Recording apparatus, recording/reproducing apparatus and recording method

A recording apparatus for storing input video and audio data temporarily in a memory, reading out back the video and audio data from the memory and recording the video and audio data into a recording medium wherein a storage-size of the memory is found and video data to be stored in the memory is thinned in accordance with the storage-size so that audio data of a minimum required amount can be stored in the memory to prevent continuity of audio data recorded in the recording medium from becoming unsustainable.

BACKGROUND OF THE INVENTION
 The present invention relates to a recording apparatus, a
 recording/reproducing apparatus and a recording medium capable of
 recording video-signal data and audio-signal data into a recording medium
 of a predetermined type, being well applicable to equipment such as a
 video camera.
 At the present time, a video camera of a portable type, wherein an image
 shooting apparatus such as a camera and a video deck capable of recording
 and playing back video and audio data are integrated into a single body,
 is becoming widely popular.
 In general, such a video camera employs a removable recording medium
 represented mainly by a videotape cassette. Normally, when the storage
 area of a recording medium mounted on the main body of such a video camera
 is almost all used up in the course of recording carried out by the user
 by utilizing the video camera, the recording is suspended temporarily, the
 recording medium mounted on the video camera is taken out, a new recording
 medium prepared in advance is mounted in place of the removed recording
 medium and the recording is resumed.
 By the way, for example, during a period of time to replace a recording
 medium mounted on the video camera with another one in the course of the
 image shooting as described above, data can not be recorded into the
 recording medium. That is to say, when recording is carried out over a
 long period of time using a plurality of recording media, information that
 would be recorded into a recording medium during a period of time to
 replace the recording medium mounted on the video camera with another one
 is lost. As a result, continuity of recorded data along the time axis
 between 2 recording media can not be obtained in a strict sense.
 Particularly, in recent years, promotion of efforts to increase the
 recording density of the disc recording medium is under way. With such
 promotion serving as a background, a video deck capable of recording and
 playing back video and audio data can be possibly employed in a video
 camera for a disc recording medium. If a disc recording medium is employed
 as a recording medium, operations such as random accesses can be carried
 out, so that, during playback processing for example, operations such as a
 scan, forward and rewind can be implemented at a higher speed.
 In the present state of the art, however, a disc recording medium generally
 has a small storage capacity in comparison with a tape recording medium as
 before. In the case of a video camera in particular, the amount of video
 data of a moving picture is extremely large in comparison with information
 to be recorded such as audio data. Thus, in a video camera system
 employing a disc as a recording medium, the recording time per disc is
 expected to be relatively short. As a result, there are raised problems
 that, in the course of recording over a long period of time, the disc
 recording medium must be replaced more frequently and a ratio of time of
 losing data caused by replacement of the disc recording medium to the
 total recording time increases accordingly.
 In addition, as is generally known, a recording/playback apparatus for
 driving a disc recording medium is generally more sensitive to vibration
 and shocks than a driver for driving a tape recording medium.
 For this reason, when a variety of servo of a driver employed in a video
 camera for driving a disc used in the camera as a recording medium is out
 of control due to a cause such as vibration of the main body of the camera
 or a shock given to the main body during a recording operation using the
 camera for example, recording of data is interrupted. In such a
 circumstance, it is more certainly within the bounds of probability that
 continuity of recorded data along the time axis can not be obtained any
 more.
 SUMMARY OF THE INVENTION
 It is thus an object of the present invention addressing the problems
 described above to provide more convenience to the user of a video camera
 by sustaining as much continuity of recorded data between recording media
 along the time axis as possible even for a circumstance wherein recording
 of data into a recording medium employed in the camera can not be carried
 out physically due to, for example, replacement of the recording medium by
 another one in the course of recording using the camera.
