Method and Apparatus for Recording and Playing Back Monitored Video Data

Abstract

A method and an apparatus are provided for recording and playing back monitored video data for recording monitored video data generated continuously for a long time on a magnetic tape. Video signals from a video camera are converted to digital signals in an A / D converter, compressed and encoded in a compression encoder and decoder circuit, then transferred to a time axis compression circuit which includes a first memory, the second memory, an SCSI controller, and a hard disk unit. The digital signal is thereafter compressed on the time axis and recorded on the magnetic tape loaded in a D-VHS standard VTR via an I / F circuit.

Description

BACKGROUND OF THE INVENTION [0001] The present invention relates to methods and apparatuses for recording and playing back video data, more particularly to a method and an apparatus for recording and playing back monitored video data, which will be suitable for recording video data for a long time for the purpose of monitoring and preventing of crimes.[0002] There is provided a prior art time lapse VTR used as a video data recording device for recording video data from a video camera, suitable for monitoring and preventing crimes. Many of this type VTR are improved from a home VHS VTR which is very popular at present to enable a long time recording. For example, in such a time lapse VTR, the magnetic tape can be fed at a ⅓ speed of the VHS Extended Play (EP) mode to record only one of the input video 3 fields on the tape, so that the recording time can be extended to 3 times that of the EP mode. Consequently, when a 120-min tape is used, the recording time is extended to 6 hours (12...

AI Technical Summary

Benefits of technology

[0009] It is an object of the present invention to provide a method and an apparatus for recording and playing back monitored video data, which can store video data on a magnetic tape for a period enough to be used for monitoring and preventing crimes, etc. In addition, in the apparatus, it is no need to record video data while the recording head is put in contact with the magnetic tape for a long time and while the recording head is moved, without special mechanisms for intermittent feeding, etc. In other words, a general home VTR can also be used to store video data on a magnetic tape for a period enough to monitor and prevent crimes, etc.

[0010] It is another object of the present invention to solve the above-mentioned problems of conventional time lapse VTR and provide an apparatus for recording and playing back video data, which can improve its mechanical reliability and extend the life of the magnetic tape in use by reducing the operating time of the parts that will apt to wear and be damaged, without employing any high precision control means for intermittent tape feeding.

[0011] It is a further object of the present invention to provide an apparatus for recording and playing back video data, which can output good quality playback images without degrading the playback signals even in a different tape-speed mode from the recording mode.

[0014] Furthermore, the present invention provides an apparatus for recording and playing back monitored video data and storing video signals generated continuously for a long time on a magnetic tape, comprising a means of generating video signals continuously for a long time; a means of entering video signals generated by the video signal generating means continuously for a long time and compressing the video signals on the time axis so as to be output as digital signal video data; and a means of recording and playing back digital video data from the time axis compressing means on a magnetic tape, wherein the period in which the magnetic tape recording means records digital video data on the magnetic tape is shorter than the period in which the video signal generating means generates video signals continuously.

Problems solved by technology

This system can have the maximum recording time of, for example 720 hours using a normal 120-min tape by, recording video data at a rate of 1 field per 2 seconds (120 fields) per frame (2 hours×3 times×120=720 hours) In such a super-long time recording operation, the average tape feed speed is very slow, so that it becomes difficult to control the continuous feeding of the tape.

To avoid this problem, the tape is fed intermittently in most cases and accordingly, it becomes impossible to record audio signals in audio tracks.

Further, since the cylinder has a large moment and takes much time until its rotation speed is stabilized, the cylinder must be rotated almost at a fixed speed continuously during the recording.

Especially, in the above super-long recording mode (720-hour mode), the VTR has a disadvantage that because the cylinder is kept rotated in contact with the tape for 720 hours, the tape is damaged far more rapidly than used for a home VTR.

In the same way, because the head is in contact with the tape, the head is also worn rapidly.

The mechanisms such as the motor and belt used for making the cylinder rotate are also degraded rapidly and often damaged, since they are running for a long time respectively.

Further, conventional helical scanning VTR also has a following defect; the recording track pattern angle on the tape loaded is decided by both the rotation speed of the cylinder and the feed speed of the tape, so that the track pattern recorded at the above slow speed tape feeding or the tape stops has an angle different from the normal speed tape feeding.

Therefore, when playing back the track pattern recorded in such way, a mismatching occurs between the tracing angle of the head and the angle of the track pattern, causing the S / N (signal-noise ratio) to be degraded in a part of the playback signals, with the resultant of lowering the quality of output pictures significantly.

Images