U.S. patent application number 10/839207 was filed with the patent office on 2004-10-14 for digital vtr.
This patent application is currently assigned to Mitsubishi Denki Kabushiki Kaisha. Invention is credited to Asamura, Masako, Hibi, Taketoshi, Inoue, Tohru, Ishimoto, Junko, Kurahashi, Satoshi, Onishi, Ken, Ueda, Tomohiro, Yamasaki, Tatsuo.
Application Number | 20040202451 10/839207 |
Document ID | / |
Family ID | 33136404 |
Filed Date | 2004-10-14 |
United States Patent
Application |
20040202451 |
Kind Code |
A1 |
Asamura, Masako ; et
al. |
October 14, 2004 |
Digital VTR
Abstract
In a digital VTR having a certain recording bit rate, within a
range not higher than a remaining data rate after recording the bit
stream, first HP data D1 is recorded in first specific regions, and
second HP data D2 is recorded in second specific regions in
specific tracks. In middle-speed and high-speed fast replay, the
magnetic tape is transported continuously at a middle-speed or
high-speed higher than the standard speed for normal replay, and
the first HP data D1 is used in common, and at a low-speed fast
replay of about twice the normal speed, the speed of the magnetic
tape is alternated between a speed near the standard speed for
normal replay, and a speed near the low-speed fast, and at the
speed near the standard speed, the second HP data disposed in the
second specific regions in the specific tracks and the first HP
data disposed in the first specific regions in the specific tracks
are both replayed.
Inventors: |
Asamura, Masako;
(Nagaokakyo-shi, JP) ; Kurahashi, Satoshi;
(Nagaokakyko-shi, JP) ; Ueda, Tomohiro;
(Nagaokakyo-shi, JP) ; Hibi, Taketoshi;
(Nagaokakyo-shi, JP) ; Yamasaki, Tatsuo;
(Nagaokakyo-shi, JP) ; Ishimoto, Junko;
(Nagaokakyo-shi, JP) ; Inoue, Tohru;
(Nagaokakyo-shi, JP) ; Onishi, Ken;
(Nagaokakyo-shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
Mitsubishi Denki Kabushiki
Kaisha
|
Family ID: |
33136404 |
Appl. No.: |
10/839207 |
Filed: |
May 6, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10839207 |
May 6, 2004 |
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09541088 |
Mar 31, 2000 |
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09541088 |
Mar 31, 2000 |
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08925074 |
Sep 8, 1997 |
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6081649 |
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08925074 |
Sep 8, 1997 |
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08417107 |
Apr 5, 1995 |
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Current U.S.
Class: |
386/345 ;
386/E5.052; 386/E9.013; 386/E9.052; 386/E9.059; G9B/15.011;
G9B/15.021; G9B/15.03; G9B/27.002; G9B/27.033 |
Current CPC
Class: |
G11B 15/4673 20130101;
H04N 9/888 20130101; G11B 15/1875 20130101; G11B 27/3027 20130101;
G11B 2220/90 20130101; G11B 15/18 20130101; H04N 5/783 20130101;
G11B 15/52 20130101; G11B 27/005 20130101; H04N 9/8227 20130101;
H04N 5/78263 20130101; H04N 9/877 20130101; G11B 15/087 20130101;
H04N 9/8042 20130101 |
Class at
Publication: |
386/068 ;
386/111; 386/112 |
International
Class: |
H04N 005/783 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 12, 1994 |
JP |
6-99370 |
Apr 14, 1994 |
JP |
6-102235 |
Apr 15, 1994 |
JP |
6-102206 |
Apr 21, 1994 |
JP |
6-107985 |
May 10, 1994 |
JP |
6-121718 |
Aug 8, 1994 |
JP |
6-186036 |
Claims
1. A playback device for replaying a bit stream digitally
transmitted, comprising: detecting means for detecting
intra-picture data in the bit stream that is replayed; extracting
means for extracting the intra-picture data from the replayed bit
stream, according to the result of the detection at the detecting
means; replay mode designating means for selecting and designating
one of normal replay, slow replay and still replay, as a replay
mode; and replay data outputting means for storing the extracted
intra-picture data, and outputting the intra-picture data as the
replay picture data, according to a mode signal output by said
replay mode designating signal.
2. A playback device as set forth in claim 1, wherein said replay
data output means comprises: address detecting means for detecting
an address at which the intra picture data is recorded; control
means for causing normal speed replay and reversing, for reverse
control, on the basis of the result of the detection of the
address.
3. A playback device as set forth in claim 1, wherein said replay
data output means comprises: control means for stopping the replay
for a predetermined period after all the intra-picture data is
extracted from the bit stream by normal speed replay.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a digital video tape
recorder (herein after referred to as digital VTR) having a track
format for recording digital video and audio signals in
predetermined areas on oblique track, and relates to a digital VTR
in which the digital video and audio signals are input in the form
of a bit stream, and the bit stream is magnetically recorded and
replayed (played back).
[0002] FIG. 41 is a diagram showing a track pattern of a
conventional, general consumer digital VTR. Referring to the
drawing, a plurality of tracks are formed on a magnetic tape 310,
in a head scanning direction inclined to the tape transport
direction, and digital video and audio signals are recorded
therein. Each track is divided into two areas, a video area 312 for
recording a digital video signal and an audio area 314 for
recording a digital audio signal.
[0003] Two methods are available for recording video and audio
signals on a video tape for such a consumer digital VTR. In one of
the methods, analog video and audio signals are input, and
recorded, using a video and audio high-efficiency encoding means;
this is called a baseband recording method. In the other method,
the bit stream having been digitally transmitted; this method is
called a transparent recording method.
[0004] For the system of recording ATV (advanced television)
signals, now under consideration in the United States, the latter,
transparent recording method is suitable. This is because the ATV
signal is digitally compressed signals, and does not require a
high-efficiency encoding means or a decoding means, and because
there is no degradation in the picture quality due to
transmission.
[0005] The transparent recording system however is associated with
a problem in the picture quality in a special replay mode, such as
a high-speed replay mode, a still replay mode and a slow replay
mode. In particular, when a rotary head scans the tape obliquely to
record a bit stream, almost no image is replay at the time of
high-speed replay, if not specific measure is taken.
[0006] An improvement for the picture quality for the transparent
recording system recording the ATV signal is described in an
article Yanagihara, et al, "A Recording Method of ATV data on a
Consumer Digital VCR", in International Workshop on HDTV, 93, Oct.
26 to 28, 1993, Ottawa, Canada, Proceedings, Vol. II. This proposal
is now explained.
[0007] With one basic specification of a prototype consumer digital
VTR, in the SD (standard definition) mode, when the recording rate
of the digital video signal is 25 Mbps, and the field frequency is
60 Hz, two rotary heads are used for recording a digital video
signal of one frame, being divided into video areas on 10 tracks.
If the data rate of the ATV signal is 17 to 18 Mbps, transparent
recording of the ATV signal is possible with the recording rate in
this SD mode.
[0008] FIG. 42A and FIG. 42B show tracks formed in a magnetic tape
using a conventional digital VTR. FIG. 42A is a diagram showing
scanning traces of the rotary heads during normal replay. FIG. 42B
shows scanning traces of the rotary heads during high-speed replay.
In the example under consideration, the rotary heads are provided
in opposition, 180.degree. spaced apart on a rotary drum, and the
magnetic tape is wrapped around over 180.degree.. In the drawing,
adjacent tracks on the tape 310 are scanned by two rotary heads A
and B having different azimuth angles, alternately and obliquely,
to record digital data. In normal replay, the transport speed of
the tape 310 is identical to that during recording, so that the
heads trace along the recorded tracks. During high-speed replay,
the tape speed is different, so that the heads A and B traces the
magnetic tape 310 crossing several tracks. The arrow in FIG. 42B
indicates a scanning trace by a head A at the time of five-time
high-speed feeding. The width of arrow represents the width of the
region read by the head. Fractions of digital data recorded on
tracks having an identical azimuth angle are replayed from regions
meshed in the drawings, within five tracks on the magnetic tape
310.
[0009] The bit stream of the ATV signal is according to the
standard of the MPEG2. In this bit stream according to the MPEG2,
only the intra-frame or intra-field encoded data of the video
signal, i.e., the data of intra encoded block (intra encoded block)
alone can be decoded independently, without reference to data of
other frame or field. Where the bit stream is recorded in turn on
the respective tracks, the recorded data are replayed
intermittently from the tracks during fast replay, and the image
must be reconstructed from only the intra-encoded blocks contained
in the replay data. Accordingly, the video area updated on the
screen is not continuous, and only the fractions of data of intra
coded block are replayed, and may be scattered over the screen. The
bit stream is variable-length encoded, so that it is not ensured
that all the replay data over the screen is periodically updated,
and the replay data of certain parts of the vide area may not be
updated for a long time. As a result, this type of bit stream
recording system does not provide a sufficient picture quality
during fast replay in order to be accepted as a recording method
for a consumer digital VTR.
[0010] FIG. 43 is a block configuration diagram showing an example
of recording system in a conventional digital VTR. Referring to the
drawing, reference numeral 1 denotes an input terminal for the bit
stream, 2 denotes an HP data format circuit, and 3 denotes a
recording format circuit. Reference numeral 4 denotes a
variable-length decoder, 5 denotes a counter, 6 denotes a data
extractor, 7 denotes a EOB (end of block) appending circuit, and 8
denotes an output terminal.
[0011] The video area in each track is divided into a main area for
recording the bit stream of the ATV signal, and copy area for
recording important part (HP data) of the bit stream which are used
for reconstruction of the image in fast replay. Only the
intra-encoded blocks are effective during fast replay, so that they
are recorded in the copy area. To reduce the data further, the only
the low-frequency components are extracted from all the
intra-encoded blocks, and recorded as HP data.
[0012] The bit stream of MPEG2 is input via the input terminal 2,
and led to the recording format circuit 3. The bit stream from the
input terminal 1 is also input to the variable-length decoder 4,
and the syntax of the bit stream of the MPEG2 is analyzed, and the
intra-picture data is detected, and timing signals are generated by
the counter 5, and the low-frequency components of all the blocks
in the intra-picture data are extracted. Furthermore, EOBs are
appended at the EOB appending circuit 7, and HP data is constructed
at the HP data format circuit 2. At the recording data format
circuit 3, the HP data and the bit stream to be recorded in the
main area are combined into a format suitable for recording in one
track, and output via the output terminal 8, and respectively
recorded in the main area and the copy area.
[0013] FIG. 44 shows a recording format on the tape. The
combination of an alphabetic character A, B, C, and succeeding
numerals 0, 1, 2 indicate the areas where HP data are recorded.
Different data Ai, Bi, Ci (i=0, 1, 2, . . . ) are recorded in each
track. An identical set of data Ai, Bi and Ci are repeatedly
recorded over 17 tracks within a range indicated by RP.
[0014] FIG. 45A and FIG. 45B show an example of replay system in a
conventional digital VTR. FIG. 45A schematically shows normal
replay. FIG. 45B schematically shows fast replay.
[0015] Separation of data from the magnetic tape during normal
replay and fast replay are performed respectively in the following
ways. During normal replay, the bit stream recorded in the main
areas 270 is all replayed, and the bit stream from the data
separation circuit 272 are sent as the normal replay data, to an
MPEG2 decoder, provided outside the replay system. The HP data from
the copy area 271 are discarded. During fast replay, only the HP
data from the copy area 271 are collected, and sent, as fast replay
data, to the decoder. At the data separation circuit 272, the bit
stream from the main areas 270 is abandoned.
[0016] A method of fast replay from a track in which a main area
270 and copy areas 271 is next described. FIG. 46A shows a scanning
trace of a head. FIG. 46B shows a track regions from which the
replay is possible. When the tape speed is an integer multiple of
the normal replay speed, if phase-locking control is conducted by
an ATF (automatic track following) method or the like for tracking
by moving the head itself, the head scanning is in a predetermined
phase relationship with tracks having an identical azimuth. As a
result, the data replayed by the head A from the tracks recorded
alternately by the heads A and B, are fixed to those from the
meshed regions.
[0017] In FIG. 46B, if the signal having an output level larger
than -6 dB is replayed by the heads, the data is replayed by one
head from the meshed tape regions. The drawing show an example of
nine-time speed replay. If replay of the signals from the meshed
regions is ensured at the nine-time replay, the regions are used as
copy areas, and the HP data are recorded in the copy areas, so that
the reading of the HP data from these regions at this speed is
possible. However, reading of these signals at different speeds is
not ensured. Accordingly, a plurality of areas need to be selected
for the copy areas, so that the replay signals can be read at
different tape speeds.
[0018] FIG. 47 shows regions where the copy areas overlap for a
plurality of different replay speeds. It shows examples of scan
regions for three different tape speeds, for cases where the head
is in synchronism with a track of an identical azimuth. The scan
regions where the reading by the head is possible at different tape
speeds overlap, at some of the regions. By selecting the regions at
which the overlapping occurs as the copy areas, reading of the HP
data at different tape speeds can be ensured. The drawings show the
regions at which overlapping occurs at the feed-forward at
four-time, nine-time, 17-time speed. Theses scan regions are
identical to those of feed-forward at -2 time, -7 time and -15 time
high speeds (i.e., rewind at 2 time, 7 time and 15 time
speeds).
[0019] Even though there are overlapping regions for different tape
speeds, it is not possible to determine a recording pattern so that
identical regions are always traced at different speeds. This is
because the number of tracks crossed by the head differ depending
on the tape speed. Moreover, it is necessary for the head to be
capable of starting tracing at whichever identical azimuth track.
For this reason, identical HP data is repeatedly recorded over a
plurality of tracks, to solve the above problem.
[0020] FIG. 48 shows examples of scanning traces of the rotary head
at different tape speeds. Regions 1, 2 and 3 are selected from
among the overlapping regions for five-time and nine-time speeds.
If identical HP data are repeatedly recorded over 9 tracks (over 9
tracks within the range indicated by RP in FIG. 48), the HP data
can be read at five-time and nine-time speeds.
[0021] FIG. 49A and FIG. 49B show scanning traces at five-time
speed replay. In the illustrated example, identical HP data is
repeatedly recorded over five consecutive tracks (within the region
indicated by RP). As will be seen from the drawings, identical HP
data is recorded over the number of tracks identical to the number
of times of the tape speed (i.e., 5). In either of case 1 and case
2, either the head A or B can read HP data from corresponding
azimuth track. Accordingly, providing the copy areas in each track,
in a number identical to the number of times of the tape speed at
the fast replay, and repeatedly recording the HP data there, the
copied HP data can be read at various speeds, and in either the
forward or reverse direction.
[0022] In the manner described, the special replay data is recorded
in the copy areas, repeatedly, to improve the picture quality
during the special replay in the transparent recording system.
[0023] FIG. 50 shows a recording format on a track in a
conventional digital VTR. Main areas 270 and copy areas 271 are
provided in one track. In a consumer digital VTR, a video area in
each track has 135 sync blocks (SB), and 97 sync blocks are
assigned to main areas and 32 sync blocks are assigned to copy
areas. The sync blocks at the regions corresponding to the 4-, 9-
and 17-time speed shown in FIG. 47 are selected for the copy areas.
The data rate of the main areas is about 17.46 Mbps
(97.times.75.times.8.times.10.times.30), and the data rate of the
copy areas where identical data is repeated 17 times is about 338.8
kbps (32.times.75.times.8.times.10.times.30/17).
[0024] The convention VTR described above has the following
problems.
[0025] In the conventional VTR, in any of the cases of the
low-speed replay of 2- to 4 time speed, and the case of a fast
replay of more than 9-time speed, the data of the copy areas
consisting of the predetermined number of sync blocks contained in
a common overlapping areas is read and used for replay. As a
result, the deterioration in the picture quality which is not
conspicuous in a high-speed fast replay, in which the change of the
scene is quick, shows up in a lower-speed replay, in which the
change is of the scene is slow.
