Recording and reproduction of variable-speed playback data using a specific area on each track of a recording medium

A recording method and apparatus and a reproducing apparatus for digital signals in which data produced by encoding video signals by MPEG system, can be directly recorded and reproduced pictures having a superior picture quality may be obtained on variable-speed reproduction. According to the recording method and apparatus, each track is divided into a first area and a second area. The input data is directly recorded in the first area, and sequentially variable-speed playback data is recorded in the second area of each track. These variable-speed playback data are data among the input data which is obtained on intra-picture recording and which is collected from plural regions divided from a full frame.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a method and apparatus for recording and an 
apparatus for reproducing digital video signals. More particularly, it 
relates to a method for recording digital video signals whereby data 
produced by encoding video signals by e.g., the so-called MPEG system can 
be directly recorded and reproduced pictures having a superior quality may 
be obtained due to variable-speed reproduction. 
2. Description of the Related Art 
Developments of a digital video tape recorder (digital VTR), in which video 
signals are converted into digital signals, discrete cosine transformed 
and variable length encoded by e.g., Huffman encoding by way of data 
compression, and in which the resulting digital video signals are recorded 
on a magnetic tape by a rotary head in accordance with an azimuth 
recording system, are currently proceeding. In such digital VTR, the mode 
of recording video signals of the current television system, such as the 
NTSC system, referred to herein as SD mode, or the mode of recording of 
the high-definition television signals (HDTV signals), referred to herein 
as the HD mode, may be set. 
In the SD mode, video signals are recorded after compression to digital 
video signals of approximately 25 Mbps, whereas, in the HD mode, HDTV 
signals are recorded after compression to digital video signals of 
approximately 50 Mbps. 
With the conventional digital VTR, it has been envisaged to record input 
digital video signals (input data) directly on a magnetic tape and to 
reproduce and directly output data recorded on the magnetic tape. This has 
an advantage in that, by adding the function of directly 
recording/reproducing digital video signals (data) to the conventional 
digital VTR, the necessity of temporarily decoding input digital video 
signals for reproducing e.g., HDTV signals and re-encoding the HDTV 
signals in accordance with a pre-set encoding system for recording on the 
magnetic tape may be eliminated, thus obviating additional hardware. 
Specifically, if the digital VTR is fed with digital video signals obtained 
on encoding video signals in accordance with the MPEG system, that is a 
moving picture encoding system standardized in the Work Group (WG) 11 of 
the Sub-Committee of Joint Technical Committee (JTC) of the International 
Standardization Organization (ISO) and International Electric Committee 
(IEC), or with digital video signals reproduced from an optical disc, it 
is very convenient if the digital VTR has the function of directly 
recording/reproducing these digital video signals. 
The Advanced Television system (ATV system), which is a digital 
broadcasting employing the above MPEG system as the encoding system, is 
now explained. FIG. 12 shows, in a block diagram, the construction of the 
transmission system of the ATV system. In FIG. 12, the numerals 101 and 
102 denote a video compression encoder and an audio encoder, respectively. 
Video signals of the HDTV system are fed via an input terminal 103 to the 
video compression encoder 101, while audio signals are fed from an input 
terminal 104. 
The video compression encoder 101 encodes the input HDTV signals in 
accordance with the MPEG system for data compression. Thus the video 
compression encoder 101 encodes the input HDTV signals by a high 
efficiency encoding system combined from DCT and motion compensation 
predictive coding for data compression. 
The video compression encoder 101 outputs data of an intra-field or 
intra-frame coded picture, that is I-picture, data of a forward prediction 
coded picture or P-picture and data of a bidirectionally prediction coded 
picture or B-picture, in a pre-set sequence, as shown in FIG. 13. In the 
I-picture, DCT is applied independently without employing correlation with 
other pictures. In the P-picture, motion compensated prediction coding is 
done from previous I-picture or P-picture and the difference signal, or 
so-called prediction error, is discrete cosine transformed. In the 
B-picture, motion compensated predictive coding is done from the forward 
and backward I-picture or P-picture and the difference signals is 
similarly discrete cosine transformed. The period of appearance of the 
I-picture is termed a group of pictures (GOP). In the present case, M and 
N are set so that M=3 and N=9. 
A transport encoder 106 generates packets from video data encoded by the 
video compression encoder 101, audio data encoded by the audio encoder 104 
and the ancillary information supplied to an input terminal 107. 
