Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Reexamination Certificate
1998-09-08
2001-05-15
Nguyen, Huy (Department: 2615)
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
C386S349000
Reexamination Certificate
active
06233391
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to video recorders for use with a magnetic tape or similar recording medium for intermittently recording thereon video signals obtained from a monitoring TV camera installed, for example, at the entrance of a bank, commodity store or house.
2. Description of the Related Art
Generally with video recorders of the helical scan type, the signal bearing surface of a magnetic tape running in one direction is traced in an oblique direction with a magnetic head to record a series of video signals on a plurality of tracks thereby formed on the signal bearing surface. Since the video recorder connected to a monitoring TV camera records video signals on a magnetic tape of given length over a long period of time, the video signals obtained by the camera are recorded “intermittently,” i.e., as thinned out in a predetermined cycle, on the magnetic tape.
For intermittent recording, digital video recorders can be used which are adapted to digitize the analog video signals obtained by a TV camera and record the digital signals on a magnetic tape.
FIG. 6
shows a processing example wherein digital video signals which are sequential in time are intermittently recorded on a magnetic tape to obtain a recording time twice the real time. In the case where items of time series data
1
,
2
,
3
,
4
, . . . are input which are obtained by dividing a series of digital video signals into frames or groups each comprising a plurality of frames as shown in FIG.
6
(
a
) , these items of input data are recorded on the magnetic tape, with every other data unit thinned out with a cycle T as shown in FIG.
6
(
c
)
In this case, the magnetic tape repeats running and stopping alternating in a cycle of T/2 as shown in FIG.
6
(
b
) to record images during running.
In this intermittent recording operation, however, the running and stopping of the magnetic tape alternate in repetition with a cycle shorter than the cycle T of intermittent recording, so that the tape fails to travel with stability every time. Consequently, the head traces the tape at an angle different from the head trace angle of the normal recording operation.
Accordingly, playback of the magnetic tape used for intermittent recording requires a complex procedure such as altering the head trace angle in conformity with the head trace angle used for recording. Especially in the case of digital video recorders, normal reproduction of images requires accurate reproduction of data permitting correction of errors, whereas if head tracing involves an angular deviation in playing back the magnetic tape used for intermittent recording, there arises a problem in that the recorded data can not be read from the tape accurately, failing to afford a normal reproduction.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a digital video recorder which is capable of intermittently recording digital video signals at an accurate head trace angle.
The present invention provides a digital video recorder including a signal recording system comprising:
memory means capable of storing therein digital video signals available over a period of time longer than the cycle of intermittent recording;
writing control means for extracting digital video signals for one or a plurality of frames with the cycle of intermitting recording and writing the extracted digital video signals to the memory means during the extraction; and
recording control means for controlling reading of digital video signals from the memory means, running of a recording medium and recording of digital video signals on the recording medium, the recording control means being adapted to repeat the operations of causing the recording medium to start to run, reading digital video signals from the memory means and recording the read signals on the recording medium when a predetermined quantity of digital video signals have been written to the memory means, and bringing the recording medium to a stop and ceasing recording on the recording medium when the predetermined quantity of digital video signals have been read from the memory means.
With the digital video recorder of the present invention, the digital video signals extracted with the cycle of intermittent recording are written to the memory means to a predetermined capacity, thereafter read from the memory means and recorded on the recording medium, and these operations are repeated, so that the recording medium can be kept running while the signals are being read from the memory means. After the recording medium is brought to a stop when all the digital video signals in the memory means have been read therefrom, the recording medium can be held at a halt until the memory means is filled with digital video signals written thereto.
Because the memory means has a capacity to store therein digital video signals which are available over a period of time longer than the cycle of intermittent recording, the period of time during which the recording medium can be kept running or at a halt is sufficiently longer than the cycle of intermittent recording, in corresponding relation with the storage capacity of the memory means.
Accordingly, the recording medium is caused to run and stopped less frequently than in the conventional video recorder which is adapted for intermittent recording without using a memory means, consequently minimizing the deviation of the head during tracing due to unstable travel of the recording medium.
More specifically, the writing control means determines the cycle of intermittent recording in accordance with time data contained in an intermittent recording command to be input from outside.
This makes it possible to lengthen the recording time for the medium in a desired ratio.
As an embodiment of the invention, the digital video recorder further includes a signal reproduction system for causing the recording medium having digital video signals intermittently recorded thereon to run at the same speed as when recording the signals and reproducing the digital video signals from the recording medium.
The signal reproduction system comprises:
memory means capable of storing digital video signals therein, and
reproduction control means for controlling reproduction of digital video signals from the recording medium, running of the recording medium, and writing and reading of digital video signals to and from the memory means, the reproduction control means being adapted to repeat the operations of stopping the recording medium when a predetermined quantity of digital video signals have been written to the memory means, and causing the recording medium to run when the predetermined quantity of digital video signals have been read from the memory means, the reproduction control means being operable to output the digital video signals read from the memory means while repeating the operations.
The memory means of the signal recording system is usable as the memory means of this system in common.
While the recording medium is repeatedly run and stopped in the digital video recorder having the signal reproduction system, the digital video signals reproduced from the medium is written to the memory means to a predetermined capacity, and in the meantime, the digital video signals are read from the memory means at a given rate and output, so that the recording medium can be kept running during the period in which the signals are written to the memory means.
Accordingly, the recording medium is run and stopped less frequently than in the conventional video recorder which reproduces signals without using a memory means, consequently minimizing the deviation of the head during tracing due to unstable travel of the recording medium.
More specifically, the reproduction control means determines the rate of reading signals from the memory means in accordance with reproduction rate data contained in an intermittent reproduction command to be input from outside.
This realizes the desired reproduction rate.
Digital video signals can be intermittently recorded
Morikawa Shigekazu
Okutani Ayumu
Armstrong Westerman Hattori McLeland & Naughton LLP
Nguyen Huy
Sanyo Electric Co,. Ltd.
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