[0026] In the convention device, the areas where the copy areas
overlap are determined without taking account of the regions where
the reading is possible in slow replay or still replay. As a
result, when slow or still replay is conducted in the conventional
device, the reading from the copy areas is not necessary ensure.
Moreover, the picture is not reconstructed from only the HP data in
the copy areas, so that the pictures of slow or still replay are
not obtained.
[0027] When a bit stream from the main areas is used during slow or
still replay, some regions may not be scanned, or the replay output
may be insufficient, so that replay data is not obtained from some
regions. Thus, replay of data from all the areas is not ensured,
and slow or still replay pictures of good quality cannot be
obtained.
[0028] In the conventional device, where each transport packet is
divided and recorded in a plurality of sync blocks on the tape, the
positions at which the packet is divided and the number of sync
blocks into which the packet is divided are not constant because of
the image compression. That is, depending on the characteristics of
the picture, the amount of data contained may vary and the length
of each packet may vary. For this reason, when the transport packet
is divided and recorded in many sync blocks, it is affected easily
by data errors for each sync block associated with the magnetic
recording and replay.
[0029] More specifically, assume that a packet of a length of 188
bytes is divided and recorded in consecutive sync blocks of a
length of 77 bytes. Generally, the ratio between the length of the
packets and the length of the sync block is not an integer. The
number of sync blocks for each packet differs. The position at
which the packet is divided also varies, and accordingly, the
number of sync blocks into which the packet is divided varies
between 3 and 4.
[0030] When digital data is magnetically recorded or replayed, data
errors for each sync block occurs. If the data in the replayed
packet contains an error, it cannot be used. A packet which is
divided into four sync blocks has a higher probability of being
erroneous than a packet which is divided into three sync
blocks.
[0031] When data used for fast replay is used, by reducing the
amount of data from ordinary encoded data, no control is made to
maintain that the data of the image blocks is recorded at a
predetermined number of sync blocks. Accordingly, when data of
frame picture for high-speed replay is recorded in a plurality of
sync blocks on a magnetic tape, the encoded data of the image
blocks is divided at the boundaries between the sync blocks. As a
result, the blocks recorded being divided is easily affected by the
data errors for each sync block, associated with the magnetic
recording and replay.
[0032] When image block data of a 50 byte length is recorded, it
may be recorded within a single sync block, or it may be divided
into two sync blocks. In comparison with the case where recording
is in one sync block only, if the recording is into two sync
blocks, the effect of errors for each sync block associated with
recording and replay is twice.
[0033] Moreover, the positions at which the fast replay data is
recorded are determined on the basis of the head scanning traces at
a specific fast replay speed. As a result, fast replay is not
possible at speeds other than the specific fast replay speed.
[0034] Furthermore, the copy areas where the fast replay data is
recorded are disposed on the tracks such that reading from them can
be made correctly. However, slow replay is not taken account of, so
that it is not sure whether data is read correctly. Thus, the
conventional device does not have any assurance with regard to the
picture quality of slow replay.
[0035] Moreover, when still replay is selected, the replay data is
not read, and no still picture is correctly displayed.
[0036] Furthermore, with regard to the speed of the fast replay in
the conventional device, even where identical copy data is recorded
over 17 tracks, odd-number multiple-speeds which can be selected
are limited to +17-time speed, +13-time speed, +9-time speed,
+5-time speed, -15-time speed, -11-time speed, -7-time speed, and
-3-time speed.
[0037] In order to check all the intra-picture data, the headers of
the ATV bit steams must be analyzed for each macro block.
SUMMARY OF THE INVENTION
[0038] The invention has been achieved to solve the problems
described above, and its object is to provide a digital VTR with
which the picture quality is higher in low-speed fast reply, than
in middle- or high-speed fast replay.
[0039] Another object of the invention is to provide a digital VTR
which records a bit stream transmitted digitally, and with which
slow or still replay picture of a good quality can be obtained even
when slow or still replay is conducted.
[0040] Another object of the invention is to provide a digital VTR
which is less affected by data errors associated with recording and
replay.
[0041] A further object of the invention is to provide a digital
VTR with which a fast replay is possible at an arbitrary speed.
[0042] A further object of the invention is to provide a digital
VTR which records a bit stream transmitted digitally, and with
which slow or still replay pictures of a good quality are obtained
even if slow or still replay is conducted.
[0043] A further object of the invention is to provide a digital
VTR with which the number of multiple-speeds which can be selected
for fast replay can be increased, and intra-picture data can be
detected for each frame or each field.
[0044] According to a first aspect of the invention, there is
provided a digital VTR magnetically recording and replaying video
and audio signals at a recording data rate higher than a data rate
of a bit stream which is digitally transmitted, recording the bit
stream on a magnetic recording medium, by dividing the data for one
screen as a baseband video signal, into a plurality of tracks,
[0045] comprising:
[0046] data extracting means for dividing a first low-frequency
component data from intra-encoded blocks of the bit stream, into a
predetermined number L (L being a positive integer not smaller than
2) and extracting the divided low-frequency component, and
extracting a second low-frequency component data having frequencies
higher than the first low-frequency component data; and
[0047] recording means for recording the first low-frequency
component data, being divided, in said predetermined number L of
first specific regions respectively disposed in a plurality of
tracks into which data for said one screen is divided, and
recording said second low-frequency component data in second
specific regions disposed in specific tracks of said plurality of
tracks, and recording all the bit stream in the remaining regions
in each track, other than said first and second specific
regions.
[0048] With the above arrangement,
[0049] during normal replay, all the bit stream digitally
transmitted during recording can be replayed and used,
[0050] during middle-speed and high-speed fast replay, the first
low-frequency component recorded in the first specific regions is
replayed, and
[0051] during low-speed fast replay, the second low-frequency
component recorded in the second specific regions on the specific
tracks and the first low-frequency component recorded in the first
specific regions are replayed and used.
[0052] Accordingly, the first HP data D1 is recorded in the first
specific regions and the second HP data D2 is recorded in the
second specific regions in the specific tracks, within the range of
data rate not larger than the remaining data rate after subtracting
the date rate for recording the bit stream, so that it is possible
to cope not only with the normal replay, but also with low-speed
fast replay, and middle-speed and high-speed fast replay, in which
the pictures are formed only of intra-encoded blocks, and the
pictures of a better quality is obtained in the low-speed fast
replay than in the middle-speed and high-speed fast replay.
[0053] The digital VTR of the first aspect of the invention may
further comprise:
[0054] selecting means for selecting one of a normal replay and
fast replays of a plurality of speeds, by varying the transport
speed of the magnetic recording medium;
[0055] control means for causing, when the fast replay at a
low-speed is selected by said selecting means, the transport speed
of the magnetic recording medium to be periodically alternated
between a speed near the standard speed for the normal replay and a
speed near the speed for the low-speed fast replay; and
[0056] replay means for replaying, at the speed near the standard
speed, at least the second low-frequency component data recorded in
said specific regions from said specific tracks, and the first
low-frequency component data recorded in said first specific
regions in said specific tracks.
[0057] With the above arrangement,
[0058] in the middle-speed or high-speed fast replay, the magnetic
recording medium is made to run continuously at a middle-speed or
high-speed fast replay speed, so that the first low-frequency
component data is collected and replayed from a plurality of
tracks, and
[0059] in the low-speed fast replay, at least the second
low-frequency component recorded in the second specific regions in
the specific tracks which can be obtained during transport at a
speed near the normal replay speed, and the first low-frequency
component recorded in the first specific regions in the specific
tracks are replayed as fast replay data.
[0060] Accordingly, the bit stream digitally transmitted for
recording can all be replayed during normal replay, so that there
is no degradation in the picture quality. In the middle-speed and
high-speed fast replay, although the picture quality is lower than
in the normal replay, it is possible to cope with search of the
recorded contents, and the like.
[0061] Moreover, in a replay of a low speed, of about twice the
normal speed, the magnetic tape is alternately transported at a
speed near the standard speed for normal replay, and a speed near
the low-speed fast replay speed, and at the speed near the standard
speed, at least the second low-frequency component data recorded in
the second specific regions in the specific tracks, and the first
low-frequency component data recorded in the first specific regions
are all replayed, so that although the resolution of the
high-frequency region is lost, compared with the normal replay, the
pictures with a better quality than in the middle-speed and
high-speed fast replay can be obtained.
[0062] According to a second aspect of the invention, there is
provided a digital VTR for magnetically recording and replaying a
bit stream digitally transmitted, comprising:
[0063] detecting means for detecting intra-picture data in the bit
stream that are replayed;
[0064] extracting means for extracting the intra-picture data from
the replayed bit stream, according to the result of the detection
at the detecting means;
[0065] replay mode designating means for selecting and designating
one of the normal replay, slow replay and still replay, as a replay
mode; and
[0066] replay data outputting means for storing the extracted
intra-picture data, and outputting the intra-picture data as the
replay picture data, according to the mode signal output by said
replay mode designating signal.
[0067] With the above arrangement
[0068] during replay with a digital VTR for recording and replaying
a bit stream digitally transmitted, the intra-picture data in the
bit stream that is replayed is detected, and intra-picture data is
extracted from the replayed bit stream on the basis of the result
of the detection, and the intra-picture data is stored, and output
as the replay picture data according to the replay mode signal,
[0069] so that even when the replay mode is slow replay, or still
replay, the stored intra-picture data can be output as the replay
data, and slow or still replay pictures with a good quality can be
obtained.
[0070] In the digital VTR of the second aspect of the invention, it
may be so arranged that said replay data output means
comprises:
[0071] address detecting means for detecting an address of the
track at which the intra picture data is recorded;
[0072] control means for causing normal speed replay and rewinding,
for reverse control, on the basis of the result of the detection of
the address of the track.
[0073] With the above arrangement,
[0074] when the replay mode signal designates slow replay or still
replay, and the normal speed replay and rewinding are conducted
alternately for slow replay,
[0075] the intra-picture data in the bit stream during normal speed
replay is detected, and the intra-picture data is extracted from
the replayed bit stream on the basis of the result of the
detection, and the intra-picture data is stored, and the address of
the recording track where the intra picture data is recorded is
detected, and the reverse control is conducted on the basis of the
result of the detection, and the stored intra-picture data is
output as the replay picture data,
[0076] so that when the designated replay mode is slow replay or
still replay, the stored intra-picture data is output as the replay
data, and slow or still replay pictures of a good quality are
obtained.
[0077] Accordingly, the stored intra-picture data can be output as
the replay data, during slow or still replay, so that slow or still
replay pictures of a good quality can be obtained.
[0078] In the digital VTR of the second aspect of the invention,
said replay data output means may comprise:
[0079] control means for stopping the tape for a predetermined
period after all the intra-picture data is extracted from the bit
stream by normal speed replay.
[0080] With the above arrangement,
[0081] when normal speed replay and halting are conducted
intermittently, as replay mode signal indicates slow replay,
[0082] the intra-picture data in the bit stream during normal speed
replay is detected, and the intra-picture data is extracted from
the replayed bit stream, and stored, and after all the
intra-picture data is extracted, the tape is halted for a
predetermined period, and the stored intra-picture data is output
as the replay picture data,
[0083] so that when the designated replay mode is slow replay, the
intra-picture data is output as the replay data, whereby slow
replay pictures with a good quality are obtained.
[0084] According to a third aspect of the invention, there is
provided a digital VTR for magnetically recording and replaying
digitally transmitted bit stream in a predetermined recording
format, a magnetic recording and replaying device comprising:
[0085] division number setting means responsive to a bit stream
input, a predetermined number M (M being a positive integer) of
transport packets as a unit, for setting the division number N (N
being a positive integer, N.noteq.M) into sync blocks which are to
form the recording format;
[0086] header appending means for appending, to data of the bit
stream before the division, a header indicating the transport
packet; and
[0087] format forming means for forming N consecutive sync blocks
from the data after the division of the bit stream.
[0088] With the above arrangement,
[0089] the predetermined number M of packet data are divided into
and recorded in the predetermined number N of the sync blocks. For
instance, when the size of the packet is 188 bytes, and the data
capacity of the sync block is 77 bytes, 376 bytes, which is twice
188 bytes, is smaller than 376 bytes, which is five times 77 bytes,
so that M is set to 2 and N is set to 5, and two packets are
recorded in five sync blocks. There are four boundaries between
five consecutive sync blocks, and each of the packet data extends
across the boundaries at two locations, and not at three or more
locations.
[0090] Accordingly, when transparent recording is effected, the the
number of units into which the packets of the bit stream is divided
can be made small on average, and the probability of the entire
packet being rendered erroneous because of the data error due to
recording and replay can be minimized.
[0091] According to fourth aspect of the invention, there is
provided a digital VTR for magnetically recording and replaying a
digitally transmitted bit stream in a predetermined recording
format, comprising:
[0092] decoding means for decoding the content of data of an input
bit stream;
[0093] data extracting means for extracting a series of encoded
data used for fast replay, on the basis of the decoded data;
and
[0094] data reducing means for reducing the data amount of the
extracted encoded data to a data amount which can be recorded in K
sync blocks (K being a positive integer) in said predetermined
format.
[0095] With the above arrangement,
[0096] when encoded data used for fast replay is formed from
original data, by reducing the data amount,
[0097] the data amount after the reduction is of such a size which
can be recorded in a predetermined number of sync blocks, and the
data is recorded in the predetermined number of sync blocks.
[0098] Accordingly, the number of units into which block data is
divided when the fast replay data is recorded on the tape can be
minimized on average, so that the probability of the entire block
data being erroneous because of data error due to recording and
replay can be minimized.
[0099] In the digital VTR of the fourth aspect of the invention, it
may be so arranged that said encoded data is recorded repeatedly
for a number of times about twice the multiplier of the maximum
fast replay speed (maximum speed at which the fast replay is
possible).
[0100] With the above arrangement,
[0101] the encoded data for fast replay is recorded repeatedly on
consecutive tracks a number of times which is about twice the
multiplier of the fast replay speed,
[0102] so that either of the heads of the different azimuths scans
the recording regions of the encoded data for fast replay at least
once, even when the replay is made with the maximum speed at which
replay is possible.
[0103] If the heads on the drum are disposed in opposition,
180.degree. apart, the tape is wrapped around the drum over about
180.degree., and the speed of the maximum fast replay is an even
multiple speed, the first and second azimuth heads supplement, each
other, the data that cannot be replayed by each of the heads,
alone.
[0104] All the replay encoded data can be reproduced, and the fast
replay can be conducted at any arbitrary even multiple speed. The
fast replay in a reverse direction is also possible, at any
arbitrary even multiple speed.
[0105] According to a fifth aspect of the invention, there is
provided a digital VTR for magnetically recording and replaying a
digitally transmitted bit stream, comprising:
[0106] detecting means for detecting intra-picture data in an input
bit stream;
[0107] forming means for forming fast replay data from the
intra-picture data;
[0108] header appending means for appending a first header for
discriminating the fast replay data from normal replay data, and a
second header for discriminating, within said normal replay data,
the intra-picture data and non-intra-picture data from each other,
and
[0109] recording means for recording the fast replay data together
with the normal replay data on a magnetic recording medium.
[0110] With the above arrangement,
[0111] in a device for recording and replaying a digitally
transmitted bit stream,
[0112] at the time of recording, intra-picture data is detected
from the input bit stream, and fast replay data is formed, and a
first header for discriminating the normal replay data and the fast
replay data from each other, a second header for discriminating,
within the normal replay data, the intra-picture data and
non-intra-picture data from each other, are appended before
recording. Accordingly, during normal replay, normal replay data is
selected from the data having been read, according to the first
header, and output.
[0113] The data output respectively for normal replay and fast
replay, can therefore be smoothly selected.
