11b to be reproduced and the reproduction speed so as to follow the track. Further, the V pulse is regenerated from the height of the DT heads 11a and 11b based on the reproduction V pulse and reproduction H pulse sent from the video signal processing unit 12. In addition, when the reproduction V pulse is lost without being reproduced due to a recording abnormality or a head clog, the current V pulse is predicted based on the phase of the previous V pulse and the current DT head height, and the predicted V pulse Generate and interpolate.
[0026]
The reference signal generation unit 14 generates a reproduction reference signal used for switching the DT heads 11a and 11b.
The alternative V pulse generator 15 generates an alternative V pulse that always maintains a constant phase with respect to the reproduction reference signal. The alternative V pulse generator 15 can be realized by mono-multi (monostable multi-vibrator) or the like.
[0027]
The reproduction V pulse missing detector 16 detects missing reproduction V pulses and counts the number of missing data. The reproduction V pulse missing detector 16 can be realized by a counter or the like.
The switching unit 17 outputs an alternative V pulse to the video signal processing unit 12 instead of the predicted V pulse when the reproduction V pulse loss detection unit 16 reaches the predetermined number of missing reproduction V pulses. Switch to.
[0028]
Each unit is controlled by a system controller (not shown) that controls the entire device.
Hereinafter, the operation of the video reproduction apparatus 10 according to the embodiment of the present invention will be described using a timing chart.
[0029]
FIG. 2 is a timing chart for explaining the operation of the video reproduction apparatus according to the embodiment of the present invention.
Here, the reference frame pulse and the head switching pulse for switching the DT heads 11a and 11b are signals used as reproduction reference signals in FIG.
[0030]
The alternative V pulse generator 15 detects the edge of the reproduction reference signal (reference frame pulse or head switching pulse), and always uses a constant phase with respect to this edge, and a predetermined time width indicated by time t1 in FIG. To generate a falling edge of an alternative V pulse. Further, a predetermined time indicated by time t2 is measured by the clock counter, and the rising edge of the alternative V pulse is generated.
[0031]
When a reproduction RF signal is input from the DT heads 11a and 11b, one screen is composed of data for one field, and therefore the reproduction V pulse recorded near the head of the field is extracted by the video signal processing unit 12. At this time, a time width of time t3 occurs from the edge of the reference frame pulse or the head switching pulse to the rise of the reproduction V pulse. This occurs because the phase of the magnetic tape 50 is not locked to the reproduction reference signal during variable speed reproduction by the DT heads 11a and 11b, and the height at which the DT heads 11a and 11b enter the recording tracks always fluctuates.
[0032]
When the video signal processing unit 12 can correctly extract the reproduction V pulse from the reproduction RF signal, the DT head control unit 13 is interrupted at the rising edge of the reproduction V pulse. Here, the DT head controller 13 measures a predetermined time indicated by time t4 with a clock counter, and generates a falling edge of the V pulse. Next, a predetermined time indicated by time t5 is measured with a clock counter, and a rising edge of the V pulse is generated. After this rising edge generation, the time width indicated by time t6 is measured by the pulse count of the reproduction H pulse.
[0033]
When the next reproduction V pulse is sent accurately, the DT head control unit 13 is interrupted again at the rising edge, and the DT head control unit 13 stops the reproduction H pulse count and clocks at times t4 and t5. A V pulse is generated by counting. However, as shown in the figure, when the reproduction V pulse is missing, the DT head control unit 13 is not interrupted, so the DT head control unit 13 counts a predetermined number of reproduction H pulses (including fluctuation range prediction at time t3). At the end of counting, a falling edge of the predicted V pulse is generated. The video signal processing unit 12 reproduces the video using the predicted V pulse as a synchronization signal.
[0034]
It should be noted that there is no horizontal sync pulse in the interval where there is no reproduction RF signal as at time t7. Therefore, the video signal processing unit 12 sends a reproduction H pulse interpolated based on the immediately preceding horizontal synchronization pulse train to the DT head control unit 13.
[0035]
