JP3163834B2 - Digital signal recording / reproducing method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for recording and reproducing digital signals, and more particularly, to a method and apparatus for recording and reproducing digital signals having a low bit rate such as video telephone signals.

[0002]

2. Description of the Related Art Hitherto, as a videophone device using ISDN, for example, "Communication and New Media", written by Naohiko Kamae, pp. 147-143. 69-80, Jan. 30, 1992, issued by Maruzen Co., Ltd.

The video telephone shown here has a configuration as shown in FIG. 3, and the format of data used in the video telephone is configured as shown in FIG.

[0004] A conventional videophone device will be described with reference to FIGS. 3 and 4.

In FIG. 3, an image centered on the user's face captured by the television camera 1 is converted into an analog component video signal, and the video codec 5
Supplied to Further, the voice spoken by the user is converted into an audio signal by the microphone 3 and supplied to the audio codec 6.

[0006] The video codec 5 is, for example, a CCIT.
Recommendation T. H. H.261, and A / D conversion, motion compensation inter-frame prediction, DCT (discrete cosine transform),
Performs quantization and compression processing by variable-length coding.
As shown in FIG. 4, the parity is added and supplied to the transmission control unit 7. The audio codec 6 is, for example, a CCITT Recommendation G. 711 or G. The audio signal supplied from the microphone 3 is converted into a digital signal (in the case of G.722, data compression is also performed), and a parity is added as shown in FIG. Supply to the control unit 7.

[0007] The transmission control unit 7 is, for example, a CCITT recommendation H.264. 221 and is compatible with video codec 5
A header is added to each of the parity-added video data supplied from the A / D converter and the parity-added audio data supplied from the audio codec 6 to form the block shown in FIG. A videophone signal obtained by time-division multiplexing a block of data is transmitted to the
The data is transmitted to the ISDN line 9 having a transmission bit rate of 382 kbit / sec.

[0008] The videophone signal transmitted from the communicating party to the ISDN line 9 is supplied to the transmission control unit 7 via the line interface 8. The transmission control unit 7 separates video data and audio data with parity from the video telephone signal supplied from the line interface 8, and supplies the video data to the video codec 5 and the audio data to the audio codec 6.

The video codec 5 performs processing such as error correction processing, decoding of a variable length code, inverse quantization, inverse DCT, and D / A conversion on the video data supplied from the transmission control unit 7, and performs analog processing. It is converted to a component video signal and output to the monitor 2. Further, the audio codec 6 performs processing such as error correction processing and D / A conversion on the audio data supplied from the transmission control unit 7 and outputs the data to the speaker 4.

A rotating head forms an oblique track on a magnetic tape wound on a rotating drum, and records and reproduces video data or audio data in a divided area on the track in a time-division manner. Digital VTRs have been proposed.

FIG. 5 is a block diagram showing an example of the configuration of such a digital VTR. 5, the recording processing circuit 21, the luminance signal Y which constitutes the analog component video signal, the color difference signals P _R, is P _B are input. Each of these signals is subjected to A / D conversion, blocking, shuffling, DCT (discrete cosine transform), quantization and compression by variable length coding, and framing, and is supplied to the parity generation circuit 22. .

The data supplied to the parity generation circuit 22 is added with a parity of a product code structure, and then supplied to a sync (SYNC) and ID generation circuit 23, where a synchronization code and an ID are added. Then, parallel / serial conversion and conversion into a recording code are performed by the channel encoder 24, amplified by the amplifier 25, supplied to the magnetic head 27 via the recording side terminal R of the switching circuit 26, and placed on the magnetic tape 28. Be recorded. Here, there are a plurality of video data for one frame, for example, 10 in the NTSC system, 12 in the PAL system, and 2 in the HDTV system.
It is recorded as zero oblique tracks.

Although not shown here, audio data, subcodes and ATF pilot signals are supplied to a channel encoder 24 and the magnetic head 2
7, the video data is recorded in a divided area of each track on the magnetic tape 28 in a time-division manner.

At the time of reproduction, data reproduced from the magnetic tape 28 by the magnetic head 27 is transmitted to the switching circuit 26.
Is supplied to an amplifier and an equalizer 29 through a reproduction side terminal P, amplification and frequency characteristics are corrected, a recording code is decoded and a serial / parallel conversion is performed by a channel decoder 30, and a sync and ID detection circuit 31 is provided. Supplied to Then, the sync code and ID are detected by the sync / ID detection circuit 31 and supplied to the TBC 32 together with the reproduced data. The data supplied to the TBC 32 is subjected to time-axis fluctuation removal, and then subjected to an error correction process using a product code by the ECC circuit 33, and then supplied to the reproduction processing circuit 34.

