KR0131963B1 - Time compression video on demand for video cassette recorder - Google Patents

Abstract

A VCR(video cassette recorder) used in a VOD(video on demand) is disclosed. The VCR comprises a system controller(30) for outputting a control signal to control the VCR; a channel encoder(10), responsive to the control signal, for adding an error correcting signal to a bit stream encoded with MPEG1 to modulate the added signal; a first buffer(20), responsive to the control signal, for buffering the output from the channel encoder(10); a servo unit(60), responsive to the control signal, for converting the traveling speed of the video tape; a unit(40) for writing the output from the first buffer(20) at the video tape through a head and for reading the signal recorded at the video tape; a channel decoder(50) for decoding the output signal from the unit(40); a second buffer(70), responsive to the control signal, for buffering the output signal from the channel decoder; and an audio/video decoder(80) for receiving the output signal from the second buffer to decode it.

Description

Video cassette recorder for video compression on demand

1 is a block diagram of a video cassette recorder for video compression on demand video according to the present invention.

2 shows a format of a signal recorded on a video tape of a video cassette recorder for a time compression on-demand video cassette according to the present invention.

3 is a, b is a schematic diagram showing a state in which the head is mounted on the head drum in the video cassette recorder for time compression on-demand video according to the present invention.

4 is a view showing a state in which a signal of a video tape is read in a special playback mode of a video compression recorder for a time compression on-demand video cassette according to the present invention.

* Explanation of symbols for main parts of the drawings

10: channel encoder 20: buffer

30: system control circuit 40: recording and reading circuit

50: channel decoder 60: servo unit

70: buffer 80: audio / video decoder

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital video cassette recorder, and more particularly, to a video cassette recorder for a time compression on-demand video that can record a video signal input by time compression on a magnetic tape as it is, and decompress and reproduce the compressed video signal.

Video signal transmission and storage is evolving into an All Digital transmission system. Among them, digital VCRs, which are recognized as next-generation home appliances, are required to be developed due to the advantages of high quality and multifunction.

One of these digital VCRs, a VCR for Time Compressed Video On Demand, is currently being studied. Time Compression Video for video on demand, as well as data compression, is recorded on video tape by time compression so that subscribers can receive a movie in a short time, record it on video tape, and play it back for viewing. Therefore, in the home, communication network fees can be greatly saved by receiving video signals in a short time and recording them on video tapes.

However, VCRs used for such time compression video on demand are not currently developed.

SUMMARY OF THE INVENTION The present invention has been made in view of this point, and an object of the present invention is to provide a VCR for time compression video for video that is suitable for time compression video on demand.

It is another object of the present invention to provide a VCR for time compression video having an appropriate track format for recording a video signal on a magnetic tape in a VCR for time compression video.

It is still another object of the present invention to provide a VCR for a video compression video having a structure of a video head drum capable of reading out a signal recorded on a magnetic tape in a playback mode of a VCR for video compression for video.

A feature of the present invention for achieving this object is a VCR for video compression on-demand video, comprising: a system control circuit for outputting a control signal for controlling the VCR; A channel encoder for adding an error correction signal to a digital signal in the form of a bit stream encoded according to a control signal in accordance with a control signal, and outputting the NRZ modulated signal; A first buffer buffering an output of the channel encoder according to the control signal; A servo unit for driving in accordance with a control signal to convert a video tape traveling speed; A recording and reading circuit for recording the output of the first buffer to the video tape through a head, and reading and outputting the signal recorded on the magnetic tape at 1/6 speed at the time of recording; A channel decoder for performing an NRZ decoding on the signal applied from the recording and reading circuit and analyzing the error correction signal to remove the error; Second buffering to control buffer the output of the channel decoder; A video compression video VCR having an audio / video decoder that receives the output of the second buffer and decodes the image by MPEG 1 scheme and processes the image and audio.