Further, in the video reproduction apparatus 10 according to the embodiment of the present invention, when the reproduction V pulse is missing, the reproduction V pulse missing detection unit 16 detects the lack of the reproduction V pulse, and counts up every time one pulse is missing. And count. When the result of counting by the reproduction V pulse missing detection unit 16 reaches a predetermined value, the reproduction V pulse missing detection unit 16 sends a signal to that effect to the switching unit 17.
[0036]
Upon receiving this signal, the switching unit 17 switches from the output of the predicted V pulse generated by interpolation by the DT head control unit 13 to the output of the alternative V pulse generated by the alternative V pulse generation unit 15. The video signal processing unit 12 reproduces the video using the alternative V pulse instead of the predicted V pulse as the vertical synchronization signal.
[0037]
Here, the predetermined value at the time of switching to the output of the alternative V pulse is appropriately adjusted to such an extent that the reproduced image does not lose V synchronization. For example, switching is performed with about 5 to 10 pulses.
[0038]
Thereafter, when an accurate reproduction V pulse is input again, the count value of the reproduction V pulse missing detector 16 is reset. The video signal processing unit 12 reproduces video using the V pulse generated by the DT head control unit 13.
[0039]
In this way, when a predetermined number of reproduction V pulses are missing, an alternative V pulse that always has a constant phase with respect to the reproduction reference signal is used as a synchronization signal instead of a predicted V pulse that causes a phase shift. However, it is possible to prevent the V synchronization from being lost. Therefore, the user is not worried.
[0040]
【The invention's effect】
As described above, in the present invention, an alternative vertical synchronization pulse having a constant phase with respect to the reproduction reference signal is generated, and when the number of missing vertical synchronization pulses reaches a predetermined number, instead of the predicted vertical synchronization pulse, This alternative vertical sync pulse was used.
[0041]
Thus, when a predetermined number of vertical synchronization pulses are missing, instead of the predicted vertical synchronization pulse that causes a phase shift, an alternative vertical synchronization pulse that has a constant phase with respect to the reproduction reference signal is used as a synchronization signal. It is possible to prevent the reproduced image from being left out of V synchronization. Therefore, the user is not worried.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a video reproduction apparatus according to an embodiment of the present invention.
FIG. 2 is a timing chart for explaining the operation of the video reproduction apparatus according to the embodiment of the present invention.
FIG. 3 is a configuration diagram of a conventional video reproduction apparatus.
FIG. 4 is a timing chart for explaining the operation of a conventional video reproduction apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Video reproduction apparatus, 11a, 11b ... DT head, 12 ... Video signal processing part, 13 ... DT head control part, 14 ... Reference signal generation part, 15 ... Substitute V pulse generation part, 16 ... ... reproduction V pulse missing detection part, 17 ... switching part, 50 ... magnetic tape

Claims (2)

In the video playback device that interpolates and plays back when the vertical synchronization pulse for playback of video information is missing,
Detecting a lack of the vertical synchronization pulse for reproduction of the video information, and counting a number of lacks, a vertical synchronization pulse missing detection unit;
An alternative vertical synchronization pulse generator for generating an alternative vertical synchronization pulse having a constant phase with respect to the reproduction reference signal;
When missing of the vertical sync pulse is detected and the number of missing does not reach a predetermined number, the dynamic tracking head control unit uses the vertical sync pulse as a reference and the head according to the head height during variable speed reproduction. The vertical synchronization pulse predicted by counting the horizontal synchronization signal in consideration of the fluctuation width of the vertical synchronization pulse is used for reproducing the video information, and when the number of missing parts reaches a predetermined number, the predicted vertical synchronization A switching unit for switching to use the alternative vertical synchronization pulse for reproduction of the video information instead of a pulse;
A video playback apparatus comprising: 2. The video reproduction apparatus according to claim 1, wherein the reproduction reference signal is a head switching pulse for switching a head for reproducing the video information recorded on the magnetic tape.

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