FIG. 14 shows packet configuration. As shown therein, a transmitted packet 
has a packet length of 188 bytes. At the leading end of the packet is 
provided a linking header having a fixed 4-byte length and an adaptation 
header of a variable length, followed by transmission data consisting of 
video or audio data. 
In FIG. 12, the packet generated by the transport encoder 106 is supplied 
to a channel modulator 108 which modulates the packet using a carrier of a 
pre-set frequency. An output of the channel modulator 108 is issued at an 
output terminal 109. 
It is possible with the ATV system to transmit HDTV signals at a rate of 
e.g., 19 Mbps by the above-described picture compression. This is lower 
than the recording rate in the SD mode of the digital VTR (about 25 Mbps). 
Thus the signals (data) transmitted by the ATV system can be directly 
recorded with the SD mode of the digital VTR. If the transmitted signals 
are directly recorded by the digital VTR, there is no necessity of 
decoding HDTV signals from the transmitted signals and entering the 
decoded signals into the digital VTR thus obviating additional hardware. 
In addition, since recording may be done with the SD mode, the recording 
time may be prolonged. 
However, if the ATV signals are directly recorded with the SD mode on the 
digital VTR, variable-length reproduction cannot be achieved for the 
following reason. 
That is, compression (encoding) pursuant to the MPEG system is done with 
the ATV system, as explained above. With this system, data of an 
intra-field or intra-frame coded picture, that is I-picture, data of a 
forward prediction coded picture or P-picture and data of a 
bidirectionally prediction coded picture or B-picture are transmitted, as 
also explained above. During variable-speed reproduction, data of 
continuous pictures cannot be produced, because the head traverses the 
track on the magnetic tape. If the data of the continuous pictures is not 
produced, data of the P-picture and the B-picture cannot be decoded. It is 
only the intra-picture encoded data, that is I-picture data, that can be 
decoded. Thus, during variable-speed reproduction, the variable-speed 
reproduction is enabled by employing solely the data of the I-picture 
among the reproduced data. 
However, if the signals transmitted in accordance with the ATV system is 
directly recorded on the digital VTR, the packet carrying the I-picture 
cannot be sufficiently picked up during the variable-length reproduction. 
On the other hand, it is indefinite in which position the I-picture data 
is recorded. Thus it occurs frequently that data of the I-picture 
corresponding to a pre-set portion of the frame during variable-length 
reproduction is missing and the frame of such portion cannot be updated 
for a certain time thus deteriorating the picture quality. 
The present Assignee previously proposed an arrangement in which data of an 
I-picture is extracted from an input signal bitstream of the ATV system 
and recorded in an area for variable speed reproduction, while the signals 
of the ATV system are directly recorded in other areas, such as a video 
sector. The area for variable speed reproduction is an area from which 
reproduction may be done during variable speed reproduction. In this case, 
data from the area for variable speed reproduction is reproduced during 
variable speed reproduction and a frame is formed from the data of the 
I-picture reproduced from this area. 
The present Assignee also proposed the relevant technology in the following 
two Applications: 
i) European Patent Publication No. 0627855 (published data, 1994.12.07) 
ii) European Patent Publication No. 0650296 (published data, 1995.04.26. 
The U.S. application Ser. Nos. 08/327,370 (U.S. Pat. No. 5,684,917) and 
08/868,370, respectively, corresponding to these European Patent 
Publications are now pending at the US Patent Office. The above-mentioned 
applications, owned by the present Assignee, are hereby incorporated by 
reference. 
However, the reproducible area at the time of variable-speed reproduction 
is changed with the speed of the variable-speed reproduction. Thus it is 
difficult to set multiple variable playback speeds. For example, if data 
for variable-speed reproduction is recorded in a common area reproducible 
at 17-tuple, 9-tuple or quadruple speed, variable-speed reproduction at 
the quadruple speed, 9-tuple speed and 17-tuple speed becomes possible, 
while it is difficult to achieve variable-speed reproduction at any other 
speed. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a recording 
method and apparatus and a reproducing apparatus for digital video signals 
capable of easily variable-length reproducing ATV signals directly 
recorded on a recording medium at multiple variable playback speeds. 
According to the present invention, there is provided a method for 
recording digital video signals in which encoded digital video signals 
obtained on adaptively switching from intra-picture encoding to 
inter-picture encoding and vice versa are recorded as input data on each 
track of a magnetic tape by azimuth recording system. The method includes 
the steps of dividing each track of the magnetic tape into a first area 
and a second area, directly recording the input data in the first area of 
each track, and sequentially recording variable-speed playback data in the 
second area of each track. The variable-speed playback data is data among 
the input data which is obtained on intra-picture recording and which is 
collected from multiple regions divided from a full frame. 
