United States Patent
`[19]
`[11] Patent Number:
`6,028,726
`
`Yanagihara
`[45] Date of Patent:
`*Feb. 22, 2000
`
`US006028726A
`
`[54] DIGITAL DATA RECORDING/
`58501238533185?211531388311};
`TO A DATA PACKET
`
`[75]
`
`Inventor: Naofumi Yanagihara, Tokyo, Japan
`
`[73] Assignee: Sony Corporation, Tokyo, Japan
`.
`.
`.
`.
`.
`.
`I * l Notice:
`This patent 15 subject to a terminal dls'
`claimer.
`
`[21] Appl. N0.: 08/929,744
`,
`.
`F1169
`
`591" 15’ 1997
`
`[22]
`
`Related US. Application Data
`
`[63] Continuation of application No. 08/556,492, Nov. 13, 1995,
`abandoned.
`
`_
`_
`_
`_
`,
`[30]
`Foreign Application Priority Data
`Nov. 14, 1994
`[JP]
`Japan .................................... 6304421
`Jan 27 1995
`[JP]
`Ja an
`7—031685
`.
`’
`p
`iiiiiiiiiiiiiiiiiiiiiiiiiiiiiii
`Int. Cl.7 .............................. G11B 5/09; H04N 5/783
`[51]
`52 U811 .................................. 3w483w513%B1
`[
`l
`/
`,
`,
`[58] Field of Search ................................................. 360/48
`
`[56]
`
`References Cited
`
`U'S' PATENT DOCUMENTS
`12/1994 Lane et a1.
`................................ 386/81
`5,377,051
`8/1996 Park et a1.
`360/53
`5,546,244
`
`5,561,652 10/1996 Fujiwara et al.
`369/59
`5,845,042 12/1998 Yanagihara ............................... 386/81
`
`5,845,043
`12/1998 Yanagihara ............................. 386/109
`FOREIGN PATENT DOCUMENTS
`0 049 652
`4/1982 European Pat. Off.
`.
`OTHER PUBLICATIONS
`
`Riemann U: “Der MPEG—2—Standard Generische Codi-
`
`erung fur Bewegtbilder und Zugehoriger Audio—Informa-
`tion. Multiplex—Spezifikation for die Flexible Ubgertragung
`Digitaler Datenstrome” Fernseh und Kinotechnik, vol. 48,
`N0. 10, Oct. 1, 1994, pp. 545—550, 553, XP000468290.
`Riemann U: “Der MPEG—2—Standard. Multiplex—Spezifika-
`tion Fur Die Flexible Ubertragung Digitaler Datenstrome”
`Fernseh Und Kinotechnik, vol. 48, N0. 9, Sep. 1, 1994, pp.
`460—462, 464—468, XP000468751.
`
`Primary Examiner—W. Chris Kim
`Attorney, Agent, or Firm—Frommer Lawerence & Haug,
`LLB; William S, Frommer
`
`[57]
`
`ABSTRACT
`
`.A dlglm VTR IS capable 0f repmdllcmg a recorded pm?“
`image in a normal mode and a variable speed reproduction
`mode. During normal speed reproduction, the digital VTR
`reproduces a recorded picture from data that has been
`mwmwmammmlhzmmdamwmmimmmIWMH
`p y
`g
`the digital VTR is in a Variable 10W Speed reproduction
`mode, it reproduces a picture from data recorded in a first
`trick play area. When the digital VTR is in a variable high
`speed reproduction mode, it reproduces a picture from data
`recorded in a second trick play area. The first and second
`triek Play areas are located at respectiVe traeks that C0rre-
`Spond to different azimuths.
`
`26 Claims, 18 Drawing Sheets
`
`
`RATE
`
`CONVERTING
`
`
`BUFFER
`
`
`
`SB FORMATTER
`
`TS/PES
`DECODER
`
`5T
`
`53
`
`54
`
`START CODE
`ANALYZING
`
`
`
`
`
`
`
`
`
`TP PROCESSING
`
`55
`
`56A
`
`
`
` TS/PES
`PACKET
`
`FORMING
`
`
` TS/PES
`
`PACKET
`FORMING
`
`
`57A
`
`TPI
`BUFFER
`
`5TB
`
`TP2
`BUFFER
`
`59B
`
`SB FORMATTER
`
`
`
`59C
`
`SB FORMATTER
`
`Page 1 of 28
`
`OPENTV EXHIBIT 2010
`
`NETFLIX, INC. v. OPENTV, INC.
`
`IPR2014-00252
`
`