 In order to solve the problems described above, the present invention
 provides a recording apparatus characterized in that the apparatus
 comprises: a video compressing means for compressing input video data; an
 audio compressing means for compressing input audio data; a storage means
 for storing compressed video data generated by the video compressing means
 and compressed audio data generated by the audio compressing means; a
 recording means for reading out compressed video data and audio data
 temporarily stored in the storage means back from the storage means with
 predetermined timing and then recording the compressed video and audio
 data read out from the storage means into a recording medium; a
 storage-size detecting means for finding a storage-size of the storage
 means; and a storage-means control means for writing compressed audio data
 generated by the audio compressing means to be supplied to the storage
 means into the storage means at a priority higher than compressed video
 data generated by the video compressing means to be supplied to the
 storage means in accordance with a storage-size of the storage means found
 by the storage-size detecting means.
 In addition, the present invention also provides a recording/reproducing
 apparatus characterized in that the apparatus comprises: a video
 compressing means for compressing input video data; an audio compressing
 means for compressing input audio data; a storage means for storing
 compressed video data generated by the video compressing means and
 compressed audio data generated by the audio compressing means; a
 storage-size detecting means for finding a storage-size of the storage
 means; a control means for controlling the video compressing means to thin
 compressed video data generated by the video compressing means in
 accordance with a storage-size of the storage means found by the
 storage-size detecting means so as to reserve an area in the storage means
 large enough for storing compressed audio data produced by the audio
 compressing means to be supplied to the storage means; an identifier
 generating means for generating an identifier used for identifying a
 control state of the control means; a recording means for reading out
 compressed video data, compressed audio data and the identifier generated
 by the identifier generating means to identify a control state of the
 control means temporarily stored in the storage means back from the
 storage means with predetermined timing and then recording the compressed
 video data, the compressed audio data and the identifier read out from the
 storage means into a recording medium; a reproducing means for reproducing
 compressed video data, compressed audio data and the identifier
 identifying a control state of the control means from the recording
 medium; a video decompressing means for decompressing compressed video
 data reproduced by the reproducing means; an audio decompressing means for
 decompressing compressed audio data reproduced by the reproducing means;
 and a video-decompressing-means control means for controlling
 decompression carried out by the video decompressing means in accordance
 with the identifier reproduced by the reproducing means.
 Furthermore, the present invention also provides a recording method
 characterized in that the method comprises the steps of: compressing input
 video data; compressing input audio data; storing compressed video data
 and compressed audio data in a memory; finding a storage-size of the
 memory; writing compressed audio data supplied to the memory at a priority
 higher than compressed video data supplied to the memory in accordance
 with the storage-size of the memory; and reading out compressed video data
 and compressed audio data temporarily stored in the memory back from the
 memory with predetermined timing and then recording the compressed video
 and audio data read out from the memory into a recording medium.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 A recording apparatus implemented by an embodiment of the present invention
 is explained by referring to FIGS. 1 to 10. To be more specific, the
 embodiment implements a video camera of a portable type, wherein an image
 shooting apparatus and a recording/reproducing apparatus capable of
 recording and playing back video and audio data are integrated into a
 single body. The recording/reproducing apparatus mounted on the video
 camera provided by the embodiment is designed to execute functions of
 recording and playing back data into and from a so-called Mini Disc
 (trademark).
 The video camera is explained in the following order.
 1. Disc Format
 2. Configuration of the Video Camera
 3. Configuration of a Media Drive Unit
 4. Operations in Stretched-Recording mode
 4-1. Writing Data into a Buffer Memory
 4-2. Recording of Additional Information
 5. Processing Operations
 6. Playback Operation
 1. Disc Format
 The recording/reproducing apparatus mounted on the video camera provided by
 the embodiment is designed to execute functions of recording and playing
 back data having a so-called MD-data format into and from a mini disc.
 There have been developed two kinds of MD-data format, namely, MD-DATA1
 and MD-DATA2. The video camera provided by this embodiment carries out
 recording and playback operations in the MD-DATA2 format which allows a
 recording operation to be performed at a recording density higher than
 MD-DATA1. For this reason, first of all, disc format of the MD-DATA2 is
 explained.