According to the present invention, there is also provided an apparatus for 
recording digital video signals in which encoded digital video signals 
obtained on adaptively switching from intra-picture encoding to 
inter-picture encoding and vice versa are recorded as input data on each 
track of a magnetic tape by azimuth recording system. The apparatus has a 
first area in which the input data is directly recorded, a second area 
provided in each track of the magnetic tape for recording variable-speed 
playback data therein, and a signal processing circuit for extracting, 
from data derived from intra-picture encoding, the variable-speed playback 
data, collected from respective regions divided from a full frame, by 
variable speed playback data extracting means, to provide variable 
playback data, and for time-divisional multiplexing of the variable 
playback data and the input data by multiplexing means for recording on 
the track of the magnetic tape. 
According to the present invention, there is additionally provided an 
apparatus for reproducing digital video signals from a magnetic tape 
having a track having recorded thereon by an azimuth recording system 
encoded digital video signals obtained on adaptively switching from 
intra-picture encoding to inter-picture encoding and vice versa. The track 
has a first area in which the encoded digital video signals are directly 
recorded and a second area in which data among said input data which is 
obtained on intra-picture recording and which is collected from multiple 
regions divided from a full frame is sequentially recorded. The apparatus 
includes data separating means for separating data reproduced from the 
first area and data from the second area, from each other, and memory 
means having a storage capacity of storing one-frame data and supplied 
with data reproduced from the second area via the data separating means. 
The apparatus also has interpolating means for interpolating missing 
portions of data stored in the memory means during variable-speed 
reproduction and reproduced from the second area, and data switching means 
for selecting data reproduced from the first area and supplied from the 
data separating means during normal reproduction and selecting data 
interpolated by the interpolating means during variable-speed 
reproduction. The apparatus also includes a signal processing circuit for 
interpolating missing portions of data reproduced from the second area 
during variable-speed reproduction and for outputting the interpolated 
data as playback data for one frame. 
With the method for recording digital video signals according to the 
present invention, each track of the magnetic tape has a first area and a 
second area, the input data is directly recorded in the first area of each 
track, and sub-sampled set data for variable-speed reproduction is 
sequentially recorded in the second area of each track, which sub-sampled 
data set is data among said input data which is obtained on intra-picture 
recording and which is collected from multiple regions divided from a full 
frame. 
With the apparatus for recording digital video signals according to the 
present invention, a first area in which the input data is directly 
recorded and a second area provided in each track of the magnetic tape for 
recording variable-speed playback data are provided in each track of the 
magnetic tape, and the variable-speed playback data, collected from 
respective regions divided from a full frame, are extracted from data 
derived from intra-picture encoding by variable speed playback data 
extracting means to provide variable playback sub-sampled data set, and 
for time-divisional multiplexing of the variable playback sub-sampled data 
set and the input data by multiplexing means for recording on the track of 
the magnetic tape. Thus a full frame picture may be constituted on 
reproducing the sub-sampled set data so that variable-speed reproduction 
may be achieved at an optional speed. 
On the other hand, with the reproducing apparatus for reproducing digital 
video signals according to the present invention, data for variable-speed 
playback reproduced from the second area may be stored in memory means and 
missing data portions may be interpolated by interpolating means for 
producing playback data of high picture quality. 
Thus the present invention provides a recording method and apparatus and a 
reproducing apparatus for digital video signals whereby ATV signals 
directly recorded on a recording medium may be easily variable-speed 
reproduced at an optional variable reproducing speed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring to the drawings, preferred embodiments of the recording method 
and apparatus and the reproducing apparatus for digital video signals 
according to the present invention are disclosed. 
FIG. 1 shows, in a block diagram, a configuration of a video 
recording/reproducing system employing a digital VTR according to the 
present invention. In this figure, signals of the ATV system, that is 
modulated transmission data, enter a channel demodulator 1. The channel 
data modulator 1 demodulates modulated transmission data to reproduce 
packets of transmission data. 
A digital VTR 3 of the azimuth recording system includes an interfacing and 
format converting section 4 and a recording/reproducing section 5. Data 
packets from the channel modulator 1 are supplied via the interfacing and 
format converting section 4 to a transport decoder 6, while being also 
supplied to the recording/reproducing section 5. The data supplied to the 
recording/reproducing section 5 via the interfacing and format converting 
section 4 is recorded in the recording/reproducing section 5 on the 
magnetic tape by a rotary head. The interfacing and format converting 
section 4 formats data sent to the recording/reproducing section 5, so 
that, when the data recorded by the recording/reproducing section 5 is 
reproduced, an optimum picture will be reproduced, in a manner to be 
explained subsequently. 