The video data supplied to the reproduction processing circuit 34 is subjected to deframing, decoding of a variable length code, inverse quantization,
Conversely DCT, deshuffling, and the process of the deblocking is applied, is further converted into an analog component video signal, the luminance signal Y, the color difference signals P _R, is output as P _B.

Although not shown here, EC
The audio data and subcode output from the C circuit 33 are processed in the same manner. The channel decoder 30
The ATF pilot signal is separated from the output of, and supplied to the ATF circuit to perform tracking correction.

FIG. 6 is a diagram showing an example of the track format of the digital VTR configured as described above.
In this figure, the left end of the track is the head entrance (entry)
The right end of the track is the head exit (separation) side. Further, no data is recorded in the margins 1 and 2 and the IBG (inter-block gap), which are hatched areas. The T (track) -amble area added before the first ATF area (ATF1) and the amble area (preamble or postamble) added at both ends of the data recording area include, for example, the bit frequency of the recording data and A pulse signal having the same frequency is recorded and used for locking a PLL provided on the reproducing side for bit clock extraction. The margins 1 and 2 provided at both ends of the track correspond to the case where the track formation position changes due to jitter. The IBG is an area for securing a post-recording margin.

A first ATF area (ATF1) in which a pilot signal for ATF and a timing sync for post-recording are recorded adjacent to margins 1 and 2, and a second ATF
An area (ATF2) is provided. And the first AT
A recording area for audio data, a recording area for video data, a recording area for subcode, and a second ATF area are provided in this order from the F area in the scanning direction of the head. In the subcode recording area, data such as a high-speed search index and a time code are recorded. The number indicating the length of each area is the number of bytes.

FIG. 7 is a diagram showing an example of a format of one sync block and framing of video data and audio data. Here, the number is the number of bytes.

FIG. 7A is a diagram showing a data format of one sync block, in which 78 bytes of video data or audio data are added later with 8 bytes of horizontal parity, and 2 bytes of synchronization code are added before. And a 3-byte ID. The ID has information for identifying the sync block number and the type of data. Next, a method of forming the sync block will be briefly described.

FIG. 7B shows a framing format of video data. In this figure, the recording processing circuit 1 vertically arranges 45 video data (including 2 bytes of quantization information and the like) of 78 bytes in the horizontal direction.
The parity generator 22 adds the horizontal parity C1 and the vertical parity C2, and the sync (SYNC) and ID generator 23 adds a synchronization code and an ID. Then, parallel / serial conversion is performed by the channel encoder 24, and the data is recorded for each sync block in FIG. FIG.
Three frames (b) are video data for one track.

FIG. 7C is a diagram showing a framing format of audio data. One frame is audio data for one track.

As is apparent from FIGS. 6 and 7, the recording bit rate of NTSC video data in this digital VTR is about 25 Mbit / sec.

[0024]

When recording a video telephone signal received by a video telephone apparatus configured as shown in FIG. 3 on a digital VTR configured as shown in FIG. 5, the video signal is It is considered that an analog component video signal output from the video codec 5 of the videophone device is input to the recording processing circuit 21 of the digital VTR. Similarly, for an audio signal, an analog audio signal output from the audio codec 6 of the videophone device is converted to a digital VT signal.
It is conceivable that the signal is input to R, converted into a digital audio signal and recorded.

In such a configuration, since the data amounts of video data and audio data are expanded, converted into analog signals, then converted into digital signals again, and the data amount is compressed, there is no waste in processing. And the quality of the video and audio signals may be degraded.

When outputting the reproduction data of the digital VTR to the videophone device, the output of the reproduction processing circuit 34 is input to the video codec 6, which has the same problem.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and records without compressing the data amount of a digital signal having a bit rate lower than the recording rate of a digital signal recording and reproducing apparatus. It is another object of the present invention to provide a digital signal recording / reproducing method and apparatus capable of transmitting a reproduced digital signal without expanding the data amount.

[0028]

SUMMARY OF THE INVENTION In order to solve the above technical problems, the present invention converts an analog signal into a first digital signal having a compressed data amount, and records and reproduces the data in a predetermined data format. In a method of recording and reproducing a second digital signal having a lower bit rate than the recording bit rate of the digital signal recording / reproducing apparatus by using the digital signal recording / reproducing apparatus, the bit rate of the second digital signal is set to The bit rate of the digital signal reproduced at the intermittent time is converted into the bit rate of the second digital signal while recording at the intermittent time in a predetermined data format so as to conform to the recording bit rate of the apparatus.