 FIGS. 1 and 2 are diagrams each conceptually showing a typical structure of
 a track on a disc with the MD-DATA2 format. FIG. 2 is a diagram showing an
 enlarged cross section view of a portion enclosed by a dotted line A shown
 in FIG. 1.
 As shown in these figures, on the surface of the disc, there are created
 two kinds of groove in advance, namely, a wobbled groove (WG) having
 wobble and a non-wobbled groove (NWG) with no wobble. Wobbled groove WG
 and non-wobbled groove NWG form double spirals on the disc which sandwich
 land Ld therebetween.
 In the MD-DATA2 format, land Ld is used as a track. Since land Ld is
 provided between wobbled groove WG and non-wobbled groove NWG, there are
 two kinds of track, namely, tracks Tr.cndot.A and Tr.cndot.B. Tracks
 Tr.cndot.A and Tr.cndot.B are provided independently of each other,
 forming double spirals. To put it in detail, wobbled groove WG is located
 on the disc-outer-circumference side of track Tr.cndot.A and non-wobbled
 groove NWG is located on the disc-inner-circumference side of track
 Tr.cndot.A. On the other hand, non-wobbled groove NWG is located on the
 disc-outer-circumference side of track Tr.cndot.B and wobbled groove WG is
 located on the disc-inner-circumference side of track Tr.cndot.B. That is
 to say, wobble is provided only on the disc-outer-circumference side of
 track Tr.cndot.A and on the disc-inner-circumference side of track
 Tr.cndot.B.
 In this case, a track pitch is a distance between the center of track
 Tr.cndot.A and the center of track Tr.cndot.B adjacent each other. The
 track pitch has a value of 0.95 .mu.m as shown in FIG. 2.
 Creation of the wobble on wobbled groove WG is based on a signal
 experiencing FM modulation and bi-phase modulation of encoded physical
 addresses on the disc. For this reason, by demodulating the reproducing
 information obtained from the wobbling provided on wobbled groove WG, a
 physical address on the disc can be extracted.
 Address information included in wobbled groove WG is valid information
 common to tracks Tr.cndot.A and Tr.cndot.B. That is to say, track
 Tr.cndot.A on the disc-inner-circumference side of wobbled groove WG and
 track Tr.cndot.B on the disc-outer-circumference side of wobbled groove WG
 sandwiching wobbled groove WG share address information included in the
 wobble provided on wobbled groove WG. It should be noted that such an
 addressing system embraced by this embodiment is referred to as an
 interlace addressing system. By adoption of the interlace addressing
 system, for example, cross-talk between adjacent wobbled grooves can be
 suppressed and the track pitch can be reduced. A system wherein an address
 is recorded in wobble created on a groove is referred to as an ADIP
 (Address in Pregroove) system.
 As described above, tracks Tr.cndot.A and Tr.cndot.B share the same address
 information. The following is a description of how to recognize which of
 the tracks is being traced.
 Typically, a three-beam system is adopted. In this system, with a main beam
 used for tracing a track, that is, land Ld, the two remaining side beams
 are tracing the two grooves on both sides of the track.
 In the example shown in FIG. 2, main-beam spot SPm is tracing track
 Tr.cndot.A. In this case, side-beam spot SPs1 on the
 disc-inner-circumference side is tracing non-wobbled groove NWG of track
 Tr.cndot.A while side-beam spot SPs2 on the disc-outer-circumference side
 is tracing wobbled groove WG of track Tr.cndot.A.
 In another tracing state not shown in the figure, while main-beam spot SPm
 is tracing track Tr.cndot.B, side-beam spot SPs1 is tracing wobbled groove
 WG on the disc-inner-circumference side of track Tr.cndot.B and side-beam
 spot SPs2 is tracing non-wobbled groove NWG on the
 disc-outer-circumference side of track Tr.cndot.B.