Another aspect of the invention is a method of recording a signal on a magnetic tape in a VCR for time compression video on demand, comprising the steps of: recording a 1300-bit full-text signal; Sequentially recording a 20-bit sync signal, a 30-bit ID signal, a 770-bit video and audio signal, and an 80-bit internal parity signal over 125 times; Sequentially recording a synchronization signal of 20 bits, an ID signal of 30 bits, an external parity signal of 770 bits, and an internal parity signal of 80 bits over 11 times; There is a VCR for video compression on-demand that performs the step of recording a 1300 bit back gate signal.

Another feature of the invention is that the first and second heads for reproduction and recording which face each other, and the third and fourth heads for reproduction which face and face each other with the first and second heads at a predetermined angle to each other. In the VCR for video compression on-demand video, any one of the third and fourth head is formed at a position having a predetermined step with the first and second head, respectively. It's in a video VCR.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of a VCR for time compression video on demand according to the present invention, in which a digital signal in the form of a bit stream is applied to the channel encoder 10. At this time, the digital signals applied to the channel encoder 10 are video and audio signals encoded in MPEG-1 format.

The channel encoder 10 is configured to add an error correction signal to a digital signal in the form of a bit stream encoded according to the MPEG 1 method according to a control signal applied from the system control circuit 30, and NRZ modulate and output the signal.

2 shows the format of the digital signal output from the channel encoder 10. As shown, the channel encoder 10 includes a 130-bit preamble signal, a 20-bit synchronization signal, a 30-bit identification signal, a 770-bit MPEG-1 video and audio signal, It outputs 80 bits of internal parity signal over 125 times, and outputs 20 bits of synchronization signal, 30 bits of identification (Identification), 770 bits of external parity signal, and 80 bits of internal parity signal over 11 times. . Thereafter, the channel encoder 10 is configured to sequentially output 1300 bits of postamble.

The buffer 20 connected to the channel encoder 10 buffers and outputs an output signal of the channel encoder 10 under the control of the system control circuit 30, and the write and read circuit 40 buffers the buffer 20. The output of the data is recorded on the magnetic tape through the head, and the signal recorded on the magnetic tape is read and applied to the channel decoder 50.

At this time, the signal recorded on the magnetic tape will be recorded in the format as shown in FIG.

On the other hand, the servo unit 60 changes the traveling speed of the magnetic tape recorded and read by the head under the control of the system control circuit 30. That is, the servo unit 60 runs the magnetic tape at a speed of 33.35 mm per second in the recording mode for recording signals on the magnetic tape, but 0.556 per 1/10 second of the magnetic tape in the reproducing mode for reading signals recorded on the magnetic tape. Intermittent running at the speed of mm.

Therefore, the transmitted video and audio signals can be transmitted six times faster than the signals read from the magnetic tape, and by reading the signals transmitted and recorded on the magnetic tape at 1/6 speed, the user can Video and audio signals can be reproduced and viewed at their original image speed.

That is, the channel decoder 50 NRZ decodes the signal read out at the 1/16 speed of the speed recorded on the magnetic tape, analyzes the error correction signal, removes the error, and decodes the original MPEG 1 signal. .

As described above, the buffer 70 that receives the decoded signal as the MPEG 1 signal is buffered and output under the control of the system control circuit 30, and the audio / video decoder 80 receives the MPEG 1 signal. Decode and process the original audio and video signals and apply them to the speakers and monitor.

Therefore, in the present invention, the audio and video signals can be transmitted and received at a speed six times the speed at which the signal is read and reproduced by the head, thereby recording on the magnetic tape.

If a separate head is not used because of a tape speed difference at the time of reproduction, tracking deviation occurs and the error rate of the reproduction signal is increased.

In the conventional two-head method, the video signal recorded on the video tape is not completely read by the difference between the azmus angle of the head and the azimuth angle of the video tape during special playback. In order to overcome the disadvantages of the two-head method, the proposed method is a four-head method. In this method, a playback-only head is added in close proximity to two conventional heads to match the azimuth angle of the video tape with the azimuth angle of the playback-only head, thereby reading out the video signal recorded on the video tape in a special mode. come. However, even in such a four-head method, since a portion where the azimuth angle between the video tape and the heads does not match is generated, there is a problem in that image quality deteriorates.