[0114] The digital VTR of the fifth aspect of the invention may
further comprise:
[0115] replay means for replaying normal replay data, together with
fast replay data from the magnetic recording medium;
[0116] separating means for separating the normal replay data, by
checking the first header appended to the replay data from the
magnetic recording medium;
[0117] storage means for storing the intra-picture data, by
checking the second header appended to the normal replay data
selected by the separating means; and
[0118] switching means for selectively outputting the normal replay
data or the intra-picture data stored in the storage means,
depending on whether the replay mode is the normal replay or the
still replay.
[0119] With the above arrangement,
[0120] the normal replay data is selected and separated from the
data having been read during normal replay, according to the first
header,
[0121] only the intra-picture data is extracted from the normal
replay data according to the second header, and stored,
[0122] so that, during still replay, the normal replay data is
selected and output from the storage means. As a result,
satisfactory still replay can be achieved.
[0123] The second headers for discriminating between the
intra-picture data and non-intra-picture data are appended to the
transport packets which are normal replay data before recording, so
that the detection of the intra-picture data during still replay is
facilitated.
[0124] Moreover, the intra-picture data detected according to the
second header during normal replay is stored, and output when still
replay is selected, so that switching to the still replay mode is
achieved with ease.
[0125] The digital VTR of the fifth aspect of the invention may
further comprise:
[0126] replay means for replaying normal replay data together with
the fast replay data from the magnetic recording medium;
[0127] separating means for separating the normal replay data, by
checking the first header appended to the replay data from the
magnetic recording medium;
[0128] storage means for storing the intra-picture data, by
checking the second header appended to the normal replay data
selected by said separating means; and
[0129] switching means for selectively outputting the normal replay
data or the intra-picture data stored in the storage means,
depending on whether the replay mode is the normal replay or the
slow replay.
[0130] With the above arrangement,
[0131] during slow replay, the normal replay data is selected and
separated according to the first header, and
[0132] only the intra-picture data is extracted from the normal
replay data according to the second header,
[0133] so that, by selectively outputting the normal replay data
from the storage means, satisfactory low-speed replay can be
achieved.
[0134] The intra-picture data detected according to the second
header is recorded during slow replay, and intra-picture data is
selected and output, so that slow replay can be achieved with
ease.
[0135] Moreover, the transport packets which are the normal replay
data are recorded, after having appended second headers for
discriminating the intra-picture data and non-intra-picture data
from each other, so that, during slow replay, detection of the
intra-picture data is achieved with ease.
[0136] The digital VTR of the fifth aspect of the invention may
further comprise:
[0137] replay means for replaying normal replay data together with
the fast replay data from the magnetic recording medium;
[0138] separating means for separating the fast replay data from
the normal replay data, by checking the first header appended to
the replay data from the magnetic recording medium; and
[0139] switching means for selectively outputting the normal replay
data or the high-speed data, depending on whether the replay mode
is the normal replay or the fast replay.
[0140] With the above arrangement,
[0141] during fast replay, the fast replay data can be selected and
output with ease, from the data having been read, according to the
second header.
[0142] Because the first header for discriminating the transport
packets with which normal replay is possible, and fast replay data
from each other, selection of the data output respectively during
normal replay and fast replay can be made smoothly.
[0143] According to a sixth aspect of the invention, there is
provided a digital VTR for magnetically recording and replaying a
digitally transmitted bit stream, comprising:
[0144] means for forming HP data for fast replay, by extracting
low-frequency component from intra-encoded data of an input bit
stream;
[0145] pattern generating means for forming a recording pattern for
recording the HP data, being divided, and a plurality of times, in
copy areas respectively set in J tracks (J=12.times.I+5, I being a
positive integer) forming one track group; and
[0146] recording means for recording in the formats according to
the recording patterns, partitioning one track into a main area in
which only said bit stream is recorded, and a plurality of copy
areas in which said HP data is recorded, being divided;
[0147] wherein the recording patterns of the HP data A, B and C
recorded, being divided into the N tracks include
[0148] a pattern TP1 in which HP data B is recorded in the copy
area at the center of the track, and HP data A is recorded in the
copy areas at both ends of the track,
[0149] a pattern TP2 in which HP data A is recorded in the copy
area at the center of the track, and HP data C is recorded in the
copy areas at both ends of the track,
[0150] a pattern TP3 in which HP data A is recorded in the copy
areas at the center and both ends of the track,
[0151] a pattern TP4 in which HP data C is recorded in the copy
area at the center of the track, and HP data A is recorded in the
copy areas at both ends of the track,
[0152] a pattern TP5 in which HP data B is recorded in the copy
area at the center of the track, and HP data C is recorded in the
copy areas at both ends of the track, and
[0153] a pattern TP6 in which HP data B is recorded in the copy
areas at the center and both ends of the track, and
[0154] in one track group,
[0155] a first track of pattern TP4 is disposed in the center of
the track group,
[0156] a second track of pattern TP1 is disposed at one end of the
track group,
[0157] a third track of pattern TP6 is disposed at the opposite end
of the track group,
[0158] tracks of patterns TP2 and TP3 are alternately and
repeatedly disposed between the first track and the second
track,
[0159] tracks of patterns TP5 and TP6 are alternately and
repeatedly disposed between the first track and the third
track.
[0160] With the above arrangement, when 1 track group is formed of
17 tracks, the recording format permits the multiplier of the fast
replay speed to be, in addition to +17, +13, +9, +5, -15, -11, -7,
and -3, as in prior art, 3, 7, -5, and -1.
[0161] It is thus possible to form a recording format by which, by
disposing the HP data, the number of multiple-speeds which can be
selected for the fast replay can be increased.
[0162] According to a seventh aspect of the invention, there is
provided a digital VTR for magnetically recording and replaying a
digitally transmitted bit stream, comprising:
[0163] means for forming HP data for fast replay, by extracting
low-frequency component from intra-encoded data of an input bit
stream;
[0164] pattern generating means for forming a recording pattern for
recording the HP data, being divided, and a plurality of times, in
copy areas respectively set in J tracks (J=12.times.I+5, I being a
positive integer) forming one track group; and
[0165] recording means for recording in the formats according to
the recording patterns, partitioning one track into a main area in
which only said bit stream is recorded, and a plurality of copy
areas in which said HP data is recorded, being divided;
[0166] wherein the recording patterns of the HP data A, B and C
recorded, being divided into the N tracks include
[0167] a pattern TP1 in which HP data B is recorded in the copy
area at the center of the track, and HP data A is recorded in the
copy areas at both ends of the track,
[0168] a pattern TP2 in which HP data A is recorded in the copy
area at the center of the track, and HP data B is recorded in the
copy areas at both ends of the track,
[0169] a pattern TP3 in which HP data A is recorded in the copy
areas at the center and both ends of the track,
[0170] a pattern TP4 in which HP data A is recorded in the copy
area at the center of the track, and HP data C is recorded in the
copy areas at both ends of the track,
[0171] a pattern TP5 in which HP data C is recorded in the copy
area at the center of the track, and HP data A is recorded in the
copy areas at both ends of the track,
[0172] a pattern TP6 in which HP data C is recorded in the copy
areas at the center and both ends of the track,
[0173] a pattern TP7 in which HP data C is recorded in the copy
area at the center of the track, and HP data B is recorded in the
copy areas at both ends of the track,
[0174] a pattern TP8 in which HP data B is recorded in the copy
area at the center of the track, and HP data C is recorded in the
copy areas at both ends of the track, and
[0175] a pattern TP9 in which HP data B is recorded in the copy
areas at the center and both ends of the track, and
[0176] in one track group,
[0177] a first track of pattern TP5 is disposed in the center of
the track group,
[0178] second and third tracks of pattern TP6 are disposed on both
sides of and adjacent to the first track of pattern TP5,
[0179] a fourth track of pattern TP5 is disposed adjacent the
second track of pattern TP6,
[0180] a fifth track of pattern TP7 is disposed adjacent the third
track, and on the opposite side of the fourth track of pattern TP5,
with respect to the first track,
[0181] a sixth track of pattern TP1 is disposed at the head or tail
of the track group, and on the same side of the first track as the
fourth track,
[0182] a seventh track of pattern TP2 is disposed next to the track
of pattern TP1, and on the same side of the first track as the
fourth track,
[0183] an eighth track of pattern TP9 is disposed at the tail or
head of the track group, and on the same side of the first track as
the fifth track,
[0184] tracks of patterns TP3 and TP4 are alternately and
repeatedly disposed between the seventh track and the fourth
track,
[0185] tracks of patterns TP8 and TP9 are alternately and
repeatedly disposed between the eighth track and the fifth
track.
[0186] With the above arrangement,
[0187] when 1 track group is formed of 17 tracks, the recording
format permits the multiplier of the fast replay speed to be, in
addition to +17, +13, +9, +5, -15, -11, -7, and -3, as in prior
art, 3, 7, -5, and -1.
[0188] It is thus possible to form a recording format by which, by
disposing the HP data, the number of multiple-speeds which can be
selected for the fast replay can be increased.
[0189] In either of the sixth and seventh aspects of the invention,
it may be so arranged that, in normal replay, the bit stream
recorded in the main area is transmitted to a decoder as a replay
signal, and, in fast replay, a replay bit stream is formed from the
HP data, and transmitted to the decoder as replay HP data.
[0190] With the above arrangement, when 1 track group is formed of
17 tracks, it is possible to perform replay at the speeds of
+17-time, +13-time, +9-time, +5-time, -15-time, -11-time, -7-time,
and -3-time, as in prior art, and, in addition, 3-time, 7-time,
-5-time, and -1-time.
[0191] It is thus possible to increase the number of
multiple-speeds which can be selected for fast replay from a format
used for recording with the digital VTR.
[0192] In either of the sixth or seventh aspects of the invention,
it may be so arranged that, wherein the intra-encoded blocks
forming the HP data belong to intra-encoded frame or intra-encoded
field.
[0193] With the above arrangement, detection of the intra-picture
data which forms the basis for forming the HP data recorded in the
copy areas is simplified.
BRIEF DESCRIPTION OF THE DRAWINGS
[0194] In the accompanying drawings:
[0195] FIG. 1 is a block diagram showing a recording system of a
digital VTR of Embodiment 1 of the invention;
[0196] FIG. 2 is a diagram showing a sync block forming a recording
block;
[0197] FIG. 3 is a diagram showing a track format of recording data
according to Embodiment 1;
[0198] FIG. 4 is a block diagram showing a replay system of a
digital VTR of Embodiment 1 of the invention;
[0199] FIG. 5 is a diagram showing the state of transport of a
magnetic tape in low-speed fast replay;
[0200] FIG. 6 is a diagram showing the scanning trace of a head
against a specific track in a low-speed fast replay;
[0201] FIG. 7A to FIG. 7D are diagrams for explaining the memory
control operation in the low-speed fast replay;
[0202] FIG. 8 is a diagram showing the scanning trace of a head
against a specific track in a middle-speed or high-speed
replay;
[0203] FIG. 9 is a block diagram showing a replay system of a
digital VTR of Embodiment 2 of the invention;
[0204] FIG. 10 is a diagram for explaining the control operation in
slow replay;
[0205] FIG. 11 is a schematic diagram showing a GOP forming an
MPEG2 bit stream;
[0206] FIG. 12 is a diagram showing the relationship between the
tape transport speed and the period when the intra-picture data is
picked up, in Embodiment 2;
[0207] FIG. 13A and FIG. 13B are diagrams for explaining the
control operation in reverse slow replay in Embodiment 3;
[0208] FIG. 14 is a block diagram showing a replay system of a
digital VTR of Embodiment 4 of the invention;
[0209] FIG. 15 is a diagram for explaining the control operation in
slow replay;
[0210] FIG. 16 is a diagram showing the relationship between the
tape transport speed and the period when the intra-picture data is
picked up, in Embodiment 4;
[0211] FIG. 17 is a block diagram showing a recording system of a
digital VTR of Embodiment 5 of the invention;
[0212] FIG. 18A shows the encoded data and decoded data of the
image block, for explaining the decoding of the image block in a
recording system;
[0213] FIG. 18B shows the configuration of the HP data for
high-speed replay, for explaining the decoding of the image block
in the recording system;
[0214] FIG. 19 is a flow chart showing the procedure of the
decoding of the image block in the recording system;
[0215] FIG. 20 is a diagram showing a recording pattern of the
high-speed replay data;
[0216] FIG. 21 is a diagram showing a packet recording pattern;
[0217] FIG. 22 is a diagram showing a recording track on a magnetic
tape;
[0218] FIG. 23 is a block diagram showing a replay system of a
digital VTR of Embodiment 5;
[0219] FIG. 24 is a diagram showing a track format and a head
scanning pattern that result when double speed replay is conducted
from a recorded tape;
[0220] FIG. 25 is a diagram showing a track and a head scanning
pattern that result when four-time speed replay is conducted from a
recorded tape;
[0221] FIG. 26A and FIG. 26B are diagrams showing the signal level
obtained when replayed by two different heads of different widths,
and the track regions where data is reproduced, in the track
pattern of FIG. 25;
[0222] FIG. 27 is block diagram showing a recording system of a
digital VTR of Embodiment 6 of the invention;
[0223] FIG. 28 is a diagram showing the data track format in the
video area of a digital VTR;
[0224] FIG. 29 is a diagram showing the configuration of a
transport packet contained in the bit stream;
[0225] FIG. 30 is a diagram showing the configuration of data of
the main areas recorded on the magnetic tape;
[0226] FIG. 31 is a diagram showing the data configuration of the
copy areas;
[0227] FIG. 32 is a block diagram showing a replay system of a
digital VTR of Embodiment 6;
[0228] FIG. 33 is a block diagram showing a recording system of a
digital VTR of Embodiment 7 of the invention;
[0229] FIG. 34 is a diagram showing the recording pattern of HP
data recorded on the tracks;
[0230] FIG. 35 is a diagram showing the pattern signal generated by
the pattern signal generator;
[0231] FIG. 36 is a diagram showing the data configuration of a
sync block;
[0232] FIG. 37 is a diagram showing the data configuration of a
sync block;
[0233] FIG. 38 is a diagram showing a recording pattern of HP data
recorded on the tracks in Embodiment 8;
[0234] FIG. 39A and FIG. 39B are diagrams showing an example of
replay system of a digital VTR in Embodiment 8;
[0235] FIG. 40 is a diagram showing scanning traces of a rotary
head during the seven-time speed replay;
[0236] FIG. 41 is a diagram showing a track pattern of a
conventional consumer digital VTR;
[0237] FIG. 42A shows scanning traces against tracks formed on the
magnetic tape in normal replay in a conventional digital VTR;
[0238] FIG. 42B shows scanning traces against tracks in a fast
replay in the conventional digital VTR;
[0239] FIG. 43 is a block diagram showing an example of recording
system of a conventional digital VTR capable of fast replay;
[0240] FIG. 44 is a diagram showing an example of data format of
data recorded on the tracks in the prior art;
[0241] FIG. 45A is a schematic diagram showing normal replay in an
example of a replay system of a conventional digital VTR;
[0242] FIG. 45B is a schematic diagram showing fast replay in the
example of a replay system of the conventional digital VTR;
[0243] FIG. 46A is a diagram showing a scanning trace in a fast
replay;
[0244] FIG. 46B is a diagram showing track regions where fast
replay is possible;
[0245] FIG. 47 is a diagram showing regions of the copy areas
between different fast replay speeds;
[0246] FIG. 48 is a diagram showing examples of scanning traces of
a rotary head of different tape speeds;
[0247] FIG. 49A and FIG. 49B are diagrams showing the scanning
traces of a rotary head in five-time speed replay; and
[0248] FIG. 50 is a diagram showing scanning traces showing
recording format on the tracks of a conventional digital VTR.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
EMBODIMENT 1
[0249] Embodiment 1 is for obtaining a replay picture with a good
picture quality, in particular at the time of low-speed fast
replay.