`

`US. Patent
`
`Feb. 22,2000
`
`Sheet 1 0f 18
`
`6,028,726
`
`Fig.
`
`1 C
`
`CODER
`
`HANNEL
`
`Fig. 2
`
`1
`
`I 1
`1 8 8
`
`TIME
`
`INFORMATION
`
`Page 2 of 28
`
`

`

`US. Patent
`
`Feb. 22,2000
`
`Sheet 2 0f 18
`
`6,028,726
`
`Fig. 3
`
`TIME STAMP
`
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`
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`
`Page 3 of 28
`
`

`

`US. Patent
`
`Feb. 22,2000
`
`Sheet 3 0f 18
`
`6,028,726
`
`N0 MAL PL
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`AREA
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`
`EFFECTIVE DATA / STUFF DATA (DUMMY)
`
`POLARITY INVERSION
`
`Tst BYTE:
`
`Page 4 of 28
`
`

`

`US. Patent
`
`Feb. 22, 2000
`
`Sheet 4 0f 18
`
`6,028,726
`
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`
`
`
`Page 5 of 28
`
`
`

`

`US. Patent
`
`Feb. 22,2000
`
`Sheet 5 0f 18
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`6,028,726
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`Page 6 of 28
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`US. Patent
`
`Feb. 22, 2000
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`Sheet 7 0f 18
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`Page 8 of 28
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`US. Patent
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`Feb. 22, 2000
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`US. Patent
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`Feb. 22, 2000
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`US. Patent
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`Feb. 22, 2000
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`US. Patent
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`US. Patent
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`Feb. 22,2000
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`US. Patent
`
`Feb. 22,2000
`
`Sheet 16 0f 18
`
`6,028,726
`
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`
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`
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`Page 17 of 28
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`

`US. Patent
`
`Feb. 22, 2000
`
`Sheet 18 0f 18
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`
`