The present inventor has proposed a head having a structure as shown in (a) and (b) of FIG. 3 to solve this problem.

As shown in (a) of FIG. 3, the head drum HD includes two reproduction heads HR1 and HL1 symmetrically with each other, and the heads HR and HL have an angle of 41.3 degrees. And regeneration heads HR2 and HL2.

At this time, the heads HR1 and HL1 have a width of 40 μm as shown in FIG. 2B, and the heads HR2 and HL2 have a width of 58 μm. At this time, the reproducing head head HL2 and the heads HR1, HL1, HR2 have a step of 29 um and are mounted on the drum HD. This is the case when the track width of the tape is 29um, and if the track width is changed, this value will be changed.

4 shows the trajectory of the heads HL1, HR1, HR2, and HL2 of this configuration traveling the track of the video tape T in the still mode.

The tracks indicated by the symbols R and L in the illustrated tape T mean tracks whose azimuth angles with the heads HR1, HR2 and HL1, HL2 are respectively matched. At this time, the track width is 29um.

In this state, when the VCR is operating in the playback mode, the head HR1 will start to contact the tape at position a and travel along the dotted line A1. At this time, the head HL2 is brought into contact with the tape at the position b by the step. That is, the head HR1 and the head HL2 are placed at the tape T positions a and b at the same time by the step of the head HL2.

In this state, the signal of the tape read by the head HR1 will be the portion c by the azimuth angle. That is, in the present invention, it can be seen that the signal recorded in the part d is read simultaneously in addition to the signal recorded in the part c.

In other words, the present invention can obtain accurate data without any output loss in the playback mode by forming a height difference corresponding to the track width of the remaining heads and the tape in any one head for playback in a 4-head digital VCR. .

As described above, the present invention processes video and audio signals input as MPEG 1 digital signals, records them on a video tape at high speed, and reproduces them at a speed of 1/6 at the recorded speed. Receiving and recording on video tape can significantly reduce the network usage fee.

In addition, the present invention has the effect of obtaining accurate data by forming any one of the reproducing heads with a step.

Claims (3)

A video cassette recorder for time compression video on demand, comprising: a system control circuit for outputting a control signal for controlling the video cassette recorder; A channel encoder for adding an error correction signal to a digital signal in the form of a bit stream encoded according to a control signal in accordance with a control signal, and performing NRZ modulation on the digital signal; A first buffer buffering an output of the channel encoder according to the control signal; A servo unit for driving in accordance with a control signal to convert a video tape traveling speed; A recording and reading circuit for recording the output of the first buffer to the video tape through a head, and reading and outputting the signal recorded on the magnetic tape at 1/6 speed at the time of recording; A channel decoder which NRZ decodes the signals applied from the recording and reading circuits and then removes the errors under an error correction signal; A second buffering buffering an output of the channel decoder according to a control signal; And an audio / video decoder configured to receive the output of the second buffer, decode the video signal in an MPEG 1 scheme, and output the video and audio. CLAIMS What is claimed is: 1. A method of recording a signal on a magnetic tape in a video cassette recorder for time compression video on demand, comprising: recording a 1300-bit full signal; Sequentially recording a 20-bit synchronization signal, a 30-bit ID signal, a 770-bit audio signal, and an 80-bit internal parity signal over 125 times; Sequentially recording a synchronization signal of 20 bits, an ID signal of 30 bits, a video and external parity signal of 770 bits, and an internal parity signal of 80 bits over 11 times; A video cassette recorder for time-compressed video that performs the step of recording a 1300-bit back-signal. A time compressed video-on-demand video having first and second heads for reproduction and recording facing each other, and third and fourth heads for reproduction and facing each other at a predetermined angle with the first and second heads. The cassette recorder of claim 1, wherein one of the third and fourth heads is formed at a position having a predetermined step with the first and second heads.