[0250] FIG. 1 is a block diagram showing a recording system of a
digital VTR of and embodiment of the invention. In the drawing,
reference numeral 1 denotes a bit stream input terminal, 4 denotes
a variable-length decoder, 5 denotes a counter, 6 denotes a data
extracting circuit, 7 denotes an EOB (end of block) appending
circuit, 10 denotes an error correction encoder, 11 denotes a
recording signal processing circuit comprising a modulating circuit
and a recording amplifier, and 15 denotes a magnetic head.
[0251] An MPEG2 bit stream is input via the input terminal 1 to the
error correction encoder 10, where error correction codes used
during normal replay are appended, and sync signals and ID
information are also appended. The error correction codes used
during normal replay consist for example of a product code
configuration, consisting of inner error correcting codes and outer
error correcting codes.
[0252] The bit stream via the input terminal 1 is also input to the
variable-length decoder 4, where the syntax of the MPEG2 bit stream
is analyzed, and variable-length encoded intra-picture data is
detected, and the number of the data units is counted at the
counter 5. The counter 5 provides the data extracting circuit 6
with timing signals for commencing and terminating extraction of
intra-encoded blocks. The data extracting circuit 6 extracts all
the intra-encoded blocks forming the intra-picture data, and
extracts the low-frequency components of the intra-encoded blocks,
in order to reduce the data. That is, the data extracting circuit 6
applies DCT processing to the blocks of 8.times.8 pixel
configuration in the intra-picture data, and extracts the
low-frequency component data of the DCT coefficients, consisting DC
components and low-frequency AC components in the horizontal and
vertical spatial frequency regions of the DCT coefficients.
[0253] The low-frequency component data extracted from the
intra-picture data is the important part (hereinafter referred to
as HP data) of the bit stream used for the reconstruction of the
picture at the time of fast or multiple-speed replay. At the time
of extraction, the HP data is divided into two units of two special
replay data, i.e., first HP data D1 and second HP data D2, and
output via the data extracting circuit 6. The division is so made
that the first and second HP data D1 and D2 respectively contain
first and second low-frequency components, and the second HP data
D2 contains AC components having higher frequencies than the first
HP data D1. The EOBs are appended at the EOB appending circuit 7 to
the first and second HP data D1 and D2, and the first and second HP
data D1 and D2 with the EOBs appended is input to the error
correction encoder 10, as data for recording in the copy areas, and
error correction codes, sync signals and ID information which are
used in fast replay are appended to form recording blocks. The
error correction codes of the recording blocks used during fast
replay are of inner codes configuration.
[0254] The recording signal processing circuit 11 modulates the
recording blocks for the main and copy areas output from the error
correction encoder 10, and records via the magnetic head 15 on a
magnetic recording medium, such as a magnetic tape (not shown).
[0255] FIG. 2 shows sync blocks forming the recording blocks. In
the drawing, reference numeral 20 denotes a region for recording a
sync signal, 21 denotes a region for recording ID information
(identification information), such as recorded track address
information, 22 denotes a region for recording the data regarding
the bit stream for the main areas, or the first and second HP data
for the copy areas, and 23 denotes a region for recording error
correction codes which are inner codes appended to the sync
blocks.
[0256] FIG. 3 shows a track format of the recording data of
Embodiment 1. In the drawing, each of reference marks A and B
denotes the type of the track corresponding to the respective
azimuth, and the tracks are helical. That is, each track is
helical-recorded alternately on the magnetic tape using heads of
different azimuths. The regions denoted by marks 1D1, 2D1, 3D1 are
first specific regions where sync blocks for the first HP data D1
for the copy areas are recorded.
[0257] The first HP data is divided into and recorded in the first
specific regions 1D1 to 3D1, at three specific locations on one
track. An example of the division is such that ten sync blocks
(hereinafter referred to as SBs) are allotted to the region 1D1,
eight SBs are allotted to the region 2D1, and seven SBs are
allotted to the region 3D1. The SBs allotted to the regions 1D1 to
3D1 correspond to the overlapping regions commonly head-traced at
various fast replays like in the prior art example, and SBs of 1D1
to 3D1 of the same content are repeatedly recorded over the number
of tracks identical to the speed multiplier of the highest-speed
replay speed. The term "multiplier" is used to mean the ratio of
the fast replay speed to the normal replay speed. This has already
been described in detail in connection with the prior art example,
so its further description is omitted here. In this embodiment,
however, the first HP data contained in the SBs of the regions 1D1
to 3D1 are used only at a middle-speed fast replay, around 9-time
speed, or of a higher-speed fast replay.
[0258] In FIG. 3, SBs for the second HP data D2 for the copy areas
are disposed in the second specific region 1D2 which is indicated
by hatching. This second specific region 1D2 is positioned on a
specific track, e.g., the first track TA, within ten recording
tracks for one frame (where the field frequency is 60 Hz) as a
baseband video signal which is a basic specification for a consumer
digital VTR. In the example under consideration, 1D2 is formed of
50 SBs, and contains much more intra-picture data than 1D1 to 3D1,
which contain 25 SBs in total. In this embodiment, this region 1D2
is used for a low-speed fast replay, of for example around
double-speed. In this specific track TA, 50 SBs for 1D2 and 25 SBs
for 1D1 to 3D1 are disposed. In the tracks other than the specific
track TA, 25 SBs for 1D1 to 3D1 are disposed as copy areas.
[0259] In the remaining regions, other than the first specific
regions in each track in FIG. 3, and the remaining regions other
than the first and second specific regions, are the main areas,
where all the SBs regarding the MPEG2 bit stream are recorded, and
replayed during normal replay. In consumer digital VTRs, the video
area on each track is formed of 135 SBs, so that the number of SBs
for the bit stream in the main areas in the specific track TA is 60
(=135-75), and is 110 (=135-25) in the tracks other than the
specific track TA.
[0260] As described above with reference to FIG. 41 in connection
with the prior art example, in a consumer digital VTR, data areas
such as audio areas, not shown, are provided on the extensions of
the video areas in each track, and the 135 SBs do not occupy all
the area of in the tape width direction. But FIG. 3 shows only the
video areas.
[0261] FIG. 4 is a block diagram showing the replay system of a
digital VTR which is an example of the invention. In the drawing,
reference numeral 15 denotes a replay magnetic head, 12 denotes a
replay signal processing circuit comprising a head amplifier and
having functions of detection and demodulation of the replay
signals, 13 denotes an error correction decoder correcting the
errors in the replay signal on the basis of the error correction
inner codes appended for each SB at the time of recording, and 14
denotes a memory having a capacity of constructing a picture (whole
frame) at the time of fast replay, by collecting only the first and
second HP data, or the first HP data only, from the copy areas.
Reference numeral 30 denotes an output terminal for low-speed fast
data, 32 denotes an output terminal for normal replay data, 40
denotes a capstan motor, 41 denotes a capstan control circuit, 42
denotes a system control circuit for switching between modes such
as normal replay mode, low-speed fast replay mode, and high-speed
fast replay mode, and 43 denotes a memory control circuit.
[0262] Description is now made of the operation of the fast replay
at a low-speed, around a double speed, for example. FIG. 5 shows
the scanning of tape transport at the time of the low-speed fast
replay. FIG. 6 shows the scanning trace of the head against a
magnetic tape during a low-speed fast replay. Responsive to a mode
signal designating a low-speed fast replay from the system control
circuit 42, the capstan control circuit 41 causes the capstan motor
40 to rotates in accordance with the tape speed control curve shown
in FIG. 5. That is, the tape transport speed is switched
periodically at a certain interval, between a speed which is a
little higher than and near the standard speed which is the normal
replay speed, and a high speed, e.g., about three-time speed. In
the period (t0 to t1) for the speed a little higher than the
standard speed, tracking is so made along the specific track TA as
shown in FIG. 6, to replay all the SBs including the 50 SBs for
1D2, 10 SBs for the 1D1, 8 SBs for 2D1 and 7 SBs for 3D1. In the
fast replay of around the double speed, fast replay data LP(n)
consisting of 75 SBs are output via the output terminal 30.
[0263] FIG. 7A to FIG. 7D are diagrams showing the memory control
operation during the low-speed fast replay. FIG. 7A and FIG. 7B
show the contents of the input data written in the memory 14, and
the control signal WE. FIG. 7C shows the content of the output data
read from the memory 14, and FIG. 7D shows the time axis.
[0264] The data of 75 SBs replayed during low-speed fast replay,
are error-correction processed at the error correction decoder 13
using the error correction inner codes, and flag information FC
indicating whether the error is correctable or uncorrectable is
output to the memory control circuit 43. Input to the memory
control circuit 43 from the capstan control circuit 41 is a speed
control information SC indicating the period (t0 to t1) for the
speed a little higher than the standard speed, and during such
period, the control signal WE is provided so that only the SBs
error-corrected at the error correction decoder 13, and so
indicated by the flag information FC are written in the memory 14.
The memory control circuit 43 supplies the memory 14 with a control
signal SE for continuously reading the previous fast data LP(n),
until the next period (t2 to t3) of a speed of a little higher than
the standard speed, shown in FIG. 5, when fast replay data LP (n+1)
of 75 SBs in total regarding 1D2, 1D1, 2D1 and 3D1 on the next
specific track TA is replayed.
[0265] By repeating the above operation, during the low-speed fast
replay, the low-frequency component data which are important part
in the bit stream for reconstructing the picture during low-speed
replay is read from the memory 14 as the first and second HP data
D1 and D2, and output via the output terminal 2, and supplied to
the MPEG2 decoder, not shown, and external to the digital VTR.
[0266] Next, description is made of the operation of the
middle-speed replay, of for example around 9 time-speed.
[0267] FIG. 8 shows the scanning traces of the head against the
specific tracks in the middle-speed or higher-speed fast replay.
Responsive to the mode signal for middle-speed fast replay from the
system control circuit 42, the capstan control circuit 41 causes
the magnetic tape to be transported at a speed around nine times
the standard speed. As in the nine-time speed in FIG. 48 of the
prior art example, the magnetic head 14 picks up 1D1, 2D1, 3D1 for
the first HP data, from the overlapping regions traced commonly at
various fast replay speeds, over a plurality of tracks, so that 25
SBs in total are reproduced.
[0268] The 25 SB data replayed during the middle-speed replay is
error-correction processed at the error correction decoder 13 using
the error correction inner codes, and flag information FC
indicating whether the data is correctable or uncorrectable is
output to the memory control circuit 43. During the middle-speed
replay, the magnetic tape is transported continuously at a speed
around nine times the normal speed, so that the speed control
information SC input to the memory control circuit 43 is
disregarded, and only the middle-speed fast replay data LP(n)
consisting of SBs having been error-corrected at the error
correction decoder 13 and so indicated by the flag information FC
(i.e., correctable SBs) is written in the memory 14. The data LP(n)
is continuously read until the next middle-speed replay data
LP(n+1) is replayed and written in the memory 14. The first HP data
D1 as the low-frequency component data which is an important part
of the bit stream for reconstructing a picture of a fast replay is
output via the output terminal 31, and sent to an MPEG decoder not
shown and external to the digital VTR.
[0269] The operation during fast replay at a speed higher than
nine-time speed is identical to that described above, so its
description is omitted.
[0270] The operation during normal replay is next described
briefly. In FIG. 3, during the normal relay, all the SBs for the
MPEG2 bit stream in the main areas which are the remaining regions
of the respective tracks are replayed. The replay data is
error-corrected at the error correction decoder 13 using the inner
codes and the outer codes, or amended (for concealment), and is
output via the output terminal 32, and sent to the MPEG2 decoder
not shown and external to the digital VTR.
[0271] In the above description, the first one of the ten tracks
for one frame period (where the field frequency is 60 Hz) is
assigned to the specific track TA, as shown in FIG. 3. However, any
other one of the ten tracks may be assigned to the specific track,
or two or more of the ten tracks may be assigned to specific
tracks. In the latter case, the specific tracks may be adjacent to
each other or separated from each other.
[0272] In the above description, 50 SBs forming the second HP data
D2 are disposed collectively in the second specific region on a
specific track. The 50 SBs forming the second HP data may be
divided into units of smaller numbers of SBs, and disposed at
different positions on the specific tracks.
[0273] In the low-speed fast replay, the entire specific track TA
is generally head-traced as shown in FIG. 6, so that the
intra-encoded sync blocks in the MPEG2 bit stream recorded in the
remaining regions on the specific track TA can also be used. In
that case, more intra-encoded data can be used than in the case
described above, so that the picture of the lower-speed fast replay
is further improved.
EMBODIMENT 2
[0274] Embodiments 2, 3 and 4 described next are for obtaining the
slow- and still-replay pictures of a good quality in a bit stream
recording and replay device, such as a digital VTR.
[0275] Embodiment 2 is for implementing slow replay by means of a
pre-roll method in which the replay system alternately conducts
normal speed replay and rewinding.
[0276] FIG. 9 is a block diagram showing the replay system of a
digital VTR in Embodiment 2. In the figure, reference numeral 58
denotes an input terminal for inputting replay signals read by the
head from the main areas and copy areas of the tape, 59 denotes a
replay signal processing circuit for performing processing such as
waveform equalization, signal detection and modulation, and
outputting the bit stream of the ATV signal, and the HP data, 60
denotes a data separation circuit for separating the input data
into the bit stream from the main areas and the HP data from the
copy areas, and 61 denotes a track address identifying circuit for
identifying the track address track replayed from the replay signal
from the replay signal processing circuit 59, and outputting a
signal indicative of the track number. Reference numeral 62 denotes
a replay mode signal generator for generating a signal indicative
of the replay mode of the respective one of the normal replay, fast
replay, slow replay and still replay, 63 denotes a control circuit
for generating control signals, such as the ones for controlling
the tape transport during slow replay and still replay, and 64
denotes an output terminal for outputting the control signals from
the control circuit 63 to the servo circuit.
[0277] Reference numeral 65 denotes a syntax analyzer for analyzing
the syntax of the MPEG2 bit stream from the main areas and
detecting intra-picture data, 66 denotes a counter, 67 denotes a
data extractor for extracting, storing and outputting intra-picture
data from the bit stream, 68 denotes a selector for selecting the
data according to the replay mode signal from the replay mode
signal generator 62, and 69 denotes an output terminal for
outputting the selected data to the MPEG2 decoder, provided outside
the digital VTR.
[0278] The replay operation of the digital VTR of Embodiment 2 will
next be described in detail. During normal replay and fast replay,
the replay signal read by the head from the tape is input via the
input terminal 58, and sent to the replay signal processing circuit
59, where waveform equalization, signal detection and demodulation
are performed, and output as the original ATV signal in the form of
a bit stream and the HP data. The data separation circuit 60
separates the replay data from the replay signal processing circuit
59 into the bit stream from the main areas and the HP data from the
copy areas. The bit stream from the main areas is output as the
normal replay data, and the HP data from the copy areas is
collected and output as the fast replay data, and they are supplied
to the selector 68. The the selector 68 selects, on the basis of
the replay mode signal from the replay mode signal generator 62,
the normal replay data in the form of the bit stream from the main
areas during normal replay, and the fast replay data in the form of
the HP data from the copy areas during fast replay. The selected
data is output via the output terminal 69 to the decoder, not
shown.
[0279] The operation during slow replay in Embodiment 2 will next
be described.
[0280] FIG. 10 shows the control operation in the slow replay. It
is assumed that the slow replay is achieved by a pre-roll method in
which normal speed replay and rewinding are alternately conducted.