`

`6,028,726
`
`1
`DIGITAL DATA RECORDING/
`REPRODUCING APPARATUS AND METHOD
`WITH MEANS FOR ADDING ARRIVAL TIME
`TO A DATA PACKET
`
`This application is a continuation of application Ser. No.
`08/556,492, filed Nov. 13, 1995, now abandoned.
`
`FIELD OF THE INVENTION
`
`This invention relates to a variable speed recording and
`reproducing system for use in a digital VTR, and in
`particular, to a variable speed recording and reproducing
`system that performs a data rate conversion on program data
`prior to recording and that reconstructs the original time
`base information of the rate converted program during
`reproduction. The variable speed recording and reproducing
`system of the present invention is particularly suitable for
`recording video signals that are organized in accordance
`with the MPEG2 format.
`
`10
`
`15
`
`20
`
`BACKGROUND OF THE INVENTION
`
`2
`which either additional identifying information or dummy
`bytes can be inserted.
`As shown in FIG. 22C, the adaptation field is composed
`of several codes. The first code is an adaptation field length
`code that indicates the data length of the adaptation field.
`The next code is a discontinuous indicator code that changes
`its contents to indicate that a system clock has been reset.
`Following the discontinuous indicator code is a random
`access indicator code that
`indicates an entry point
`for
`random access. The random access indicator code is fol-
`lowed by a priority stream elementary indicator code that
`designates a portion or the entirety of the payload portion as
`important. The final portion of the adaptation field is des-
`ignated as an optional field.
`As shown in FIG. 22D, the optional field is composed of
`several codes. These codes are a PCR, an OPCR, a splice
`count down, a transport private data length and transport
`private data, an adaptational field extension length, and an
`optional field. The PCR code includes a time stamp for
`setting and calibrating a time value. A Phase Locked Loop
`(PLL) uses the PCR code to generate a system clock of 27
`MHZ, for instance. In order to accurately decode and repro-
`duce the program data, the corresponding time base stored
`in the PCR field must be maintained with as little deviation
`
`25
`
`as possible.
`FIGS. 23A and 23B illustrate the manner in which an
`
`is recorded by the previously
`MPEG2 transport packet
`proposed digital VTR. A desired program (for example,
`program A) is selected from a time-division multiplexed
`data stream of programs A, B, and C. Assuming that a data
`rate of programs A, B, and C is equal to, for example, 30
`Mbps and a substantial rate of the selected program is equal
`to 10 Mbps, a rate conversion from 30 Mpbs to 10 Mbps is
`executed in a rate converting buffer.
`FIG. 24 illustrates such a rate converting buffer 102. The
`transport packet of the selected program is supplied to an
`input terminal 101 of rate converting buffer 102, which
`reduces the input program data rate to 1/3 of its original value.
`Thus, the rate is reduced from 30 Mbps to 10 Mbps. The rate
`converted transport packet is supplied from an output ter-
`minal 103 to a digital VTR.
`Since a recording rate in the SD mode of the digital VTR
`is equal to 25 Mbps, by performing the rate conversion as
`mentioned above, the transport packet can be recorded as it
`is by the digital VTR.
`By performing the above-discussed rate conversion to the
`selected program,
`the previously proposed digital VTR
`system also changes the time base of the selected program.
`Nevertheless, since the PCR code of the selected program
`still reflects the time base of the program before it was rate
`converted, a subsequent decoding operation that relies on
`this inaccurate PCR code will result in a poor reproduction
`of the rate-converted video signal.
`The MPEG2 format provides for three frames of data: an
`I frame which was intra-frame encoded, a P frame which
`was forward direction prediction encoded, and a B frame
`which was bi-directionally prediction encoded. In a variable
`speed reproducing mode, since the reproducing head does
`not traverse the entire length of each track, the data of the
`continuous frames cannot be obtained. Thus, the data of the
`P and B frames cannot be decoded. Only the data of the I
`frame which was intra-frame encoded can be decoded.
`
`Therefore, only the data of the I frame is used in the variable
`speed reproducing mode of the previously proposed digital
`VTR system.
`However, when the transport packet is supplied to the
`digital VTR for recording, the packets that include the I
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`In a previously proposed digital VTR, a digital video
`signal
`is recorded onto a magnetic tape after it
`is first
`compressed in accordance with a DCT (Discrete Cosine
`Transform) technique and recorded in accordance with a
`variable length encoding technique. Such a digital VTR is
`capable of recording video signals in two different modes. In
`a first mode, the digital VTR records the well-known NTSC
`television broadcast signal, or the like. This mode is referred
`to herein as an SD mode,
`in which the video signal is
`recorded at a rate of 25 Mbps. In a second recording mode,
`the digital VTR records an HDTV signal. This second mode
`is referred to herein as the HD mode, in which the video
`signal is recorded at a rate of 50 Mbps. Techniques for
`recording what is referred to as a transport packet, which is
`formatted as an MPEG2 signal, are currently being pro-
`posed.
`The MPEG2 format allows a plurality of different pro-
`grams to be transmitted as a time division multiplexed
`encoded data stream. The fundamental data structure for
`
`organizing and conveying these multiplexed programs to
`their respective destinations is referred to as a transport
`packet.
`Each transport packet has a fixed length of 188 bytes, and
`it comprises a header portion and a payload portion. The data
`of the header portion identifies the content of the transport
`packet. The digital VTR uses this header portion to select a
`designated program from the multiplexed program data
`stream.
`
`FIGS. 22A—22D illustrate the contents of the transport
`packet. As shown in FIG. 22A, every transport packet
`includes a header portion followed by a payload portion. The
`payload portion corresponds to the contents of the video
`program. As shown in FIG. 22B, the header comprises: a
`sync code of eight bytes; a transport error indicator which
`indicates the presence or absence of errors in a packet; a
`payload unit start indicator which indicates the start of a
`payload unit; a transport priority code which indicates the
`importance of a corresponding packet; a packet identifica-
`tion (PID) code which indicates a particular attribute of the
`packet; a transport scramble control code which indicates
`whether the data of the payload portion has been scrambled;
`an adaptation field control code which indicates the presence
`or absence of an adaptation field; a cyclic counter that
`determines whether a part of the packet has been abandoned
`midway during transmission; and an adaptation field to
`
`Page 20 of 28
`
`