The recording/reproducing section 5 discrete cosine transforms and variable 
length encodes the video signals by way of signal compression to record 
the resulting compressed data by the rotary head on the magnetic tape. 
That is, the recording/reproducing section 5 can be set to the SD mode of 
recording video signals of the NTSC system or the HD mode of recording 
HDTV signals. When directly recording the ATV system signals, supplied via 
the interfacing and format converting section 4, that is the transmission 
data, the recording/reproducing section 5 is set to the SD mode. 
The transport decoder 6 corrects errors of data packets supplied thereto 
via the interfacing and format converting section 4, while taking out data 
and ancillary information from the data packets. 
A video expansion decoder 7 decodes the Huffman code and effects inverse 
DCT for expanding the data supplied thereto in order to form baseband 
signals of the HDTV system. The video expansion decoder 7 and the audio 
decoder 8 are fed with an output of the transport decoder 6. The video 
expansion decoder 7 expands the transmitted data and converts them into 
analog signals in order to form HDTV signals. 
The HDTV signals, thus formed, are outputted at an output terminal 9. The 
audio data is decoded by the audio decoder 8 to generate audio signals 
which are outputted at an output terminal 10. The output ancillary 
information from the transport decoder 6 is outputted at an output 
terminal 11. 
FIG. 2 shows, in a block diagram, a configuration of a recording system of 
a digital VTR 3 according to the present invention. 
In FIG. 2, the numeral 21 denotes an input terminal for video signals of 
the current television system, such as the NTSC system, or HDTV signals. 
For recording video signals from outside, component video signals of the 
video signals of the current television system or HDTV system are supplied 
to the input terminal 21. The component video signals from the input 
terminal 21 are supplied to an A/D converter 22 so as to be converted into 
digital signals. 
A DCT compression processing circuit 23 encodes and compresses input video 
signals by DCT and VLC. That is, the component video signals, converted 
into digital signals from the A/D converter 22, are supplied to DCT 
compression processing circuit 23 so as to be blocked, shuffled and 
discrete cosine transformed to produce data (so-called DCT coefficients) 
which are buffered with a pre-set buffer unit. The total buffer-based code 
quantity is estimated and an optimum quantization table which will give 
the total code quantity less than a pre-set value is determined. 
Quantization is done in accordance with this optimum quantization table. 
The resulting quantized data is variable length encoded and subsequently 
framed. 
A switching circuit 24 is switched between recording the transmitted ATV 
system signals and recording the video signals from the input terminal 21. 
The switching circuit 24 has its fixed input terminal 24A supplied with 
the ATV signals via the interfacing and format converting section 4. On 
the other hand, the switching circuit 24 has its fixed input terminal 24B 
supplied with an output of the DCT compression processing circuit 23. For 
recording the transmitted ATV system signals, the switching circuit 24 is 
set to the side of the fixed input terminal 24A. For recording the video 
signals from the input terminal 21, the switching circuit 24 is set to the 
side of the fixed input terminal 24B. 
A framing section 25 frames recording data, supplied thereto via the 
switching circuit 24, into a pre-set sync block, while effecting error 
correction. 
An output of the framing section 25 is fed to a channel encoder 26 and 
thereby modulated. An output of the channel encoder 26 is supplied via a 
recording amplifier 27 to a rotary head 28. The rotary head 28 records 
compressed video signals or HDTV signals from the input terminal 21 or the 
ATV signals from the input terminal 2. 
That is, for recording the transmitted ATV system signals in the 
above-described recording system, the switching circuit 24 is set to the 
side of the fixed input terminal 24A. Thus the ATV system signals, 
supplied via the interfacing and format converting section 4, are framed 
by the framing section 25 and modulated by the channel encoder 26 so as to 
be recorded by the rotary head 28 on the magnetic tape. 
On the other hand, for recording video signals from the input terminal 21, 
the switching circuit 24 is set to the side of the fixed input terminal 
24B. Thus the video signals from the input terminal 21 are encoded and 
compressed by the DCT compression processing circuit 23 and framed by the 
framing circuit 25 so as to be then modulated by the channel encoder 26 
and subsequently recorded by the rotary head 28 on the magnetic tape. 