In the normal speed replay during slow replay, the replay signal
read by the head from the tape is input via the input terminal 58,
and sent to the replay signal processing circuit 59, where replay
signal processings, such as waveform equalization, signal detection
and demodulation, are applied, and output as the bit stream forming
the original ATV signal and the HP data. At the data separation
circuit 60, the replay data is separated into the bit stream from
the main areas and the HP data from the copy areas, and the bit
stream from the main areas is output as the normal replay data, and
the HP data from the copy areas is collected and output as fast
replay data. The replay data from the replay signal processing
circuit 59 is sent to the track address identifying circuit 61, and
the data indicating the address of the track from which the replay
data is replayed, and the signal indicative of the track number is
output and input to the control circuit 63.
[0281] The bit stream from the main areas, forming the normal
replay data, output from the data separation circuit 60 is input to
the syntax analyzer 65, where the intra-picture data in the bit
stream is detected, and timing signals are generated by the counter
66, and the intra-picture data is extracted by the data extractor
67. The counter 66 generates a timing signal Sa indicating that an
intra-picture data has been extracted, and supplies the timing
signal Sa to the control circuit 63.
[0282] FIG. 11 is a schematic diagram showing a GOP forming the
MPEG2 bit stream. In the MPEG2 bit stream, an intra-picture data,
which can be decoded independently, without referring to other
pictures, is present at the head of each GOP. The syntax analyzer
65 therefore detects a GOP header indicating the head of each GOP,
and the counter 66 generates a timing signal. In this way, the
intra-picture data immediately succeeding the GOP header can be
extracted by the data extractor 67.
[0283] When the rotary drum is stopped in normal speed replay, the
drum rotates for several tracks after a stop control signal is
generated and until the drum is actually brought to a standstill,
and when the replay is resumed by starting rotation of the rotary
drum a certain servo pull-in time is required. The length of the
intra-picture data in the MPEG2 bit stream having been
variable-length encoded is not constant, and the period from the
detection of intra-picture data to detection of next intra-picture
data is not constant. Accordingly, in the pre-roll method, the tape
is rewound for a certain period from the end of the detected
intra-picture data, to ensure the detection of the next
intra-picture data.
[0284] Referring to FIG. 10, it is assumed that intra-picture data
#1 is detected at the track Nos. 1 to 11, forming the addresses of
the replay tracks. The data extractor 67 extracts the intra-picture
data #1, and stores the data, and sends the intra-picture data #1,
as the slow replay data, to the selector 68, while the replay mode
signal from the replay mode signal generator 62 indicates
slow-replay. Since the replay mode signal indicates slow replay,
the selector 68 outputs the intra-picture data #1 from the data
extractor 67, to the output terminal 69.
[0285] The track address of the replay track for which the
intra-picture data #1 has been detected is identified by the track
address identifying circuit 61, and at the control circuit 63, on
the basis of the signal Sa from the counter 66, the address of the
track in which the intra-picture data #1 is recorded is detected.
As a result, the control circuit 63 generates a control signal for
stopping the transport of the tape, at the address No. 11 of the
last track from which the intra-picture data #1 is read. When this
control signal is sent via the output terminal 64 to the servo
circuit, the tape transport is stopped, and the tape is rewound
from the last track No. 11 from which the intra-picture data #1 has
been read, to a track (track No. 0) one track before the track at
the head intra-picture data #1, and then normal speed replay is
again conducted. During the period t2 to t3 when the stopping and
rewinding are conducted, the data extractor 67 outputs, as the slow
replay data, the intra-picture data #1 having been read immediately
before.
[0286] The MPEG2 bit stream is variable-length encoded, so that the
length of the intra-picture data varies. That is, more than ten
tracks (ten tracks forming a standard length for one frame in a
consumer digital VTR) may be required for recording the
intra-picture data. However, in the illustrated example, it is
assumed that the intra-picture data is recorded over ten or eleven
tracks.
[0287] FIG. 12 is a diagram showing the relationship between the
tape transport speed and the interval for the reading or extraction
of the intra-picture data. In the illustrated example, the speed
"1" is the normal replay speed, and speed "0" represents the state
in which the tape is at standstill. The reading or extraction of
the intra-picture data is conducted in a period of from time t0 to
time t1.
[0288] As shown in FIG. 10, when the normal speed replay state is
resumed (t3), the replay signal read by the head from the tape is
input via the input terminal 58, and is sent to the replay signal
processing circuit 59, where replay signal processings are applied,
and the data separation circuit 60 separates the replay data into
the bit stream from the main areas and the HP data from the copy
areas, and output them. The replay data from the replay signal
processing circuit 59 is sent to the track address identifying
circuit 61, and the data indicating the track address replayed from
the replay data is identified, and the signal indicative of the
track number is supplied to the control circuit 63. The bit stream
from the main areas, which is the normal replay data from the data
separation circuit 60 is input to the syntax analyzer 65, where the
intra-picture data in the bit stream is detected, and the counter
66 generates start and termination timing signals for extracting
the intra-picture data. The data extractor 67 extracts the
intra-picture data, and the counter 66 generates a timing signal Sa
indicating that the intra-picture data has been extracted. The
timing signal Sa is input to the control circuit 63. The control
circuit 63 receives the track address number identified by the
track address identifying circuit 61, and the signal Sa indicating
that the intra-picture data has been extracted, and when the
intra-picture data #2 next to the intra-picture data #1 which was
extracted previously is extracted, the control circuit 63 detects
the address of the track in which the intra-picture data #2 is
recorded, and at the last track where the intra-picture data is
extracted, the control signal for stopping the tape transport is
generated. When this control signal is supplied via the output
terminal 64 to the servo circuit, the tape transported is
stopped.
[0289] Referring to FIG. 10, let us assume that the intra-picture
data #2 of the tracks Nos. 51 to 62 is detected, next the
intra-picture data #1. When the intra-picture data #2 is extracted,
the data extractor 67 stores the intra-picture data #2 in
substitution for the intra-picture data #1, and outputs the
intra-picture data #2 as the slow replay data, to the selector 68.
Since the replay mode signal indicates slow replay, the selector 68
outputs the data from the data extractor 67 to the output terminal
69. Responsive to the track address number from the track address
identifying circuit 61 and the timing signal Sa indicating that the
intra-picture data #2 has been detected, the control circuit 63
generates a control signal for stopping the tape transport at the
last track of the address No. 62 where the intra-picture data #2 is
read. The tape is rewound from the last track with the address No.
62 where the intra-picture data #2 is read, to the track (track No.
50) one before the first track where the intra-picture data #2
starts, and normal speed replay is again conducted. For the period
(t6 to t7) when the stopping and rewinding are conducted, the data
extractor 67 outputs the intra-picture data #2 having extracted
immediately before the stopping as the slow replay data.
[0290] Next, the normal speed replay is again conducted, and the
operation similar to that described above is repeated, and the slow
replay is thus continued.
[0291] For still replay, like the slow replay, during the normal
speed replay, intra-picture data in the bit stream from the main
areas separated from the replay data, at the data separation
circuit 60 is detected at the syntax analyzer 65, and a timing
signal is generated at the center 66, and the intra-picture data is
extracted and stored at the data extractor 67. When the tape is at
a standstill, the intra-picture data extracted by the data
extractor 67 immediately before is kept output as the still replay
data.
[0292] As has been described, the normal speed replay and rewinding
are alternately conducted, and the intra-picture data in the bit
stream from the main areas, extracted during normal speed replay,
is stored, and output as slow or still replay data. Reproduction of
data for slow or still replay is ensured, and slow or still replay
pictures of a good quality can be obtained.
EMBODIMENT 3
[0293] In Embodiment 2, the pre-roll method was used, in which when
forward slow replay is performed, intra-picture data in the bit
stream from the main areas is extracted during normal speed replay,
and is stored, and used as image data during slow replay. The
pre-roll method can be similarly used in reverse slow replay. The
intra-picture data in the bit stream from the main areas is
extracted, and stored, and rearranged and output, and used as the
image data for the slow replay.
[0294] FIG. 13A and FIG. 13B are explanatory diagrams for showing
the control operation in the reverse slow replay in Embodiment 3.
FIG. 13A shows an example of tracks in which track address and
intra-picture data are recorded on the tracks. It is assumed that
the value of the track address (track number) increases rightward,
starting from the track address No. 0. As in Embodiment 2, the
reverse slow replay is performed by the pre-roll method, in which
normal speed replay and rewinding are conducted alternately. It is
assumed that the reverse slow replay is started from the track No.
290 in FIG. 13A.
[0295] First, normal speed replay is conducted starting at the
track No. 290, and intra-picture data #4 recorded in the track Nos.
291 to 300 in the bit stream from the main areas is detected, and
separated at the data separation circuit 60 in FIG. 9, and a timing
signal is generated by the counter 66, and the intra-picture data
#4 is extracted and stored at the data extractor 67 (t0 to t1). The
data extractor 67 outputs the intra-picture data #4 as the reverse
slow replay data, to the selector 68. Because the replay mode
signal indicates reverse slow replay, the selector 68 outputs the
data from the data extractor 67 to the output terminal 69. The
counter 66 generates a timing signal Sa indicating that the
intra-picture data #4 has been extracted, and supplies it to the
control circuit 63. The addresses of the tracks from which the
intra-picture data #4 has been detected are identified by the track
address identifying circuit 61, and the addresses of the tracks
where the intra-picture data #4 is recorded are detected at the
control circuit 63, in accordance with the signal Sa from the
counter 66. As a result, the control circuit 63 rewinds the tape
from the last track of address No. 300 from which the intra-picture
data has been detected, to a track No. 140 preceding by the number
of tracks (160 tracks in this example) within which at least one
other intra-picture data is recorded, and stops the tape (t1 to
t2), and again conducts the normal speed replay.
[0296] When the state of normal speed replay is resumed, as in the
above description, the bit stream from the main areas, forming the
normal replay data, output from the data separation circuit 60 is
input to the syntax analyzer 65. The syntax analyzer 65 detects the
intra-picture data #3 recorded in the track Nos. 151 to 160, from
the bit stream, and the counter 66 generates starting and
terminating timing signals for extracting the intra-picture data.
The data extractor 67 extracts the intra-picture data #3, and the
counter 66 generates a timing signal Sa indicating that the
intra-picture data has been extracted, and supplies it to the
control circuit 63. The control circuit 63 receives the track
address number identified by the track address identifying circuit
61, and the signal Sa from the counter 66 indicating that the
intra-picture data has been extracted, and when the intra-picture
data #3 is extracted, the control circuit 63 detects the address of
the track where the intra-picture data #3 is recorded, and stores
the number of the last track from which the intra-picture data #3
is extracted, and generates a control signal to stop the tape at
the last track No. 300 from which the previous intra-picture data
#4 was extracted (t2 to t3). This control signal is supplied via
the output terminal 64 to the servo circuit, so that the tape is
stopped.
[0297] When the intra-picture data #3 is extracted, the data
extractor 67 substitutes the intra-picture data #3 for the
intra-picture data #4, and outputs the intra-picture data #3 as the
reverse replay data, to the selector 68. Since the replay mode
signal indicates the reverse slow replay, the selector 68 outputs
the data from the data extractor 67 to the output terminal 69.
Then, the tape is rewound to a track No. 0, which is 160 tracks
preceding, by 160 tracks within which at least one other
intra-picture data is recorded, the last track No. 160 from which
the intra-picture data #3 was extracted, and is stopped (t3 to t4),
and then normal speed replay is again conducted.
[0298] When the state of normal speed replay is resumed, as in the
above description, the bit stream from the main areas output from
the data separation circuit 60 is input to the syntax analyzer 65.
The syntax analyzer 65 detects the intra-picture data #1 recorded
in the track Nos. 1 to 11, from the bit stream, and the counter 66
generates starting and terminating timing signals for extracting
the intra-picture data. The data extractor 67 extracts the
intra-picture data #1, and the counter 66 generates a timing signal
Sa indicating that the intra-picture data has been extracted, and
supplies it to the control circuit 63. The control circuit 63
receives the track address number identified by the track address
identifying circuit 61, and the signal Sa from the counter 66
indicating that the intra-picture data #1 has been extracted, and
when the intra-picture data #1 is extracted, the control circuit 63
detects the address of the track where the intra-picture data #1 is
recorded, and stores the number of the last track from which the
intra-picture data #1 is extracted.
[0299] The normal speed replay is continued, and the intra-picture
data #2 in the bit stream recorded in the track Nos. 51 to 62 is
detected, and the counter 66 generates a timing signal, and the
data extractor 67 extracts and stores the intra-picture data #2,
and a control signal for stopping the tape transport is generated
at the last track No. 160 of the intra-picture data #3 of the
previous normal speed replay (t4 to t5). This control signal is
sent via the output terminal 64 to the servo circuit, so that the
tape transport is stopped.
[0300] When the intra-picture data #1 and #2 is extracted, the data
extractor 67 rearranges the data by reversing the order, and
substitutes, for the intra-picture data #3, the intra-picture data
#2 and then the intra-picture data #1, and successively outputs
them as the slow reverse data, to the selector 68. Since the replay
mode signal indicates the reverse slow replay, the selector 68
outputs the data from the data extractor 67 to the output terminal
69.
[0301] Then, the normal speed replay is conducted, and the
operation similar to that described above is repeated. The reverse
slow replay is continued in this way.
[0302] In this way, normal speed replay and rewinding are
alternately conducted, and the intra-picture data in the bit stream
from the main areas extracted during normal speed replay is stored,
and while tape is rewound to a track preceding the track from which
the normal speed replay was started, the intra-picture data is
rearranged and output, and used as the image data for the reverse
slow replay. Thus, the data for the reverse slow replay is ensured,
and a replay picture of a good quality is obtained, and effects
similar to those of Embodiment 2 are obtained.
EMBODIMENT 4
[0303] FIG. 14 is a block diagram showing a replay system of a
digital VTR of Embodiment 4 of the invention. In the drawing,
reference numerals 58 to 60, 62, and 64 to 69 are identical to
those in the device of Embodiment 2. Reference numeral 70 a control
circuit for generating signals for controlling tape transport, and
the like during slow and still replays, and the control signals are
supplied to a servo circuit.
[0304] Intermittent drive for intermittently conducting normal
speed replay and stopping to achieve slow replay will next be
described. The operations for the normal replay and the fast replay
are identical to those in Embodiment 2, and their description is
omitted.
[0305] FIG. 15 is an explanatory diagram showing the control
operation during slow replay. The replay signal read by the head
from the tape at the normal replay speed, during the slow replay,
is input via the input terminal 58, and sent to the replay signal
processing circuit 59, where replay signal processings, such as
waveform equalization, signal detection and modulation, are
applied, and output as the bit stream of the original ATV signal
and the HP data. The data separation circuit 60 separates the
replay data into the bit stream from the main areas and the HP data
from the copy areas, and outputs the bit stream from the main areas
as the normal replay data, and collects and outputs the HP data
from the copy areas as the fast replay data. The bit stream from
the main areas forming the normal replay data, output from the data
separation circuit 60 is input to the syntax analyzer 65, where the
intra-picture data in the bit stream is detected, and the counter
66 generates a timing signal, and the data extractor 67 extracts
the intra-picture data #1 (t0 to t1). The counter 66 generates a
timing signal Sa indicating that the intra-picture data has been
detected, and supplies it to the control circuit 70.
[0306] As was described in connection with Embodiment 2, the MPEG2
bit stream is formed of a GOP (group of pictures) shown in FIG. 11,
and the intra-picture data which can be decoded independently
without referring to other pictures is present at the head of the
GOP. Accordingly, the syntax analyzer 65 detects the GOP header
indicating the beginning of the GOP, and the counter 66 generates a
timing signal, and the intra-picture data immediately after the GOP
header is extracted at the data extractor 67.