`

`6,028,726
`
`3
`frame cannot be obtained entirely in the variable speed
`reproducing mode. Apositional relation in which the data of
`the I frame has been recorded is uncertain. Therefore, the
`data of the I frame corresponding to a specific portion of a
`picture plane is dropped out at the time of the variable speed
`reproduction and a picture quality in the variable speed
`reproducing mode deteriorates.
`
`OBJECTS AND SUMMARY OF THE
`INVENTION
`
`It is, therefore, an object of the invention to provide a
`digital data recording/reproducing apparatus and method
`which can correctly reconstruct a time base of an original
`transport packet from a transport packet
`that has been
`recorded as a rate converted signal.
`Another object of the invention is to provide a digital data
`recording/reproducing apparatus and method that uses a
`variable speed reproduction mode, which does not degrade
`the quality of a picture reproduced from data of a rate
`converted transport packet.
`Still another object of the invention is to provide a digital
`data recording apparatus that comprises a time generating
`means for determining on the basis of a reference clock
`when a data packet is received, and means for time stamping
`the received data packet with this arrival time.
`A further object of the invention is to provide a digital
`data reproducing apparatus for reproducing a data packet
`recorded on a tape, characterized in that a time base is
`managed on the basis of an arrival time added to the data
`packet.
`Another object of the invention is to provide a digital data
`recording apparatus for recording a data packet onto a tape,
`in which the apparatus comprises means for organizing the
`track on the tape into a normal play area and a trick play
`area. The trick play area is located at various reproducible
`areas on the track that the head traces when the apparatus is
`in a maximum variable reproducing speed mode. The appa-
`ratus also includes means for recording the data packet into
`the normal play area and for recording into the trick play
`areas during variable speed reproduction a portion of the
`data packet. The apparatus further includes means for repro-
`ducing the data recorded in the normal and trick play areas.
`When a program is selected from the transport packet and
`is rate converted and recorded, the arrival time information
`of the packet is added to each packet in order to reconstruct
`the time base information of each packet. This time infor-
`mation is generated on the basis of a reference clock. Upon
`reproduction, the same time base state as that upon inputting
`is reconstructed on the basis of the time information.
`
`As for the packets to which the time information was
`added, the relation between the number of sync blocks and
`the number of packets in which sync blocks are recorded is
`set to an integer ratio.
`In the recording and reproduction of the digital VTR,
`since the rotation of the drum is synchronized with the
`reference clock,
`the time base information of the data
`packets can be preserved during recording and reproduction.
`The present invention uses two trick play areas; they are
`designated TP1 and TP2. Trick play area TP1 is used during
`high speed variable speed reproduction, and trick play area
`TP2 is used during low speed variable speed reproduction.
`Trick play areas TP1 and TP2 are arranged in tracks of
`different azimuths, respectively. The data of the I frame is
`recorded in the trick play areas TP1 and TP2. By using the
`data recorded in the trick play areas TP1 and TP2, the picture
`
`10
`
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`quality can be improved during variable speed reproduction.
`Furthermore, the operation of the present invention is not
`constrained by any particular recording head arrangement
`because the trick play areas are each arranged in tracks of
`different azimuths, respectively, and because only the tracks
`corresponding to one azimuth (and to one of the trick play
`areas) is used either in the low or high speed variable speed
`reproduction mode.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The following detailed description, given by way of
`example and not intended to limit the present invention
`solely thereto, will best be understood in conjunction with
`the accompanying drawings in which:
`FIG. 1 illustrates a digital VTR recording system of the
`present invention;
`FIG. 2 illustrates the data format of a transport packet;
`FIG. 3 illustrates a circuit for adding the time information
`to a transport packet;
`FIG. 4 illustrates a plurality of transport packets organized
`into a plurality of sync blocks;
`FIG. 5 illustrates the format of the extra header that is
`
`added to each sync block;
`FIG. 6 illustrates the track locations of a plurality of trick
`play areas;
`FIG. 7 illustrates a waveform diagram for explaining the