For recording the ATV system signals, the interfacing and format converting 
section 4 arranges data so that an area reproducible during variable-speed 
reproduction will be a trick play area and data of an I-picture (DCT 
coefficients of a fixed length) will be recorded in this trick play area, 
in order to improve the picture quality for variable-speed reproduction, 
as will be explained subsequently. During variable-speed reproduction, the 
I-picture data is read out from this trick play area and decoded. 
FIG. 3 shows, in a block diagram, a configuration of a reproducing system 
of the digital VTR 3. In this figure, recorded signals of a magnetic tape 
are reproduced by the rotary head 28 and sent via a playback amplifier 51 
to a channel decoder 52. The channel decoder demodulates the playback 
signals in accordance with a demodulating system which is a counterpart of 
the modulating system of the channel encoder 26 of the recording system 
described above. 
A time base corrector (TBC) 53 eliminates jitter in the playback signals. 
That is, the TBC 53 is fed with write clocks and readout clocks, which are 
respectively based on the playback signals and on reference signals, while 
being also fed with an output of the channel decoder 52. The TBC 
eliminates jitter in the playback signals. 
A deframing section 54 is a counterpart of the framing section 25 of the 
recording system, and corrects errors in the playback data from the TBC 
53. 
A switching circuit 55 is switched between reproducing the ATV system 
signals and reproducing component video signals. An output of the 
deframing section 54 is supplied to a switching circuit 55. If the 
playback signals are ATV system signals, the switching circuit 55 is 
switched to the side of a fixed input terminal 55A. If the playback 
signals are component video signal, the switching circuit 55 is switched 
to the side of a fixed input terminal 55B. 
A DCT expansion circuit 56 is a counterpart of the DCT compression 
processing circuit 23. That is, the DCT expansion circuit 56 decodes 
variable length codes, which are playback data, and inverse discrete 
cosine transforms the decoded data for expanding the compression-recorded 
component video signals into the original baseband video signals. That is, 
an output of the fixed input terminal 55B of the switching circuit 55 is 
supplied to the DCT expansion circuit 56 whereby playback data is restored 
to baseband video signals which are outputted at an output terminal 57. 
An output of the terminal 55A of the switching circuit 55 is supplied to a 
packet selection circuit 59. For usual reproduction of the ATV system 
signals, the packet selection circuit 59 selects all of the packets of the 
playback data supplied thereto via the switching circuit 55. On the other 
hand, for variable speed reproduction, only I-picture data are valid. 
Thus, for variable speed reproduction, the packet selection circuit 59 
selects and outputs data packets of the I-picture data obtained on 
reproducing the trick play area. An output of the packet selection circuit 
59 is issued at an output terminal 60. 
A controller 61 performs control of switching between normal reproduction 
and variable speed reproduction. The controller 61 is fed with a mode 
setting signal from an input section 62. A servo circuit 63 and the packet 
selection circuit 59 are controlled responsive to this mode setting 
signal. During variable speed reproduction of the ATV system signals, the 
servo circuit 63 effects phase control and tape speed control by 
exploiting tracking signals, such as ATF signals, for fixing the phase so 
that the position traced by the head will be perpetually the same position 
on the track. That is, during variable speed reproduction, the trick play 
area is reproduced, so that the I-picture data recorded in the trick play 
area will be reproduced. 
An output of the output terminal 60 is sent to the video expansion decoder 
7 of FIG. 1 for decoding. In the present embodiment, all I-picture data 
for one full frame is recorded in the trick play area. Consequently, 
during variable-speed reproduction, the actual picture is updated with one 
full frame as a unit, thus giving an easy-to-see reproduced picture. 
The variable speed reproduction in the digital VTR according to the present 
invention is explained in detail. 
FIG. 4 shows the configuration of one track in the present digital VTR. 
Each track is constituted by an audio sector SEC1, a video sector SEC2 and 
a subcode sector SEC3. The video sector SEC2 has a capacity corresponding 
to video data of 135 sync blocks, as shown in FIG. 5. A 5-byte sync and ID 
are appended at the leading end of each sync block. Spare data (VAUX) 
corresponding to 3 sync blocks are appended to these video data. Using 
product codes, double error correction codes (C1 and C2) are appended. 
Thus the video data corresponding to 135 sync blocks can be recorded in 
each track of the video sector SEC2. For the SD mode, the rpm of the 
rotary drum is 150 Hz. Two heads with different azimuth angles are mounted 
on the rotary drum so that data is azimuth-recorded on ten tracks per 
frame. For recording ATV system signals, that is ATV signals, the data 
area in each sync block (1 SB) is 77 bytes or 77.times.8=616 bits, as 
shown in FIG. 6. 