[0307] Referring to FIG. 15, let us assume that the intra-picture
data #1 is extracted at the track Nos. 1 to 11. The data extractor
67 extracts and stores the intra-picture data #1, and sends the
data as the slow replay data to the selector 68 while the replay
mode signal from the replay mode signal generator 62 indicates slow
replay. Since the replay mode signal indicates slow replay, the
selector 68 outputs the data from the data extractor 67 to the
output terminal 69.
[0308] When the extraction of the intra-picture data #1 is
completed, the counter 66 supplies the control signal 70 with a
signal Sa indicating that the intra-picture data #1 has been
extracted. The control signal 70 then generates a signal for
stopping the tape transport, so that the tape transport is stopped.
The tape is halted for a period (t2 to t3) corresponding to the
speed of the slow replay, and then normal speed replay is conducted
again. While the tape is halted, the data extractor 67 outputs the
intra-picture data #1 extracted immediately before, as the slow
replay data.
[0309] FIG. 16 shows the relationship between the tape transport
speed and the period of extraction of the intra-picture data in
Embodiment 4. The transport speed "1" represents the normal replay
speed, and transport speed "0" represents the state in which the
speed "zero", i.e., the state in which the tape is halted. The
extraction of the intra-picture data is conducted for a period from
time t4 to t5 in the drawing. That is, the extraction of the
intra-picture data after time t2 when the tape transport is stopped
is conducted for a period of from time t4 to time t5. At time t3,
when the normal speed replay state is resumed, the replay signal
read by the head from the tape is input via the input terminal 58,
and sent to the replay signal processing circuit 59, where replay
signal processings are applied. The data separation circuit 60
separates the replay data into the bit stream from the main areas
and the HP data from the copy areas, and outputs them. The bit
stream from the main areas, forming the normal replay data, output
from the data separation circuit 60, is input to the syntax
analyzer 65, which detects the intra-picture data in the bit
stream. The counter 66 generates timing signals for extracting the
intra-picture data. The data extractor 67 extracts the
intra-picture data, and the counter 66 generates a timing signal Sa
indicating that the intra-picture data has been extracted, and
supplies it to the control circuit 70. On the basis of the signal
Sa from the counter 66, indicating that the intra-picture data has
been detected, the control circuit 70 generates a control signal
for stopping the tape transport when the intra-picture data #2 next
to the intra-picture data #1 that is extracted previously. This
control signal is sent via the output terminal 64 to the servo
circuit, so that the tape transport is stopped.
[0310] Referring to FIG. 15, let us assume that the intra-picture
data #2 is extracted at the track Nos. 51 to 62, after the
intra-picture data #1. When the intra-picture data #2 is extracted,
the data extractor 67 replaces the intra-picture data #1 with
intra-picture data #2, and outputs the intra-picture data #2 as the
slow replay data, and sends the intra-picture data #2 to the
selector 68. Since the replay mode signal indicates slow replay,
the selector 68 outputs data from the data extractor 67 to the
output terminal 69. The tape is halted for a period corresponding
to the speed of the slow replay, and then normal speed replay is
again conducted. During the period (t2 to t3) when the tape is
halted, the data extractor 67 outputs the intra-picture data #2 as
the slow replay data.
[0311] Then, normal speed replay is again conducted, and the
operation similar to that described is repeated. The slow replay is
thus continued.
[0312] In still replay, as in the slow replay, intra-picture data
in the bit stream from the main areas, separated from the replay
data, at the data separation circuit 60 is detected by the syntax
analyzer 65, and the counter 66 generates a timing signal, and the
data extractor 67 extracts and stores the intra-picture data. When
the tape transport is halted, the data extractor 67 keeps
outputting the intra-picture data extracted immediate before, as
the still replay data. In this way, the normal speed replay and the
halting are intermittently conducted, to store and output the
intra-picture in the bit stream from the main areas, and use it as
the image data for slow or still replay, and the data for slow and
still replays is ensured, and slow or still replay images of a good
quality are obtained.
EMBODIMENT 5
[0313] Embodiment 5 is for providing a digital VTR which is less
easily affected by data errors due to recording and replay, and
with which fast replay at an arbitrary speed.
[0314] FIG. 17 is a block diagram showing a recording system of a
digital VTR of Embodiment 5 of the invention. In the drawing,
reference numeral 1 denotes an input terminal for a bit stream with
a packet length of 188 bytes, 102 denotes a data identifying
circuit, 103 denotes a data extracting circuit, 104 denotes a
variable-length decoder for compressed data, 105 denotes a
coefficient counter counting the number of coefficients created as
a result of the decoding, 106 denotes a data amount control
circuit, 107 denotes an EOB (end of block) appending circuit, 108
denotes a buffer, 109 denotes an address control circuit, 110
denotes a track format circuit, 111 denotes a header appending
circuit, 112 denotes a recording signal processing circuit, and 113
denotes an output terminal for a recording signal for a magnetic
tape.
[0315] When recording onto a magnetic tape is conducted,
transparent recording is conducted, and at the same time, fast
replay data is extracted and recorded. The data identifying circuit
102 decodes the header information of the bit stream input via the
input terminal 1, and selects the transport packet containing the
image of the intra-picture data. The data extraction circuit 103
extracts intra-picture data within the transport packet, from the
bit stream, and outputs the the encoded data of the image block to
the variable-length decoder 104. The variable-length decoder 104
having received the encoded code, outputs the orthogonal transform
coefficients of the image block, to the coefficient counter 105.
The coefficient counter 105 outputs the count value of the number
of the orthogonal transform coefficients to the data amount control
circuit 106. The data amount control circuit 106 receives the
coefficient count value and the amount of decoded data, and
controls the data extraction circuit 103 so that the extracted data
is accommodated in one sync block under the condition that the sum
of the count values of the orthogonal transform coefficients is
within a predetermined range.
[0316] The buffer 108 temporarily stores the bit stream and the
fast replay data output from the EOB appending circuit 107. In
doing so, it reads the data in the order in which it is recorded on
the tape, under the control by the address control circuit 109. The
data output from the buffer 108 is input to the track format
circuit 110, where sync data, ID data, parities are added for each
sync block, and the header output from the header appending circuit
111 is appended to the data input from the buffer 108, and the data
is then output to the recording signal processing circuit 112, and
then to the output terminal 113, as the recording signal to be
recorded on the tape.
[0317] FIG. 18A and FIG. 18B are diagrams for explaining the
decoding of the image block in the recording system. FIG. 18A shows
the configuration of the encoded data and the decoded data of the
image block. In the drawing, reference numeral 115 denotes an i-th
image block data, and its length is LBi (bits). Reference numeral
116 denotes orthogonal coefficients obtained by decoding the
encoded data (1, 2, . . . ) of the image block data 115. FIG. 18B
shows the configuration of the HP data for fast replay. In the
drawing, reference numeral 117 denotes data extracted from the
image block data 115, and its length is Xi (bits).
[0318] FIG. 19 is a flow chart showing the procedure of decoding
the image block in the recording system. The method for determining
the amount of extracted data at the data amount control circuit 106
will next be described with reference to FIG. 18A, FIG. 18B and
FIG. 19. The reference marks used in FIG. 18A, FIG. 18B and FIG. 19
in connection with the image block data are as follows:
[0319] i: image block number
[0320] LBi: data length (number of bits) of the i-th image block
data 115
[0321] Xi: data length (number of bits) of the HP data extracted
from the i-th image block
[0322] j: number of the encoded code forming an image block
[0323] Lj: length (number of bits) of the j-th encoded code
[0324] Cj: number of orthogonal transform coefficients obtained by
decoding the j-th encoded code
[0325] L.sub.EOB: length (number of bits) of the EOB code
[0326] TM: control target of data amount (number of bits) for
recording in the sync block
[0327] D: permissible maximum value (number of bits) of vacant
capacity
[0328] d: vacant capacity (number of bits)
[0329] S: sum of the numbers Cj of the j-th orthogonal transform
coefficient
[0330] CL: contact not smaller than 2
[0331] CH: constant larger than CL
[0332] Referring to FIG. 19, when the fast replay data is newly
extracted, the control data is initialized so that the number i of
the image block is set to 1, and the vacant capacity d is set to TM
(step a1--hereinafter simply referred to as a1), and the data 115
of the i-th image block is read (a2). The length of the entire
image block data 115 is LBi bits, and the length of the encoded
code j which is a constituent thereof is Lj bits, and an EOB code
of a length of L.sub.EOB is present at the end of the encoded
code.
[0333] In the image block data 115, the encoded codes for the
low-frequency coefficients appear first. The value j is initialized
to "1" (a3) and then the encoded codes are decoded by the
variable-length decoder 104 (a4) to obtain Cj orthogonal transform
coefficients (a5). The number Cj of the orthogonal transform
coefficients varies with the encoded code j. The values Cj obtained
by counting by the coefficient counter 105 are accumulated, and the
resultant sum S of the numbers Cj of the orthogonal transform
coefficients, up to the j-th encoded code is determined (a6). The
accumulated value S is compared with a predetermined value CL (a7).
If S is greater than CL, it is then compared with another constant
CH greater than CL (a8).
[0334] When the accumulated value S is smaller than CL, judgement
is made whether the length of the code including the encoded codes
having been decoded, with the EOB appended, is not longer than the
vacant capacity d (a9). If it is not longer, j is incremented by
one (a13), and the operation returns to the step a4. When the
accumulated value S is not smaller than CL and not larger than CH,
judgement is made whether the length of the code including the
encoded codes having been decoded, with the EOB appended, is not
longer than the vacant capacity d (a10). If it is not longer, the
VLC codes (variable length codes) up to the j-th code are extracted
(a11). If the accumulated value S is judged to be larger than CH at
the step a8, and or if the code length is judged to exceed the
vacant capacity d, the VLC codes up to the (j-1)-th code are
extracted (a12).
[0335] An EOB code is appended at the EOB appending circuit 107, to
the codes 117 that have thus been extracted (a14), and the sum Xi
of the length of the j or (j-1) data having been extracted and the
EOB code is determined (a15).
[0336] The sum (.SIGMA.Xi) of the length Xi of the data having been
extracted is subtracted from the data amount target TM to find the
vacant capacity d (a16), and judgement is made whether d is not
larger than a permissible value D (a17). If the vacant capacity d
is larger than the permissible value D, i is incremented by one
(a19), and the operation returns to the step a2, and the next image
block is read. If d is not larger than the permissible value D at
the step a17, the data up to the image block i is output as the
fast replay data to the buffer 108 (a18).
[0337] FIG. 20 shows the recording pattern of the fast replay data.
In the drawing, reference numeral 141 denotes the data region of 77
byte long, 156 denotes a header of one byte appended at the header
appending circuit 111, and i and (i+1) denote data of the image
blocks for high speed replay read from the buffer 108. Recorded in
the header 156 is identification information for intra-frame and
the image blocks obtained by extracting the fast replay data. The
data of each image block is recorded, without being divided into a
plurality of sync blocks. The constant TM is dependent on the
length of which can be data recorded in the sync block, and CL and
CM define the upper and lower limits for the number of the
transform coefficients of the image used for the fast replay. By
the above procedure, the encoded data corresponding to the
orthogonal transform coefficients of the length which is not
smaller than CL and not larger than CM is extracted from the bit
stream, and used as the fast replay data. The fast replay data is
recorded in the data regions of one sync block on the magnetic
tape, without the data of the image block being divided, with the
vacant capacity being not larger than D.
[0338] In the transparent recording, two packets of 188 byte long
in the bit stream are recorded in five sync blocks on the tape.
Each packet is read by the buffer 108, and then read by the address
control circuit 109, and divided into three, by selection of a bit,
and according to the predetermined bit position. The data of two
packets, having been divided, is input to the track format circuit
110, and a header generated by the header appending circuit 111 is
appended, and the recording data of five consecutive sync blocks is
reconstructed.
[0339] FIG. 21 shows a recording pattern of the packet. It
illustrates, in two-dimensional representation, the data of five
sync blocks consecutive on the tape region in which transparent
recording is made. In the drawing, reference numeral 141 denotes a
data region of 77 bytes in one sync block, and the five rows
respectively represent data of five sync blocks. Reference numerals
142 to 144 denote data of the first packet read from the buffer
108. Reference numerals 145 to 147 denote data of the second packet
read from the buffer 108. Reference numerals 148 to 152 denote
first headers, each one byte long, appended at the header appending
circuit 111. Reference numerals 153 and 154 denote second headers,
each two bytes long, appended at the header appending circuit
111.
[0340] Regions 142 to 144 are respectively 74 bytes, 76 bytes and
38 bytes long, and the first packet is expressed by 188 bytes in
total. Regions 145 to 147 are respectively 36 bytes, 76 bytes and
76 bytes long, and the second packet is expressed by 188 bytes in
total.
[0341] The regions 148 to 152 are headers, and contain a flag
indicating whether the corresponding sync block is a region for
transparent recording or a recording region for fast replay data, a
flag for identifying which of the five consecutive sync blocks, and
a code for indicating the partition for of the first encoded data
of the succeeding packet data.
[0342] The regions 153 and 154 contain codes for indicating the
type of the data of the packet, e.g., video data, audio data,
character data and program data.
[0343] FIG. 22 shows the recording track on the magnetic tape. In
the drawing, reference numeral 160 denotes a track, 158 denotes a
video recording region, 161 denotes a transparent recording region,
and 162 denotes fast replay data recording region. The numerical
values along the track represent the sync block numbers for the
video regions. The region 161 consists of five sync blocks
consecutive to each other, and records the bit stream data shown in
FIG. 21. The region 162 is one sync block adjacent to the region
162, and records the fast replay data in the format shown in FIG.
20. The regions 161 and 162 are disposed alternately in the video
recording region 158.
[0344] FIG. 23 is a block diagram showing a replay system of a
digital VTR of Embodiment 5. In the drawing, reference numeral 121
denotes a replay signal input terminal, 122 is a data separation
circuit for separating the transparent recording data and fast
replay data from each other, 123 denotes a buffer for forming a bit
stream, 124 denotes a synthesizing circuit for fast replay data,
125 denotes a bit stream forming circuit for fast replay data, 126
denotes a fast replay speed selecting circuit, and 127 is an output
terminal for the bit stream.
[0345] The signal replayed from the magnetic tape is input via the
input terminal 121 to the data separation circuit 122, and is
separated into the transparent recording data and the fast replay
data. The transparent recording data is read at a predetermined
rate, in a sequence by the buffer 123, and the data of a plurality
of packets which were recorded, being divided, are read in sequence
at a predetermined rate, so that a bit stream identical to those is
output via the output terminal 127.
[0346] When fast replay is to be conducted, the speed selection
circuit 126 controls the entire system so that the tape transport
speed is at an even-multiple speed, and the fast replay data
synthesizing circuit 124 collects the fast replay data without
duplication, on the basis of the signals replayed by the head. When
the fast replay data is replayed, the data of the intra frame is
constructed and output to the bit stream forming circuit 125. The
bit stream forming circuit 125 repeats the intra-frame data for a
predetermined number of times, on the basis of the speed data from
the speed selection circuit 126, and adds a packet header to it, to
form bit stream data. The bit stream data that has been formed is
output to the buffer 123, and is output from the buffer 123 at a
predetermined rate.
[0347] Factors affecting the scanning pattern of the head at the
time of the fast replay include the number and disposition of the
heads on the drum, the width of each head, the angle over which the
tape is wrapped around the drum, and the tape transport speed. Head
scanning patterns on the assumption that two head of different
azimuths are disposed on the drum 180.degree. apart, and the angle
over which the tape is wrapped around the drum is 180.degree. will
next be shown.
[0348] FIG. 24 shows the track format and head scanning pattern
when the tape is double-speed replayed. In the drawing, the
character ("A" or "B") written in each track 160 indicates whether
the head used for recording the track is head A or head B.