Further, according to the present invention, in a digital signal recording / reproducing apparatus, first means for converting an analog signal into a first digital signal having a compressed data amount, and increasing the bit rate of the second digital signal. A second means;
A third means for selecting the output of the first means or the output of the second means, recording and reproducing in a predetermined data format, and recording and reproducing the output of the second means at an intermittent time; A fourth means for expanding the data amount of the digital signal obtained by recording and reproducing the output of the first means and converting the data amount into an analog signal; and a fourth means for lowering the bit rate of the digital signal obtained by recording and reproducing the output of the second means. 5 means.

In the present invention, the second digital signal is, for example, video data and audio data received by the video telephone, output data of a computer, and the like.

[0031]

The present invention uses a digital signal recording / reproducing apparatus for converting an analog signal into a first digital signal having a compressed data amount and recording / reproducing the data at an intermittent time in a predetermined data format. The bit rate of the second digital signal having such a low bit rate is adapted to the recording bit rate of the digital signal recording / reproducing apparatus, and recording / reproducing is performed in a predetermined data format. Then, the bit rate of the reproduced digital signal is converted to the bit rate of the second digital signal.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing a digital signal recording / reproducing apparatus according to the present invention. Here, parts corresponding to those in FIG. 5 described above are denoted by the same reference numerals.

This digital signal recording / reproducing apparatus is obtained by adding an interface section 10 to a transmission control section 7 of a video telephone apparatus to a conventional digital VTR. The transmission control unit 7 separates video data and audio data to which parity has been added from the videophone signal received via the line interface 8 and supplies the video data and the audio data to the first memory 10 a of the interface unit 10. The transmission control unit 7
Sends information identifying the type of data to the interface unit 1
0 to the controller 10c, and further inputs the data supplied from the second memory 10b of the interface unit 10. The controller 10c includes a first memory 10
a and control of writing / reading of the second memory 10b and supply of various control signals to a system control microcomputer (not shown, hereinafter referred to as a syscon) of the digital signal recording / reproducing apparatus.

The recording bit rate of the NTSC video signal in the digital signal recording / reproducing apparatus according to the present invention is about 25, similar to the above-mentioned conventional digital VTR.
Mbit / sec. When this is converted into one track, it becomes about 80 kbit. Therefore, if the transmission bit rate of the videophone device is 384 kbit / sec, 384 kbit, which is data received per second,
5 tracks is enough to record.

Therefore, according to the present invention, the videophone device is 2
The data received per second is recorded and reproduced using 10 tracks. For this purpose, the video data and the audio data to which the parity is added supplied from the transmission control unit 7 are stored in the first memory 10a of the interface unit 10.
And time compression to about (1/60). As a result, 2
The video data and audio data for one second are time-compressed to about 1/30 second, and accordingly, the bit rate becomes about 38
It is converted from 4 kbit / sec to about 25 Mbit / sec. FIGS. 2A to 2D show this state. The video data and audio data whose bit rates have been converted in this way are supplied to the parity generation circuit 22 via the switching circuit 35. The selection of the terminal in the switching circuit 35 is configured so that the controller 10c supplies a control signal for instructing switching to the system controller.

The video data and the audio data supplied to the parity generation circuit 22 are converted to a conventional digital VTR.
Similarly to the above, the parity of the product code configuration is added here, and then supplied to the sync and ID generation circuit 23, where the synchronization code and the I
D is added. At this time, based on information for identifying the type of data supplied from the controller 10c of the interface unit 10 to the system controller, the sync and ID generation circuit 23
, Information for identifying the type of data is added to the ID. Then, parallel / serial conversion and conversion into a recording code are performed by the channel encoder 24, amplified by the amplifier 25, supplied to the magnetic head 27 via the recording side terminal R of the switching circuit 26, and placed on the magnetic tape 28. Be recorded. Both video data and audio data constituting the videophone signal are recorded in the video data recording area of FIG. 6 in a time-division manner.

As shown in FIG. 2 (d), the video data and the audio data are output every 1 second.
Since the intermittent signal is a frame period (1/30 second), the magnetic tape 28 is moved for one frame every two seconds, ie, 10 frames.
Only the truck runs intermittently. This control is performed by the system controller.

At the time of reproduction, the magnetic tape 28 is run intermittently by one frame every two seconds, that is, by ten tracks. The data reproduced from the magnetic tape 28 is ECC
The processing up to the supply to the circuit 33 is basically the same as that of the conventional digital VTR. The data output from the ECC circuit 33 is supplied to the interface unit 10 via the switching circuit 36. The selection of the terminal in the switching circuit 36 is performed by the controller 10 as in the case of recording.
c may supply a control signal for instructing switching to the system controller. However, recording identification data in a subcode area or an ATF area, and reproducing and switching the identification data. Can also.

The video data and audio data input to the interface unit 10 are time-expanded by a factor of about 60 by the second memory 10b and supplied to the transmission control unit 7. The video data and the audio data supplied to the transmission control unit 7 are supplied to the monitor 2 and the speaker 4 via the video codec 5 and the audio codec 6, respectively.