`trick play area;
`FIG. 8 illustrates the data format of an oblique track used
`in the present invention;
`FIG. 9 illustrates the location of a plurality of trick play
`areas in relation to a plurality of pilot signals;
`FIG. 10 illustrates the various tape speeds that can be
`realized during a variable speed reproduction mode.
`FIG. 11 shows the path of a reproducing head during a
`variable speed reproducing operation;
`FIGS. 12A and 12B illustrate the portions of each track
`that are traced by each scanning operation in a variable
`speed reproduction operation;
`FIGS. 13A and 13B show an arrangement of sync blocks
`in each recording track;
`FIG. 14 illustrates a first embodiment of a recording
`apparatus that records variable speed reproduction data into
`trick play areas;
`FIG. 15 illustrates a second embodiment of a recording
`apparatus that records variable speed reproduction data into
`trick play areas;
`FIG. 16 is a graph that illustrates a relationship between
`the amount of high frequency coefficients in the variable
`speed recording data and the corresponding memory size
`(expressed in bits) needed to store such recording data;
`FIG. 17 illustrates a third embodiment of an apparatus for
`recording variable speed reproduction data into trick play
`areas;
`
`FIG. 18 illustrates a procedure for dividing a picture
`plane;
`FIG. 19 illustrates a fourth embodiment of an apparatus
`for recording variable speed reproduction data into trick play
`areas;
`
`FIG. 20 is a diagram for explaining the dividing of the
`picture plane;
`FIG. 21 illustrates a digital VTR reproducing system of
`the present invention;
`FIGS. 22A—22D are schematic diagrams for use in expla-
`nation of the transport packet;
`
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`6,028,726
`
`5
`FIGS. 23A and 23B illustrate the selection of one trans-
`
`port packet program for recording from a plurality of
`multiplexed programs; and
`FIG. 24 illustrates a rate converting buffer for use in the
`present invention.
`
`DETAILED DESCRIPTION OF INVENTION
`
`FIG. 1 illustrates a recording system of a digital VTR
`Reference numeral 1 denotes an input terminal for receiving
`an analog video signal, such as an NTSC television signal or
`the like. For purposes of this discussion, this video signal
`will be referred to as a standard video signal. This video
`signal is supplied to an A/D converter 2 which converts the
`received analog video signal to a digital video signal.
`A/D converter 2 supplies the converted video signal to a
`DCT compressing circuit, which compresses the input video
`signal in accordance with a DCT compression technique and
`variable length encoding. In particular, the video signal from
`the A/D converter 2 is divided into blocks which are shuffled
`and subjected to the DCT conversion. The DCT converted
`data is buffered on a predetermined buffer unit basis. The
`DCT compressing circuit employs a buffer unit in accor-
`dance with a quantization table such that the total code
`amount is equal to or less than a predetermined value. The
`data is quantized by such an optimum quantization table and
`is variable length encoded and is framed.
`The output of DCT compressing circuit 3 is then supplied
`to terminal 4B of switching circuit 4. Switch 4 also includes
`terminal 4A, to which a digital video signal transport packet
`encoded in the MPEG2 format is supplied after this signal is
`rate converted by rate converting and format converting
`circuit 9.
`
`The rate conversion and format converting unit 9 converts
`the rate of the MPEG2 signal from, for example, 30 Mbps
`to 10 Mbps. Further the data in the trick play areas (which
`will be explained later) is arranged in order to obtain a
`preferable picture plane upon variable speed reproduction.
`The recording system of FIG. 1 sets the switching circuit 4
`to terminal 4B in order to record the video signal supplied
`to input terminal 1; when the system records the MPEG2
`transport packet, it sets the switching circuit to terminal 4A.
`The output of the switching circuit 4 is supplied to a frame
`forming circuit 5, which organizes the recording data into
`predefined frames and executes an error correction coding
`process.
`
`The output of the frame forming circuit 5 is supplied to a
`channel coder 6, which modulates the received data. The
`channel coder 6 supplies the modulated signal to a rotary
`head 8 through a recording amplifier 7. The compressed
`video signal or the transport packet of the MPEG2, depend-
`ing on which switching terminal the switching circuit 4 was
`set to, is recorded on a magnetic tape by the rotary head 8.
`When the MPEG2 transport packet is to be recorded,
`switching circuit 4 is switched to terminal 4A. By doing so,
`the MPEG2 transport packet is divided into frames by frame
`forming circuit 5, modulated by channel coder 6, and
`recorded onto the magnetic tape by rotary head 8.