Assuming that each frame of a color input picture having a 4:2:0 structure 
is made up of 1920.times.10180 pixels, the number of DCT blocks for 
luminance data in one frame is (1920/8).times.(1080/8)=240.times.135 DCT 
blocks, while that for chrominance data is 
(240/2).times.(135/2)=120.times.68 DCT blocks. 
Then, as shown in FIG. 7, a frame is divided in ten in the horizontal 
direction and in six in the vertical direction. From each divided area, 1 
DCT block is picked up, and 9 dummy blocks are provided. Thus, luminance 
data becomes (240/10).times.((135+9)/6)=24.times.24 blocks. On the other 
hand, 4 dummy blocks are provided, so that each chrominance data becomes 
(120/10).times.((68 +4)/6)=12.times.12 blocks. These blocks are termed 
sub-sampled DC coefficient sets. 
A first set of sub-sampled DC coefficients, denoted by .smallcircle. in 
FIG. 7, is collected and sequentially recorded in the trick play area. 
Then, another set of sub-sampled DC coefficients, denoted by 
.circle-solid. in FIG. 7, is collected and sequentially recorded in the 
trick play area. In this manner, all DC coefficient data in one frame are 
recorded in the trick play areas TP, as shown in FIG. 8. 
If the DC coefficient data is 10 bits, each set of the sub-sample DC 
coefficients is 10.times.6.times.10=600 bits, so that it can be recorded 
in the above-mentioned sync bit of 616 bits. 
Consequently, during reproduction, each frame can be constituted by 
sub-sampled DC coefficients, if 1SB can be reproduced. In effect, 3 SBs of 
the luminance data and chrominance data give sub-sampled DC coefficient 
sets capable of constituting one frame. With the 4:2:0 structure color 
picture data, since the number of the chrominance data is one-half that of 
the luminance data, the chrominance data can be recorded twice by way of 
duplex recording. 
For variable-speed reproduction, if the reproducing speed is such that 
three or more SBs exist in each burst, data of the sub-sampled DC 
coefficient sets for one frame can be reproduced at an arbitrary speed. On 
the other hand, the lower the speed, the shorter is the interval between 
head scans, so that data of many sub-sample DC coefficient sets can be 
reproduced. An actual playback picture is constituted by interpolating 
other non-reproduced DC coefficient data with data of the sub-sampled DCT 
coefficient sets. Consequently, since data of many sub-sampled DC 
coefficient sets can be reproduced at lower speeds, the sub-sampling 
interval becomes shorter to enable a picture of a higher quality to be 
constituted. 
If the trick play area for one track is 3 SBs, trick play data is recorded 
over 24.times.24=576 tracks. Thus, all I-pictures can not necessarily be 
recorded, resulting in the lowering of the updating ratio during playback. 
For example, if the trick play area for one track is of 12 SBs, it can be 
recorded with 576/(12/3)=144 tracks. 
As shown by four shaded areas of a track in FIG. 8, plural trick play 
areas, inclusive of the trick play area in black, may be provided for one 
track. Such plural tracks may be arranged side-by-side. 
FIG. 9 schematically illustrates recording/reproduction of ATV signals. A 
main area Al and a trick play area A2 are provided on a video sector of a 
magnetic tape 31. The trick play area A2 corresponds to the 
above-described allowance recording area which is provided in an area 
reproducible during variable-speed reproduction. During recording, an 
input bitstream of ATV signals or a data stream is directly recorded in 
the main area A1, while being supplied to a VLD decoding circuit 34. The 
VLD decoding circuit 34 decodes the ATV signals to detect breaking points 
of the variable length encoded DCT coefficients in order to transmit fixed 
length DC coefficient data to a data separating circuit 36. 
Based upon the sub-sampled pattern supplied from the sub-sampled pattern 
generator 35, the data separating circuit 36 extracts sub-sampled DC 
coefficient data, as data required for variable-length reproduction, from 
the bitstream of the DC coefficient data supplied form the VLD decoding 
circuit 34, based upon the sub-sampled pattern supplied from the 
sub-sampled pattern generator 35. 
The data required for variable-speed reproduction are only DC coefficient 
data of respective blocks of the I-picture of ATV signals. The I-picture 
data required for this variable-speed reproduction is supplied to an EOB 
appending circuit 37. The EOB appending circuit 37 appends an EOB 
specifying an end of block. The data for the I-frame necessary for 
variable-speed reproduction, that is DCT coefficient data of respective 
blocks of the I-picture, is recorded in the trick play area A2 as 
sub-sampled DC coefficient set data. 