In the above description, the video data and audio data with parity supplied from the transmission control unit 7 are
Although the video data is recorded in the video data recording area shown in FIG. 6, error correction may be performed in the interface unit 10 using the parity, and the error-corrected video data and audio data may be recorded. .

The sum of the IBG and the amble between the video data recording area and the audio data recording area is calculated by multiplying the sum of the data sync block length (91 bytes in the above embodiment) by 182 bytes (for example, twice as large as 182 bytes). ), And video data or audio data may be continuously recorded in this portion.

Further, it is also possible to transmit video data and audio data for answering machine recorded in advance on the magnetic tape 28 to the communication partner.

Further, when the bit rate of the videophone signal is low, for example, 64 kbit / sec, the received signal for one second can be recorded on one track. Then 1
What is necessary is just to control the writing / reading of the first memory 10c and the running of the magnetic tape 28 so as to record on the zero track.

The bit rate is, for example, 10 Mbit / s
If the value is high, such as ec, the data received by the videophone device is time-compressed to about 1/2, and control is performed so that the same data is repeatedly recorded twice for every five tracks while the magnetic tape is continuously running. As described above, when the same data is repeatedly recorded, error correction during reproduction is facilitated.
Of course, in this case, it is not necessary to repeatedly record the same data, and conversely, the bit rate is 384 kbit / sec.
Or 64 kbit / sec, the same data may be repeatedly recorded two or more times.

The video telephone apparatus is a model capable of communicating in a plurality of different communication modes (transmission bit rate, coding scheme, etc.), and the transmission control unit 7 is, for example, a CCITT Recommendation H.264. 2
When the communication mode is determined by performing negotiation with the partner terminal according to the procedure based on the C.42 standard,
The transmission control unit 7 transmits the communication mode information to the interface unit 10
If the controller 10c is configured to transfer this information to the system controller of the digital signal recording / reproducing apparatus, the recording / reproducing operation can be automatically controlled according to the communication mode.

In the present invention, the digital signal recording / reproducing apparatus may be constituted as a video telephone signal recording / reproducing apparatus. In this case, the recording processing circuit and the reproduction processing circuit become unnecessary, so that the hardware can be reduced.

[0048]

As described above, according to the present invention, the data amount of digital data having a low bit rate, such as a videophone signal, can be recorded and reproduced without being compressed and decompressed. And the signal quality can be prevented from deteriorating.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a digital signal recording / reproducing apparatus according to the present invention.

FIG. 2 is a timing chart showing an operation of an interface unit constituting the digital signal recording / reproducing apparatus according to the present invention.

FIG. 3 is a block diagram showing a simplified configuration of a conventional videophone device.

FIG. 4 is a diagram showing a data format of a videophone signal.

FIG. 5 is a block diagram showing an example of a configuration of a conventional digital VTR.

FIG. 6 is a diagram showing an example of a track format of a conventional digital VTR.

FIG. 7 is a diagram showing an example of one sync block and framing format of video data and audio data in a conventional digital VTR.

[Explanation of symbols]

10 interface section, 21 recording processing circuit, 3
4 Reproduction processing circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 20/10 H04N 5/92

Claims (4)

(57) [Claims] 1. A digital signal recording / reproducing apparatus which converts an analog signal into a first digital signal having a reduced data amount and records / reproduces the data in a predetermined data format, using a recording bit rate of said digital signal recording / reproducing apparatus. A method of recording and reproducing a second digital signal having a lower bit rate, wherein the bit rate of the second digital signal is adapted to a recording bit rate of the digital signal recording and reproducing apparatus.
A digital signal recording / reproducing method, wherein the recording is performed at the intermittent time in the predetermined data format, and the bit rate of the digital signal reproduced at the intermittent time is converted into the bit rate of the second digital signal. 2. The digital signal recording / reproducing method according to claim 1, wherein the second digital signal is video data and audio data received by the video telephone. 3. A first means for converting an analog signal into a first digital signal having a reduced data amount; a second means for increasing a bit rate of a second digital signal; and the first means. Or the output of the second means,
Recording and reproducing in a predetermined data format , and
A third means for recording and reproducing at an intermittent time when recording and reproducing the output of the means, and an analog signal by expanding the data amount of the digital signal obtained by recording and reproducing the output of the first means. A digital signal recording / reproducing apparatus comprising: a fourth means for converting; and a fifth means for lowering a bit rate of a digital signal obtained by recording and reproducing an output of the second means. 4. The digital signal recording / reproducing apparatus according to claim 3, wherein the second digital signal is video data and audio data received by the video telephone.