`When the standard video signal is to be recorded, switch-
`ing circuit 4 is switched to terminal 4B. By doing so, the
`standard video signal is compressed by DCT compressing
`circuit 3, divided into frames by frame forming circuit 5,
`modulated by channel coder 6, and recorded onto the
`magnetic tape by rotary head 8.
`As mentioned above, recording an MPEG2 transport
`packet signal first requires rate converting and format con-
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`verting circuit 9 to select a program (encoded in the MPEG2
`format) from the plurality of time division multiplexed
`programs that normally are supplied thereto, for recording
`on a record medium (e.g., a magnetic tape). This circuit then
`converts the data rate of the selected program from, for
`example, 30 Mbps to 10 Mbps. The rate conversion also
`alters the time base information of the MPEG2 program.
`Thus, upon reproduction the original time base information
`of the recorded MPEG2 program cannot be retrieved from
`the program itself because of this rate conversion.
`In order to remedy this situation, the present invention
`adds to each transport packet time information that indicates
`the packet arrival time. This addition is made before each
`transport packet is supplied to the rate converting and format
`converting circuit 9 for recording on the record medium. The
`added time information is recorded onto the magnetic tape
`along with each transport packet. During reproduction of the
`recorded transport packets, the system of the present inven-
`tion extracts each packet’s associated time information in
`order to obtain each packet’s original time base information.
`FIG. 2 illustrates the data format of a transport packet and
`the associated time information. As stated with respect to
`FIGS. 17A and 17B, prior to rate conversion, each header of
`every transport packet begins with a sync code of 8 bytes. In
`order to provide space for the time information, which
`comprises 3 bytes, the rate converting and format converting
`circuit 9 removes one byte from the sync code and adds the
`three byte time information code to the beginning of the
`header portion. Thus, after this procedure is accomplished,
`each transport packet will comprise 190 bytes.
`FIG. 3 illustrates a circuit for adding the time information
`of three bytes before the transport packet is recorded. In FIG.
`3, the transport packet is first supplied to sync detecting
`circuit 32. The sync detecting circuit 32 detects the sync
`code at the head of the transport packet. A detection output
`of the sync detecting signal is supplied to latch 33. A second
`output of the sync detecting circuit 32 is supplied to a sync
`eliminating circuit 37. When the sync code is detected, the
`sync eliminating circuit 37 eliminates one byte of the sync
`code. An output of the sync eliminating circuit 37 is then
`supplied to a time stamp circuit 38.
`A reference clock generator 34 generates a reference
`clock with a frequency of, for example, 27 MHz. This
`reference clock signal is supplied to a Phase Locked Loop
`(PLL) 35 and to a counter 36. The drum to which the head
`8 is attached is rotated at, for example, 150 Hz on the basis
`of the output of the PLL 35.
`The reference clock signal is counted by the counter 36,
`from which time information is derived. This derived time
`
`information is supplied to latch 33. The time stamp circuit 38
`adds the 3 bytes of time information to the transport packet
`and supplies this modified packet to output terminal 39 for
`recording.
`FIG. 4 illustrates the data organization of two transport
`packets, each one including a time stamp of 3 bytes as
`indicated by the darkly shaded blocks. These two transport
`packets are organized into 5 sync blocks SBO—SB4. An extra
`header, indicated by the lightly shaded blocks, is added to
`each sync block. The solid lines indicate the transport
`packets. Each extra header includes a serial number, or the
`like. The dotted lines in FIG. 4 indicate a sync and ID code
`(added to the beginning of each sync block), and a parity
`(C1) code (added to the end of each sync block). Thus, each
`sync block begins with the sync and ID code of 5 bytes. The
`next 72 bytes of each sync block (including the extra header)
`comprises the payload portion of the sync block. Each sync
`block then concludes with a parity (C1) code of eight bytes.
`
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`6,028,726
`
`7
`FIG. 5 illustrates in more detail the extra header added to
`
`each sync block. As indicated in FIG. 5, the extra header can
`be divided into a normal play area and a trick play area.
`These extra header bytes can include both data that
`is
`representative of a particular value (effective data) and data
`with no significance other than its ability to fill empty space
`(dummy data). Each extra header can include data relating