During normal reproduction, playback signals from the main area A1 are 
decoded. During variable-speed reproduction, only the trick play area A2 
is reproduced and decoded. Consequently, during variable-length 
reproduction, only DC coefficient data of respective blocks of the 
I-picture are sent to the video expansion decoder 7. In order for these 
data to be decoded by a usual video expansion decoder, the transmitted 
data construction must be the same as the construction of a usual 
bitstream. For this reason, the EOB data specifying end of block is 
appended after extraction of the dc component from the respective blocks 
during recording. 
The illustrative construction of the interfacing and format converting 
section 4, framing section 25, deframing section 54 and thee packet 
selection circuit 59, making up the present digital VTR, is now explained. 
The circuits having the same functions as those of the circuits shown in 
FIGS. 1 to 3 and 9 are denoted by the same numerals and the corresponding 
explanation is omitted. 
Referring to FIG. 10, the interfacing and format converting section 4 
constituting the recording system of the digital VTR 3 includes a buffer 
memory 71 for temporarily storing ATV signals, and a demultiplexor 72 for 
extracting video signal packets from the ATV signals. The interfacing and 
format converting section 4 also includes a depacketing circuit 73 for 
resolving the video signal packets from the demultiplexor 72 into 
respective packets, and a syntax analysis circuit 74 for analyzing the 
header of each packet for extracting I-picture data. The interfacing and 
format converting section 4 also includes the above-mentioned VLD decoding 
circuit 34 for detecting the breaking points of the DCT coefficients and 
the above-mentioned data separating circuit 36 for extracting trick play 
data made up of sub-sampled DC coefficient sets of the DCT coefficient 
data of respective blocks of the I-picture based upon the sub-sampled 
pattern supplied from the sub-sampled pattern generator 35. The 
interfacing and format converting section 4 finally includes a multiplexor 
75 for time-divisionally multiplexing trick play data from the data 
separating circuit 36 and ATV signals stored in the buffer memory 71, and 
a control circuit 76 for controlling the multiplexor 75. 
The interfacing and format converting section 4 is so configured that, when 
it extracts trick play data required for variable-speed reproduction from 
the ATV signals and inserts the trick play data into the ATV signals for 
forming recording data by time-divisional multiplexing, the distance from 
a recording start position to the trick play area on each track differs 
between neighboring blocks. 
That is, the buffer memory 71 temporarily stores the input ATV signals and 
reads out the stored ATV signals on e.g., a sync block basis in order to 
transmit the read-out signals to the multiplexor 75. 
On the other hand, the demultiplexor 72 extracts the video signal packets 
from the ATV signals to supply the extracted packets to the depacketing 
circuit 73 which then resolves the video signal packets into respective 
packets. 
The syntax analysis circuit 74 analyzes the headers of the respective 
packets resolved by the depacketing circuit 73 and extracts the packets 
containing the I-picture data. The extracted packets are supplied to the 
data separating circuit 36. 
The VLD decoding circuit 34 decodes the packets supplied from the 
depacketing circuit 73 and detects the breaking point of the variable 
length encoded DCT coefficients to transmit the fixed-length DCT 
coefficients to the data separating circuit 36. 
The data separating circuit 36 extracts, from the data of the packets 
supplied from the VLD decoding circuit 34, trick play data made up of 
sub-sampled DCT coefficient sets of the DCT coefficient data of respective 
blocks of the I-picture, based upon the sub-sampling pattern supplied from 
the sub-sampling pattern generator 35, and transmits the extracted data to 
the EOB appending circuit 37. The EOB appending circuit 37 appends the EOB 
to the low-range coefficients of the respective blocks of the I-picture 
and transmits the resulting data on the sync block basis to the 
multiplexor 75. 
The multiplexor 75 time-divisionally multiplexes the ATV signals read out 
from the buffer memory 71 and the trick play data from the data separating 
circuit 36. 
That is, the control circuit 76 time-divisionally multiplexes the ATV 
signals read out from the buffer memory 71 and the trick play data from 
the data separating circuit 36. The recording data thus obtained on 
time-divisionally multiplexing the ATV signals and the trick play data are 
supplied via the switching circuit 24 shown in FIG. 2 to the framing 
section 25. 