Reference numeral 171 denotes the scanning regions by a first head
A, and reference numeral 172 denotes the scanning region by a
second head B. Reference numeral 173 denotes tape region where data
can be replayed by the first head A, and reference numeral 174
denotes tape region where data can be replayed by the second head
B. The width of the head is assumed to be identical to the width of
the track, and the tracks which are actually inclined are shown to
be perpendicular to the longitudinal direction of the tape, for the
sake of simplicity of illustration.
[0349] The data recorded in the regions 173 and 174 can be picked
up, but as the overlapping between the track and the head becomes
small, the signal level become insufficient, so that the data
cannot be reproduced. Usually, when the head and track overlaps
more than half the track width, then the data can be replayed.
Accordingly, data can be replayed from the part of the region 173
below the line 175 and the part of the region 174 above the line
175.
[0350] In the double-speed replay, if fast replay data is
repeatedly recorded over four consecutive tracks as indicated by
176, all the data can be replayed if scanned twice by the heads A
and B. However, identical data need to be recorded in identical
sync blocks of the four tracks.
[0351] The number of times the fast replay data is repeatedly
recorded can be determined from the specification for the fast
replay speeds of the device, and is set to be twice the multiplier
of the maximum fast replay speed.
[0352] FIG. 25 shows the track pattern and the head scanning
pattern when the recorded tape is four-time speed replayed. In the
drawing, the reference numerals identical to those in FIG. 24
denote identical elements. Lines 181 and 183 show the head scanning
regions if the head width is 1.5 times the track width. As
described above, for four-time speed replay, fast replay data must
be repeatedly recorded at least (4.times.2) or 8 times, to enable
replay of all the data. However, in actual fast replay, the tape is
transported at a high speed, so that the contact between the head
and the tape is unstable, and the level of the replay signal may
fluctuate. Moreover, as the tape transport speed varies a little,
the head scanning pattern may shifts from that illustrated. The
regions 173 and 174 may not cover all the data. In such a case, by
using a head of a width W2 (=W1.times.1.5, W1 representing the
width the track), data in the regions 183 and 184 can also
replayed, and all the fast replay data can be replayed. This is
next explained further.
[0353] FIG. 26A shows the signal level when the head of a width W1
is used for replay from a track pattern shown in FIG. 25, and the
track regions from which data replay is possible. In the drawing,
the horizontal axis represents the position in the longitudinal
direction of the track, and the vertical axis represents the replay
signal level. 191 represents the replay signal level by the head A,
192 represents the replay signal level by the head B, 193
represents the half peak value, 194 denotes the recording region
from which the fast replay data repeatedly recorded can be replayed
by the head A, and 195 denotes the recording regions from which the
data can be replayed by the head B.
[0354] By adding the regions 194 and 195, all the fast replay data
recorded along the entire length of the tracks can be replayed.
However, when the replay signal level varies, the data in the
peripheries of the regions 194 and 195 may not be replayed, and
when the tape transport speed fluctuates, the regions 194 and 196
may shift left or right, for example. In these cases, all the fast
replay data cannot be replayed from the addition of the regions 194
and 195.
[0355] FIG. 26B shows the signal level when the head of a width W2
is used for replay from the track pattern shown in FIG. 25, and the
track regions from which data replay is possible. When compared
with FIG. 26A, the signal levels 191 and 192 are increased by the
amount corresponding to the regions 183 and 184. As a result, the
fast replay data of all the track are replayed sufficiently from
the addition of the regions 194 and 195 from which replay is
possible.
[0356] In Embodiment 5, description is made for the case where the
track format is as shown in FIG. 22. However, the fast replay data
may be concentrated in a specific part of a track, for instance in
the central part of the track. In this case, the parts of the track
near the tape edges where the signal level fluctuation is larger
are not used, so that the fast replay data can be replayed
stably.
[0357] The fast replay data may be concentrated at the beginning
ends. In this case, it is possible to reduce the angle over which
the tape is wrapped around the drum, to thereby reduce the load on
the tape transport system. In this way, the tape transport can be
thereby stabilized, and the speed for the fast replay can be
increased.
[0358] In Embodiment 5, the fast replay data is repeatedly recorded
for a number twice the multiplier of the maximum fast replay speed.
By adding a head C for use in fast replay only, having the same
azimuth as the head B, and being disposed near the head A, the fast
replay data recorded by the head B can be replayed simultaneously
with the scanning by the head A. In this case, the speed of the
fast replay can be increased to double the multiplier of the
above-mentioned maximum fast replay speed.
[0359] In Embodiment 5, the fast replay data is recorded each sync
block by sync block, but may alternatively be recorded, taking
every two sync blocks as a unit. In this case, the constant TM is
set to 76 bytes.times.2.times.8=1216 bits.
EMBODIMENT 6
[0360] FIG. 27 is a block diagram showing a recording system of a
digital VTR of Embodiment 6 of the invention. In the drawings,
reference numeral 1 denotes an input terminal for receiving the
digital video signal in the form of a bit stream, 202 denotes a
packet detecting circuit for detecting packets of the video signal
from the bit stream having been supplied, 203 denotes a first
memory for storing the data from the packet detecting circuit 202,
packet by packet, 204 denotes an intra detecting circuit for
detecting whether the transport packet contains an intra-picture
data, 205 denotes a fast replay data generating circuit receiving
the transport packet containing intra-picture data and forming fast
replay data, and 206 denotes a second memory for storing the fast
replay data formed by the fast replay data generating circuit 205.
Reference numeral 207 denotes a first first header appending
circuit for appending a header to the data read from the first
memory 203. Reference numeral 208 denotes a second header appending
circuit for appending a header to the data read from the second
memory 206. Reference numeral 209 denotes a format circuit for
forming video areas from the input data, 210 denotes a error
correction encoder for performing error correction encoding, 211
denotes digital modulator for conversion into data suitable for
recording on the tape, 212 denotes a recording amplifier, 213
denotes a rotary drum, and 214a and 214b denote magnetic heads.
[0361] FIG. 28 shows data format of the video areas in the digital
VTR.
[0362] FIG. 29 to FIG. 31 show data packets according to this
embodiment. FIG. 29 shows the configuration of the transport data
packet contained in the input bit stream. FIG. 30 shows the
configuration of data of the main area recorded on the magnetic
tape. FIG. 31 shows the configuration of data in the copy area.
[0363] The operation in the recording in the digital VTR of
Embodiment 6 will next-be described with reference to FIG. 27 to
FIG. 31. The bit stream input via the input terminal 1 contains
digital video and audio signals, and digital data signals
concerning the video and audio signals, and they are transmitted,
being partitioned into transport packets, as shown in FIG. 29. Each
transport packet comprises a header of 4 bytes, and a data section
of 184 bytes.
[0364] In the present digital VTR, low-frequency components are
extracted from the transport packets containing intra-picture data
to form fast replay data, or so-called HP data, and the transport
packets are recorded in the main areas and the fast replay data is
recorded in the copy areas. The input bit stream is supplied to the
packet detecting circuit 202 where the transport packets are
detected, and sent to the first memory 203 and the intra detecting
circuit 204.
[0365] The first memory 203 stores the bit stream data packet by
packet, and the data is read so that it forms recording data packet
shown in FIG. 30. FIG. 30 shows the case where the length of data
within one sync block is 77 bytes, and two transport packets are
used to form five sync blocks. In the drawing, H1 denotes a first
header, and H2 denotes a second header. H1 is positioned at the
head of each sync block, and contains a flag indicating whether the
sync block belongs to the main areas or to the copy areas. H2 is
positioned at the head of each transport packet, and contains a
flag indicating the transport packet succeeding the H2 header
contains an intra-picture data.
[0366] The transport packet data read from the first memory 203 is
input to the first header appending circuit 207, where H1 and H2
headers are appended, and made into a packet configuration shown in
FIG. 30, and is then supplied to the format circuit 209.
[0367] The intra detecting circuit 204 finds whether the data in
the transport packet contains data of intra-picture data. The fast
replay data generating circuit 205 extracts low-frequency component
from the packet containing the detected intra-picture data, to
generate HP data, and supplies it to the second memory 206.
[0368] The second memory 206 stores HP data sent from the fast
replay data generating circuit 205, and the data is read so that
the recording data configuration is as shown in FIG. 31. In the
drawing, H1 denotes a first header identical to that in FIG. 30.
The fast replay data read from the second memory is supplied to the
second header appending circuit 208, where H1 header is appended,
and is formed into the configuration shown in FIG. 31, and sent to
the format circuit 209.
[0369] The format circuit 209 combines the data from the main areas
output from the header appending circuit 207, and the data from the
copy areas output from the second header appending circuit 208 to
form data of one track, and sends it to the error correction
encoder 210, where error correction encoding is performed on input
data of one track. The output of the error correction encoder 210
is digital-modulated at the digital modulator 211 into data format
suitable for recording on the tape, and passed through the
recording amplifier 212, and recorded on the magnetic tape by means
of the rotary heads 214a and 214b.
[0370] The operation for normal replay will next be described.
[0371] FIG. 32 is a block diagram showing a replay system of a
digital VTR of Embodiment 6. In the drawing, reference numerals
213, 214a and 214b denote members identical to those in FIG. 27.
Reference numeral 215 denotes a replay amplifier, 216 denotes a
digital demodulator, 217 denotes a sync header detecting circuit,
218 denotes a third memory, 219 denotes an error correction decoder
for correction replay errors, 220 denotes a data separation circuit
for separating the data by checking H1 header in each sync block,
and selectively outputting data according to the replay mode, 221
denotes an intra detection circuit for checking H2 header in the
data output from the data separation circuit 220, and finding
transport packets containing an intra-picture data, 222 denotes a
data extractor for extracting transport packets containing an
intra-picture data, and 223 denotes a fourth memory for extracting
for storing the data extracted by the data extractor 222. Reference
numeral 224 denotes a selector for selectively outputting the data
according to the replay mode, and 225 denotes an output terminal
for outputting the data selected by the selector 224.
[0372] In normal replay, the data replayed by the magnetic heads
214a and 214b from the magnetic tape is amplified by the replay
amplifier 215, and is input to the digital demodulator 216. The
digital demodulator 216 performs digital demodulation on the input
data, and outputs the demodulated data to the sync header check
circuit 217. The sync header check circuit 217 checks sync headers
in the demodulated sync blocks, and stores the data in the third
memory 218, according to the header information that has been read.
Any replay errors in the data recorded in the third memory 218 are
corrected, and the error-corrected data is output to the data
separation circuit 220.
[0373] The data separation circuit 220 checks the H1 headers in the
data read from the third memory 218, and separates it into normal
replay transport packets, and fast replay data, and outputs the
normal replay transport packets to the selector 224, and outputs
the H2 headers having been appended to the head of the transport
packet to the intra detection circuit 221. At this stage, the H1
and H2 headers are removed from the transport packets.
[0374] The intra detection circuit 221 reads the H2 header output
from the data separation circuit 222, and checks whether the
transport packet to which the H2 header has been appended contains
an intra-picture data. If an intra-picture data is contained, the
intra detection circuit 221 sends a control signal for causing the
the data extractor 222 to extracts the packet. In accordance with
the control signal from the intra detection circuit 221, the data
extractor 222 extracts the transport packet, and outputs it to the
fourth memory 223. As a result, the transport packets extracted by
the data extractor 222 are sequentially stored in the fourth memory
223.
[0375] The selector 224 selectively outputs the output of the data
separation circuit 220, or the output of the fourth memory 223, to
the output terminal 225. In normal replay, the output from the data
separation circuit 220 is selected, and output via the output
terminal 225.
[0376] Next, let us consider a situation case where a still replay
mode is selected during normal replay. In normal replay, the data
replayed by the magnetic heads 214a and 214b from the magnetic tape
is amplified by the replay amplifier 215, and is then input to the
digital demodulator 216. The digital demodulator 216 performs
digital demodulation on the input data, and outputs the demodulated
data to the sync header check circuit 217. The sync header check
circuit 217 checks the sync header in the demodulated sync block,
and stores the data in the third memory 218 according to the header
information that has been read. Any replay errors contained in the
data recorded in the third memory 218 are corrected at the error
correction decoder 219. and the error-corrected data is output to
the data separation circuit 220.
[0377] The data separation circuit 220 checks the H1 headers in the
data read from the third memory 218, and separates it into normal
replay transport packets, and fast replay data, and outputs the
normal replay transport packets to the selector 224, and outputs
the H2 headers having been appended to the head of the transport
packet to the intra detection circuit 221.
[0378] The intra detection circuit 221 reads the H2 header output
from the data separation circuit 222, and checks whether the
transport packet to which the H2 header has been appended contains
an intra-picture data. If an intra-picture data is contained, the
intra detection circuit 221 sends a control signal for causing the
the data extractor 222 to extracts the packet. In accordance with
the control signal from the intra detection circuit 221, the data
extractor 222 extracts the transport packet, and outputs it to the
fourth memory 223. As a result, the transport packets extracted by
the data extractor 222 are sequentially stored in the fourth memory
223.
[0379] The selector 224 selectively outputs the output of the data
separation circuit 220, or the output of the fourth memory 223, to
the output terminal 225. In normal replay, the output from the data
separation circuit 220 is selected, and output via the output
terminal 225.
[0380] When still replay is selected during normal replay, the
output of the transport packets for normal replay is stopped, and
the output of the data from the selector to the output terminal 225
is terminated. The input to the selector 224 is switched, and the
output of the fourth memory 223 is selected, so that still picture
can be output via the output terminal 225.
[0381] Slow replay will next be described. During slow replay, the
magnetic tape transport speed is lower than in normal replay, and
the magnetic tape is transported while the same helical track is
scanned and replayed a plurality of times. In particular, when the
tape speed is 1/2 multiple-speed or less, the same track is
replayed at least twice, so that it is possible to replay all the
data of one track through the checking of the sync header at the
sync header check circuit 217, and the error correction at the
error correction decoder 219. The replayed data is recorded in the
third memory 218.
[0382] The data separation circuit 220 checks the H1 headers in the
data read from the third memory 218, and separates it into normal
replay transport packets, and fast replay data, and outputs the
normal replay transport packets to the selector 224, and outputs
the H2 headers having been appended to the head of the transport
packet to the intra detection circuit 221.
[0383] The intra detection circuit 221 reads the H2 header output
from the data separation circuit 222, and checks whether the
transport packet to which the H2 header has been appended contains
an intra-picture data. If an intra-picture data is contained, the
intra detection circuit 221 sends a control signal for causing the
the data extractor 222 to extracts the packet. In accordance with
the control signal from the intra detection circuit 221, the data
extractor 222 extracts the transport packet for normal replay, and
outputs it to the fourth memory 223. As a result, the transport
packets extracted by the data extractor 222 are sequentially stored
in the fourth memory 223. The selector 224 selectively outputs the
output of the data separation circuit 220, or the output of the
fourth memory 223, to the output terminal 225. In slow replay, the
output from the data separation circuit 220 is selected, and output
via the output terminal 225.
[0384] The operation in fast replay will next be described. In fast
replay, the data replayed by the magnetic heads 214a and 214b from
the magnetic tape is amplified by the replay amplifier 215, and is
then input to the digital demodulator 216. The digital demodulator
216 performs digital demodulation on the input data, and outputs
the demodulated data to the sync header check circuit 217. The sync
header check circuit 217 checks the sync header in the demodulated
sync block, and stores the data in the third memory 218 according
to the header information that has been read. Any replay errors
contained in the data recorded in the third memory 218 are
corrected at the error correction decoder 219. and the
error-corrected data is output to the data separation circuit
220.
[0385] The data separation circuit 220 checks the H1 headers in the
data read from the third memory 218, and separates it into normal
replay transport packets, and fast replay data, and outputs only
the fast replay data to the selector 224.
[0386] The selector 224 selectively outputs the output of the data
separation circuit 220, or the output of the fourth memory 223, to
the output terminal 225. In fast replay, the output from the data
separation circuit 220 is selected, and output via the output
terminal 225.