 As described above, grooves NWG and WG traced by side-beam spots SPs1 and
 SPs2 respectively while main-beam spot SPm is tracing track Tr.cndot.A are
 deliberately swapped with grooves WG and NWG traced by side-beam spots
 SPs1 and SPs2 respectively while main-beam spot SPm is tracing track
 Tr.cndot.B.
 A photo detector detecting a beam reflected from side-beam spot SPs1 or
 SPs2 generates a detection signal with a different waveform which
 indicates whether the side-beam spot is currently tracing wobbled groove
 WG or non-wobbled groove NWG. That is to say, the detection signal can be
 used as a base for determining whether side-beam spot SPs1 or SPs2 is
 currently tracing wobbled groove WG or non-wobbled groove NWG. As a
 result, it is possible to recognize which track of Tr.cndot.A and
 Tr.cndot.B is currently being traced by the main beam.
 FIG. 3 is a table showing comparison of major specifications of the
 MD-DATA2 format having the track structure described above with those of
 the MD-DATA1 format.
 In the first place, according to the MD-DATA1 format, the track pitch is
 1.6 .mu.m, the bit length is 0.5 .mu.m/bit, the laser wavelength .lambda.
 is 780 nm and the numerical aperture NA of the optical head is 0.45.
 A groove recording system is adopted. In the groove recording system, data
 is recorded onto and played back from a groove.
 A wobbled groove is used in an addressing system wherein a groove is
 created as a single spiral and wobble including address information is
 formed on each side of the groove.
 An EFM (Eight-Fourteen modulation) system is adopted as a system for
 modulating data to be recorded and an ACIRC (Advanced Cross Interleave
 Reed-Solomon Code) system is adopted as an error correction technique. A
 convolution type is used in data interleaving. Thus, data redundancy is
 46.3%.
 In the MD-DATA1 format, a CLV (Constant Linear Velocity) technique is
 adopted as a disc driving system. The linear velocity in the CLV technique
 is 1.2 m/s.
 The standard data rate in recording and playback operations is 133 kB/s and
 the storage capacity is 140 B.
 In the MD-DATA2 format, on the other hand, the track pitch is 0.95 .mu.m
 and the bit length is 0.39 .mu.m/bit. Both the track pitch and the bit
 length are obviously smaller than those of the MD-DATAl format. In order
 to implement the bit length described above, the laser wavelength .lambda.
 is set at 650 nm and the numerical aperture NA of the optical head is set
 at 0.52. In this way, the diameter of the beam spot at the focus position
 is reduced and the band of the optical system is widened.
 As having been described by referring to FIGS. 1 and 2, the land recording
 system and the interlace addressing system are adopted.
 As a system for modulating data to be recorded, an RLL (1, 7) system
 suitable for high-density recording, where RLL is an abbreviation for Run
 Length Limited, is adopted. As an error correction method, an RS-PC (Read
 Solomon Product Code) system is adopted and, as a data interleaving
 technique, a block closed type is adopted. As a result of adopting the
 above systems, techniques and methods described above, redundancy of data
 can be suppressed to 19.7%.
 Also in the MD-DATA2 format, a CLV (Constant Linear Velocity) technique is
 adopted as a disc driving system. The linear velocity in the CLV technique
 is 2.0 m/s. The standard data rate in recording and playback operations is
 589 kB/s and a storage capacity of 650 MB can be obtained. A recording
 density four times as high as that of the MD-DATA1 format can be
 implemented.
 In the case of data of a moving picture subjected to an MPEG2 (Moving
 Picture Experts Group II) compression/encoding process in an operation to
 record the moving picture in accordance with the MD-DATA2 format, for
 example, a moving picture of 15 to 17 minutes long can be recorded
 regardless the bit rate of the encoded data. In the case of an
 audio-signal subjected to an ATRAC2 (Adaptive Transform Acoustic Coding 2)
 compression process in an operation to record the data of the audio-signal
 only, an audio-signal of about 10 hours long can be recorded. In
 comparison with ATRAC1 compression, the ATRAC2 compression increases
 compressibility to such a value that the bit rate is 1/2 or 1/4 of that of
 ATRAC1.