The framing section 25 has a C2 parity circuit 77 for appending the outer 
parity and a framing circuit 78 for appending the inner parity, as shown 
in FIG. 10. The C2 parity circuit 77 appends the outer parity C2 to 
recording data supplied from the multiplexor 75, while the framing circuit 
78 appends the inner parity C1 and the 5-byte sync and ID to the recording 
data and transmits the resulting data to the channel encoder 26. 
Thus the sub-sampling DCT coefficient sets of the DCT coefficient data of 
respective blocks of the I-picture are recorded on the trick play area. 
The deframing section 54, constituting the reproducing system of the 
digital VTR 3, includes a deframing circuit 81 for correcting the playback 
data for error by the inner parity C1 and for correcting the playback data 
for error by the outer parity C2, as shown in FIG. 11. 
The deframing circuit 81 corrects the playback data supplied from the 
channel decoder 52 via the TBC 53 shown in FIG. 3 for errors by the inner 
parity C1 and routes the resulting data to the error correcting circuit 
82. 
The error correcting circuit 82 corrects the playback data supplied during 
normal reproduction for errors by the outer parity C2. However, the error 
correcting circuit 82 does not perform error correction during 
variable-speed reproduction of ATV signals, that is, it does not correct 
the playback data constituted solely by the trick play data for errors. An 
output of the error correction circuit 82 is supplied via the switching 
circuit 55 shown in FIG. 3 to the DCT expansion circuit 56 and via the 
switching circuit 55 to the packet selection circuit 59 during 
reproduction of the component video signals and during reproduction of the 
ATV signals, respectively. 
Turning again to FIG. 11, the packet selection circuit 59 includes a 
demultiplexor 83 for distributing playback data between normal 
reproduction and variable-speed reproduction, and a buffer memory 84 for 
temporarily storing playback data during variable-speed reproduction. The 
circuit 59 also includes an interpolation circuit 85 for interpolating the 
playback data stored in the buffer memory 84, an error processing circuit 
86 for setting data not corrected for errors by the inner parity C1 to 
zero, and a selector 87. 
The demultiplexor 83 decodes the packets of the ATV signals and transmits 
all packets of the playback data supplied from the error correcting 
circuit 82 to the selector 87 during normal reproduction of the ATV 
signals while transmitting sub-sampled DCT coefficient sets of the DCT 
coefficient data of respective blocks of the I-picture reproduced as the 
trick play data required for variable-speed reproduction from the trick 
play area to the buffer memory 84 during variable-speed reproduction. 
The buffer memory 84 temporarily stores data of the sub-sampled DCT 
coefficient data reproduced from the trick play area and, at a time point 
when data for one full frame is readied, transmits the stored DCT 
coefficient data via the interpolating circuit 85 to the error processing 
circuit 86. The interpolating circuit 85 interpolates other DCT 
coefficient data, which have failed to be reproduced, with data of the 
sub-sampled DCT coefficient sets supplied from the buffer memory 84. The 
error processing circuit 86 sets data, for which error correction was 
unable to be done in the deframing circuit 81 with the aid of the inner 
parity C1, to zero, and transmits data of the I-picture, made up of DCT 
coefficient data for one frame interpolated by the interpolating circuit 
85, to the selector 87. 
The selector 87 selects the playback data directly supplied from the 
demultiplexor 83 during normal reproduction of the ATV signals, while 
selecting the playback data supplied from the error processing circuit 85 
during variable-speed reproduction. The selector routes the selected data 
to the video expansion decoder 7 shown in FIG. 1. 
In the trick play area, one full frame of the I-picture, made up only of 
DCT coefficients, is recorded. If simply the reproduced picture is sent to 
the video expansion decoder 7, there is no assurance that the display 
timing (1/30 second) be matched to the timing of the I-picture boundary, 
such that the actual picture is not updated on the frame basis but only 
partial updating results. Thus, before sending playback data to the video 
expansion decoder 7, one-frame data is fully reproduced and readied and 
subsequently the playback data is supplied to the video expansion decoder 
7. This enables an actual picture to be updated on the frame basis to 
permit a variable-speed reproduced picture which is easy to view. It is 
also possible to use a common buffer memory for the buffer memory 71 of 
the recording system and for the buffer memory 84 of the playback system 
and to switch the common buffer for recording and reproduction. 
Although the foregoing description has been made of the digital VTR 
configured for recording ATV system signals, it is to be noted that the 
present invention may be applied to a VTR configured for recording input 
data obtained on encoding video signals adaptively switched between 
intra-picture encoding and inter-picture predictive encoding.