`to the identity of its corresponding sync block (serial
`number), polarity inversion data, normal play (NP) data, or
`trick play (TP) data. Aportion of the extra header can be set
`aside as a reserved area.
`
`The trick play area of the present invention is intended to
`improve the picture quality in the variable speed reproduc-
`ing mode by serving as a reproducible area during variable
`speed reproduction. With respect to the MPEG2 format,
`which provides an I frame, P frame, and B frame, during
`variable speed reproduction, only the I frame data is used,
`and this I frame data is stored in the trick play area.
`Namely, the recording rate of the digital VTR is set to 25
`Mbps in the SD mode. On the other hand, when the transport
`packet is recorded at the rate of 10 Mbps, there is a surplus
`recording rate. Therefore, the reproducible area in the vari-
`able speed reproducing mode can be set to the trick play area
`and the packet including the I frame can be overlappingly
`recorded into the trick play area.
`For example, FIG. 6 shows the locus of a head as it passes
`over a plurality of recording tracks during the variable speed
`reproducing mode. The path of the head is illustrated in FIG.
`6 as the arrow that extends diagonally across the plurality of
`tracks. Each shaded portion along this diagonal arrow cor-
`responds to a trick play (TP) area. The reproducible area TP
`is used as the trick play area to record the packet for variable
`speed reproduction. In a VTR that uses helical scan and
`azimuth recording, the data that is reproduced from the TP
`area resembles a burst-like shape as shown in FIG. 7. By
`fixing the track-shaped positions in the reproducible area TP
`by an ATF (Automatic Track Following) operation, or the
`like, and recording the packet including the I frame into the
`reproducible area, the data of the I frame can be accurately
`reproduced.
`According to an embodiment of the invention, two kinds
`of trick play areas, TP1 and TP2, are provided. One trick
`play area (TP1) is used for variable speed reproduction of a
`high speed. The other trick play area (TP2) is used for
`variable speed reproduction of a low speed. The trick play
`areas TP1 and TP2 are respectively provided in tracks of
`different azimuth angles.
`Namely, in the digital VTR, as shown in FIG. 8, each track
`is divided into four sectors: an ITI sector, which is used for
`post-recording operations or the like; an audio sector; a
`video sector; and a subcode sector, which is used during
`search operations or the like. The track is traced by heads of
`different azimuth angles. For example, two rotary heads may
`be arranged 180° apart, or a single head assembly with
`double azimuths can be used. Apilot signal is superimposed
`onto the track in order to permit ATF tracking.
`FIG. 9 illustrates two types of trick play areas, designated
`as TP1 and TP2, and their locations with respect to pilot
`signals f0 and f1. The video sectors of the tracks are
`alternately assigned pilot signals f0 or f1. Pilot signal f0 is
`incorporated within trick play area TP1, which the system of
`the present invention uses during high speed variable speed
`reproduction. Such high speed reproduction can occur, for
`example, at 18-times the normal reproduction speed. In the
`example of FIG. 9, data is respectively recorded 18 times in
`TP1. Pilot signal f1 is incorporated within trick play area
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`TP2, which the system uses during low speed variable speed
`reproduction. Such low speed reproduction can occur, for
`example, at 4-times the normal reproduction speed. In trick
`play area TP2, data is repetitively recorded twice.
`As mentioned above, the trick play areas TP1 and TP2 are
`arranged in the tracks of different azimuths, respectively. By
`using only the track of one azimuth in each of the trick play
`areas TP1 and TP2, the variable speed reproduction can be
`performed by using two heads arranged 180° apart, in a
`double-azimuth head arrangement without limiting the head
`construction.
`
`During a phase lock operation of the digital VTR, tracking
`information is obtained from the tracks that include pilot
`signal f0. By relying on pilot signal f0 to obtain tracking
`information, the digital VTR renders the tracks with pilot
`signal f1 vulnerable to inaccuracies that may result from
`errors in mounting the heads to the rotating drums. To
`eliminate this vulnerability,
`the trick play area TP2 is
`arranged in the tracks that are associated with pilot signal f1.
`The trick play area TP1 for variable speed reproduction of
`the high speed is assigned to the tracks that are associated
`with pilot signal f0. The trick play area TP1 compensates for
`tracking deviations caused by the 4-times speed reproduc-
`tion mode. These tracking deviations are larger than those
`caused