EMBODIMENT 7
[0387] FIG. 33 is a block diagram showing a recording system of a
digital VTR of Embodiment 7 of the invention. In the drawing,
reference numeral 1 denotes an input terminal for receiving an
input bit stream, 4 denotes a variable-length decoder for analyzing
the header in the input bit stream, and detecting the intra-encoded
block to perform variable-length decoding, 5 denotes a counter for
counting the number of blocks forming the variable-length decoded
intra-picture data, 6 denotes a data extraction circuit for
extracting HP data for fast replay, from the input bit stream, in
accordance with instructions from the counter, 7 denotes an EOB
appending circuit for appending EOB codes to the HP data having
been extracted, and 258 denotes an HP data output terminal.
Reference numeral 260 denotes an HP data format circuit for
formatting the HP data according to a designated pattern, 261
denotes a track counter for counting the track numbers, and 262
denotes a pattern generating circuit for determining the position
at which the HP data is to be recorded, for each track, on the
basis of the count value at the track counter 261. Reference
numeral 263 denotes a phase signal generating circuit for
generating a phase signal having a value identical throughout each
track group, according to the input from the track counter 261.
Reference numeral 264 denotes a recording data format circuit
264.
[0388] The operation will next be described. The operation from the
input terminal 1 to the EOB appending circuit 7 is identical to
that of the prior art example of FIG. 43. The HP data output from
the EOB appending circuit 7 is input to the HP data format circuit
260, where the input HP data is stored in a memory within the HP
data format circuit 260. The track counter 261 keeps counting the
number of tracks until the recording of HP data in a designated
track group is completed. Each time recording of different HP data
in the tracks is started, the count value is reset. The count value
generated from the track counter 261 is supplied to the pattern
generating circuit 262 and the phase signal generator 263. The
pattern signal from the pattern signal generator 262 is supplied to
the HP data format circuit 260 and the recording data format
circuit 264, and the phase signal from the phase signal generating
circuit 263 is supplied to the recording data format circuit
264.
[0389] FIG. 34 shows the recording pattern of the HP data recorded
in the tracks. It is assumed that "17" is the multiplier of the
maximum fast replay speed, as in the prior art example. As in the
prior art example, two heads are disposed opposite to each other,
180.degree. apart from each other, and the tape is wrapped around
the drum over 180.degree..
[0390] "A", "B" and "C" indicate, by the same alphabetic character,
identical HP data is recorded over 17 tracks. The numerals
succeeding the alphabetic characters denotes different HP data are
recorded in different track groups, each consisting of 17 tracks.
The combinations of the alphabetic characters and numerals
indicate, as in FIG. 44, that they are identical data.
[0391] More specifically, the recording patterns of the tracks
forming one track group consisting of 17 tracks include
[0392] a pattern TP1 in which HP data B is recorded in the copy
area at the center of the track, and HP data A is recorded in the
copy areas at both ends of the track,
[0393] a pattern TP2 in which HP data A is recorded in the copy
area at the center of the track, and HP data C is recorded in the
copy areas at both ends of the track,
[0394] a pattern TP3 in which HP data A is recorded in the copy
areas at the center and both ends of the track,
[0395] a pattern TP4 in which HP data C is recorded in the copy
area at the center of the track, and HP data A is recorded in the
copy areas at both ends of the track,
[0396] a pattern TP5 in which HP data B is recorded in the copy
area at the center of the track, and HP data C is recorded in the
copy areas at both ends of the track, and
[0397] a pattern TP6 in which HP data B is recorded in the copy
areas at the center and both ends of the track, and
[0398] in one track group,
[0399] a first track of pattern TP4 is disposed in the center of
the track group,
[0400] a second track of pattern TP1 is disposed at one end (at the
head, in the illustrated example) of the track group,
[0401] a third track of pattern TP6 is disposed at the opposite end
(at the tail, in the illustrated example) of the track group,
[0402] tracks of patterns TP2 and TP3 are alternately and
repeatedly disposed between the first track and the second
track,
[0403] tracks of patterns TP5 and TP6 are alternately and
repeatedly disposed between the first track and the third
track.
[0404] The count value of the track counter 261 varies from "0" to
"16" and this enables identification of each of the 17 tracks in
each track group. The count value of the track counter 261 is reset
every 17 tracks. The track counter 261 generates such a count
value, and outputs it to the pattern generating circuit 262 and the
phase signal generator 263.
[0405] FIG. 35 shows the pattern signal generated by the pattern
generating circuit. The track counter 261 is reset at the head of
17 tracks, and its count value is incremented by one every track,
and its count value is output to the pattern generating circuit
262. On the basis of the value input from the track counter 261,
the pattern generating circuit 262 outputs a pattern signal, as a
signal for specifying HP data to be recorded in the particular
track. For instance, when a pattern shown in FIG. 34 is to be
generated, at the first track in the group of tracks consisting of
17 tracks, the value of the track counter 261 is "0", and the
pattern generating circuit 262 outputs a pattern ABA (FIG. 35)
corresponding to the counter value "0". The pattern generating
circuit 262 has a arrangement map for HP data for 17 tracks shown
in FIG. 35, and specifies one of the pattern signals from the
arrangement table, depending on the value of the track counter 261
input to the pattern generating circuit 262. According to the
pattern signal generated by the pattern generating circuit 262, the
HP data format circuit 260 outputs the HP data in the order of A,
and B and again A. The pattern signal from the pattern generating
circuit 262 is also sent to the recording format circuit 264.
[0406] The track counter 261 also outputs the counter value to the
phase signal generator 263. The phase signal generator 263
generates a phase whose value varies every 17 tracks and maintained
constant for the period of 17 tracks. The value of the phase signal
varies every 17 track period, and within each track group formatted
with an identical phase signal, the 17 track and next 17 tracks or
immediately preceding 17 tracks can be discriminated. The phase
signal is also input to the recording data format circuit 264. The
phase signal generator 263 receives the input from the track
counter 261, and varies its value. As long as it is possible to
discriminate between the group of 17 tracks to which the particular
track belongs, and the group of 17 tracks which are crossed during
fast replay, any other signal may be used. If for instance, the
multiplier of the fast replay speed is 17, two groups of 17 tracks
are crossed, and it is sufficient if the two groups of the 17
tracks are discriminated from each other. The phase signal
generator 263 may therefore generates a one-bit signal of "0" and
"1", alternately.
[0407] FIG. 36 shows the data configuration of the track. FIG. 37
shows the data configuration of the sync block. The recording data
format circuit 264 forms data of a track as shown in FIG. 36. The
sync block numbers allotted to the video area are from No. 0 to No.
134. At three locations in the video area, HP data areas are
provided, and the HP data output from the HP data format circuit
260, together with the pattern signal from the pattern generating
circuit 262 and the phase signal from the phase signal generator
263, are output via the output terminal 258. As shown in FIG. 37,
the sync blocks are one of the two types, i.e., a first type of
sync blocks 265 in the main areas, in which ATV bit stream, and
parities are recorded, after SYNC and ID, and a second type of sync
blocks 266 in the copy areas, in which, after SYNC and ID, the
phase signal (PHASE) from the phase signal generator 263, the HP
data number which can be identified by the signal from the pattern
generating circuit 262, and then the HP data and parities are
recorded. These sync blocks form part of the data of the track. In
addition to these data, sync blocks in the AUX data area as defined
for the VTR of the SD specification, form the data of the track. In
this way, the data on the tape shown in FIG. 34 is formed. With the
data thus formed, the fast replay can be conducted with any of a
number of different multiple-speeds. For instance, +3-time fast
replay cannot be achieved with the arrangement of data of the prior
art example shown in FIG. 44. This is because, the HP data recorded
in the center of the tracks on the tape that is scanned, and the HP
data at both ends of the tracks are always of different
azimuths.
[0408] If however, the HP data is arranged as in Embodiment 7,
while the 17 tracks with an identical phase signal are scanned by
the head, at least one set each of A, B and C HP data can be
obtained. It is possible to detect whether the data is HP data or
not, from the sync block number contained in the ID, and when the
data is found to be HP data, then discrimination is made to find
which of the A, B and C HP data, the detected HP data with an
identical phase signal is, and while the head scans the 17 tracks,
at least one set each of the A, B and C HP data can be
obtained.
[0409] In Embodiment 7, one track groups consists of 17 tracks. But
the invention is not limited to such configuration of the track
group, and each track group may consists of tracks the number of
which is given by:
6.times.m+5, or
4.times.n+5,
[0410] where m and n are integers not smaller than "1", and
satisfying 3.times.m=2.times.n. According, it is sufficient if I
track groups (I being a positive integer) are formed of J tracks
where J=12.times.I+5.
[0411] In Embodiment 7, it is assumed that all the intra-picture
data contained in the input bit stream are used. Detection of the
intra-picture data can be facilitated if only those intra-picture
data which are contained in the intra-frame or intra-field the are
used. This is because when variable-length decoding is effected the
header of the input bit stream is detected, and the intra-picture
data is recognized from the header. When the intra-picture data
used as the HP data is limited to intra-frame or intra-field, it is
not necessary to detect the intra information attendant to the
macro block, and the picture header attendant to the head of one
frame can be utilized to simplify the detection of intra-picture
data.
EMBODIMENT 8
[0412] FIG. 38 shows a recording pattern of HP data on tracks in
Embodiment 8.
[0413] In Embodiment 7, the recording pattern shown in FIG. 34 is
used. In Embodiment 8, the recording patterns of the tracks forming
one track group include
[0414] a pattern TP1 in which HP data B is recorded in the copy
area at the center of the track, and HP data A is recorded in the
copy areas at both ends of the track,
[0415] a pattern TP2 in which HP data A is recorded in the copy
area at the center of the track, and HP data B is recorded in the
copy areas at both ends of the track,
[0416] a pattern TP3 in which HP data A is recorded in the copy
areas at the center and both ends of the track,
[0417] a pattern TP4 in which HP data A is recorded in the copy
area at the center of the track, and HP data C is recorded in the
copy areas at both ends of the track,
[0418] a pattern TP5 in which HP data C is recorded in the copy
area at the center of the track, and HP data A is recorded in the
copy areas at both ends of the track,
[0419] a pattern TP6 in which HP data C is recorded in the copy
areas at the center and both ends of the track,
[0420] a pattern TP7 in which HP data C is recorded in the copy
area at the center of the track, and HP data B is recorded in the
copy areas at both ends of the track,
[0421] a pattern TP8 in which HP data B is recorded in the copy
area at the center of the track, and HP data C is recorded in the
copy areas at both ends of the track, and
[0422] a pattern TP9 in which HP data B is recorded in the copy
areas at the center and both ends of the track, and
[0423] in one track group,
[0424] a first track of pattern TP5 is disposed in the center of
the track group,
[0425] second and third tracks of pattern TP6 are disposed on both
sides of and adjacent to the first track of pattern TP5,
[0426] a fourth track of pattern TP5 is disposed adjacent one of
the second and third tracks of pattern TP6,
[0427] a fifth track of pattern TP7 is disposed adjacent the other
of the second and third tracks, and on the opposite side of the
fourth track of pattern TP5, with respect to the first track,
[0428] a sixth track of pattern TP1 is disposed at the head or tail
(at the head in the illustrated example) of the track group, and on
the same side of the first track as the fourth track,
[0429] a seventh track of pattern TP2 is disposed next to the track
of pattern TP1, and on the same side of the first track as the
fourth track,
[0430] an eighth track of pattern TP9 is disposed at the tail or
head (at the tail, in the illustrated example) of the track group,
and on the same side of the first track as the fifth track,
[0431] tracks of patterns TP3 and TP4 are alternately and
repeatedly disposed between the seventh track and the fourth
track,
[0432] tracks of patterns TP8 and TP9 are alternately and
repeatedly disposed between the eighth track and the fifth
track.
[0433] In Embodiment 8, each track group consists of 17 tracks. The
invention is not limited to the particular number of the tracks,
and may also be applicable if the number of tracks forming a track
groups is a track number given by 6.times.m+5 or 4.times.n+5 where
m and n are integers not smaller than 1 and satisfying
3.times.m=2.times.n, that is the number of tracks forming a track
group may be J given by J=12.times.I+5, where I is a positive
integer.
[0434] In Embodiment 8, the intra-picture data contained in the
input bit stream are all used. But detection of intra-picture data
is facilitated if intra-picture data contained in intra-frame or
intra-field.
[0435] This is because of the following reason. That is, when
variable-length encoding is performed, the header of the input bit
stream is detected, and the intra-picture data is recognized from
the header. But if the intra-picture data used as the HP data is
limited to intra-frame or intra-field, it is unnecessary to detect
intra-information attendant to the macro blocks and the detection
of the intra-picture data can be simplified by utilizing the
picture header attendant to the head of one frame.
EMBODIMENT 9
[0436] In connection with Embodiment 9, replay from the tape
recorded in Embodiment 7 and Embodiment 8 is explained. FIG. 39A
and FIG. 39B show an example of replay system of a digital VTR of
Embodiment 9. It is assumed, as in the prior art example, that the
drum has two heads opposite to each other, and 180.degree. apart
from each other, and the tape is wrapped around the drum over
180.degree..
[0437] Reference numeral 270 denotes main areas in which the input
bit stream is recorded on the tape, without modification, 271
denotes copy areas in which the low-frequency components of the DCT
coefficients of the intra-picture data, extracted from the input
bit stream, are recorded as HP data, 272 denotes a data separation
circuit for selecting the output replay bit stream from the bit
stream from the main areas and the bit stream from the copy areas,
and 273 denotes a data reconstruction circuit for combining, for
reconstruction, the HP data output from the data separation circuit
during fast replay.
[0438] During normal replay, the data from the main areas 270 and
the data from the copy areas 271 are input and judgement is made
whether the sync block of the main area or the sync block of the
copy areas is being replayed, in accordance with the ID in the sync
block, and the data of the main areas is selected as the replay
data.
[0439] During fast replay, the data separation circuit 272 outputs
the sync blocks from the copy areas, in accordance with the ID's
from the respective sync blocks. The data reconstruction circuit
273 checks the phase signal of the data of the input sync block,
checks the HP data number in the sync blocks having identical phase
signal, and forms a set of three HP data recorded in one track
group. In this way, a bit stream of intra-picture data is formed,
and is output to the decoder.
[0440] FIG. 40 is a diagram showing a scanning trace of the rotary
head at the time of seven-time speed replay. The operation of the
seven-time speed replay from the magnetic tape of the recording
pattern of FIG. 34 will next be described. One track group
consists, for example of 17n tracks, as indicated by RP, at the
bottom of the drawing, and A, B and C HP data are recorded 17 times
each. Let us consider a situation where first and second heads scan
at a seven-time speed.
[0441] When the first head records tracks without hatching, and the
second head records tracks with hatching. When the first head scans
as shown on the left side of the drawing only data A1 can be
obtained as the HP data because of the azimuth. The data A1 is
stored in the data reconstruction circuit 273. When the second head
scans, only data C1 can be obtained. This data is also stored in
the data reconstruction circuit 273. The phase signal is then
checked, and if it is identical to the phase signal of A1 earlier
obtained, then the data C1 is stored together with A1. If the phase
signal is different, the data A1 is discarded, and only the data C1
is stored. In this case, the HP data of the A1 and C1 are stored.
Finally, the data B1 and C1 can be obtained when the first head
scans the tape. The phase signal of the data B1 is identical to
that of A1 and C1, but the phase signal of the data C2 is different
from that of A1 and C1. When B1 is obtained, a set of A1, B1 and C1
is completed, and the HP data is reconstructed. The C2 data is
newly stored.
[0442] In this way, the bit stream from the main areas 270 can be
replayed during normal replay, and HP data is reconstructed during
fast replay to reproduce bit stream of intra-picture data.
* * * * *