 2. Configuration of the Video Camera
 FIGS. 4A, 4B and 4C are diagrams showing front, back and side views of a
 typical external appearance of a video camera provided by the embodiment.
 As shown in FIGS. 4A to 4C, on a front face of a main body 200 of the video
 camera provided by the embodiment, a camera lens 201 having an image
 pickup lens for image shooting and a diaphragm is provided in a posture
 protruding out off the front face. A microphone 202 for picking up audio
 from external sources in the course of image shooting is typically
 provided on the upper surface of the main body 200. Thus, the video camera
 is capable of video-recording pictures taken by the camera lens 201 and
 audio-recording sound picked up by the microphone 202.
 On the rear surface of the main body 200, a display unit 6A, an operation
 unit 7 and a speaker SP are provided. The display unit 6A serves as a
 member for outputting and displaying information such as a shot picture or
 a picture played back by an internal recording/reproducing apparatus. It
 should be noted that, as a display device practically serving as the
 display unit 6A, a liquid-crystal display device is typically employed,
 though not limited to a liquid-crystal display device in particular. The
 display unit 6A is also used for displaying a message described typically
 in terms of characters and figures to notify the user of necessary
 information on the operation of the video camera.
 The operation unit 7 is a panel member provided with a set of keys to be
 used by the user for carrying out a variety of operations. In the case of
 a video camera like this instance, the keys typically include a
 video-recording start key for starting an operation to shoot image, a
 video-recording stop key for ending an operation to shoot image and a
 variety of playback keys such as a playback key, a search key, a forward
 key and a rewind key for carrying out operations to play back data
 recorded on a disc 51. A speaker SP is used for reproducing/outputting
 recorded sound by the internal recording/reproducing apparatus. The
 speaker SP also generates a prescribed audio message such as beep sound.
 On the side surface of the main body 200 of the video camera, a disc slot
 203 and an I/F (Interface) terminal T3 are provided. A disc used as a
 recording medium for the video camera provided by the embodiment is
 inserted into or ejected from the video camera through the disc slot 203.
 The I/F terminal T3 serves as an input/output terminal of an interface for
 exchanging data with typically external data equipment.
 It should be noted that the external appearance of the video camera shown
 in FIG. 4 is typical to the last. In actuality, the external appearance
 can be properly modified in accordance with usage conditions required by
 the video camera implemented by the embodiment.
 FIGS. 5, 5A and 5B are block diagrams showing a typical internal
 configuration of the video camera provided by the embodiment.
 In actuality, a lens block 1 shown in the figure includes typically an
 optical system 11 comprising components such as an image pickup lens and a
 diaphragm. The camera lens 201 shown in the external appearance of FIG. 4
 is included in this optical system 11. The lens block 1 also has an
 auto-focus function for implementing an auto-focus operation of the
 optical system 11 by means of a focus motor 12.
 A camera block 2 includes a circuit for converting a picture light shot
 mainly by the lens block 1 into a digital video-signal.
 To put it in detail, an optical picture of a shooting object passing
 through the optical system 11 is supplied to a CCD (Charge Coupled Device)
 21 of the camera block 2. In the CCD 21, the optical picture is subjected
 to opto-electrical conversion to produce a image shooting signal supplied
 to a sample-hold/AGC (Automatic Gain Control) circuit 22. In the
 sample-hold/AGC circuit 22, the shooting signal supplied by the CCD 21 is
 subjected to gain adjustment and sample-hold processing to shape the
 waveform of the signal. A signal output by the sample-hold/AGC circuit 22
 is supplied to a video A/D converter 23 for converting the signal into
 video-signal digital data.
 Timings of pieces of signal processing carried out by the CCD 21, the
 sample-hold/AGC circuit 22 and the video A/D converter 23 are controlled
 by timing signals generated by a timing generator 24. The timing generator
 24 inputs a clock signal used as a base for generating prescribed timing
 signals. The clock signal is also used in signal processing carried out by
 a data-processing/system control circuit 31 employed in a video-signal
 processing unit 3 to be described later. Thus, the timings of the pieces
 of signal processing carried out by the camera block 2 can be synchronized
 with timing of the signal processing carried out by the video-signal
 processing unit 3.
 A camera controller 25 executes necessary control to properly operate a
 variety of functional circuits employed in the camera block 2 and
 controls, among other things, the auto-focus function, automatic exposure
 adjustment, diaphragm adjustment and zooming operations of the lens block
 1. In the case of auto-focus control, for example, the camera controller
 25 controls the rotational angle of the focus motor 12 on the basis of
 focus-control information obtained in accordance with a predetermined
 auto-focus control system. In this way, the image pickup lens can be
 driven into a just-pint state.
 The video-signal processing unit 3 compresses a digital video-signal
 supplied by the camera block 2 and a digital audio-signal generated from
 sound picked up by the microphone 202, and supplies data obtained as a
 result of the compression to a media drive unit 4 at a later stage as user
 recording data in a recording operation. In a playback operation, on the
 other hand, compressed video-signal data and audio-signal data read out
 from a disc 51 are supplied to the video-signal processing unit 3 by the
 media drive unit 4, that is, compressed and encoded video and audio-signal
 data, is demodulated to produce playback video and audio-signals.
 It should be noted that, as a compression/decompression system of
 video-signal data, the embodiment adopts the MPEG2 (Moving Picture Experts
 Group 2) technique for moving pictures and the JPEG (Joint Photographic
 Coding Experts Group) technique for still-pictures. As for the
 compression/decompression system of audio-signal data, the ATRAC2
 (Adaptive Transform Acoustic Coding) 2 technique is adopted.
 The data-processing/system control circuit 31 employed in the video-signal
 processing unit 3 mainly controls the compression and decompression of
 video-signal and audio-signal data in the video-signal processing unit 3
 and executes processing to input and output data to and from the
 video-signal processing unit 3. Processing to control the entire
 video-signal processing unit 3 including the data-processing/system
 control circuit 31 is carried out by a video controller 38 which is
 implemented typically by a microcomputer. The camera controller 25
 employed in the camera block 2 is capable of communicating with a driver
 controller 46 employed in a media drive unit 4 to be described later
 through typically a bus line which is not shown in the figure.
 In a basic recording operation of the video-signal processing unit 3, the
 data-processing/system control circuit 31 receives video-signal data
 supplied by the A/D converter 23 employed in the camera block 2. In the
 data-processing/system control circuit 31, the input video-signal data is
 supplied typically to a motion detecting circuit 35 to be subjected to
 picture processing such as motion compensation using typically a memory 36
 as a working area. The video-signal data completing the picture processing
 in the motion detecting circuit 35 is then supplied to an MPEG2
 video-signal processing circuit 33.
 In the MPEG2 video-signal processing circuit 33, the video-signal data
 supplied thereto is compressed in accordance with an MPEG2 format with
 typically a memory 34 used as a working area to produce a bit stream,
 strictly speaking, an MPEG2 bit stream, of compressed data of the moving
 picture. In addition, in the MPEG2 video-signal processing circuit 33
 provided by the embodiment, data of still-pictures is extracted from the
 video-signal data of the moving picture and compressed to generate
 compressed data of the still-pictures with the JPEG format. It should be
 noted that, instead of carrying out this compression into the JPEG format,
 regular video data of an I (intra) picture included in the compressed
 video data having the MPEG2 format can be treated as data of a
 still-picture.
 The compressed video-signal data obtained as a result of the compression
 and encoding process carried out by the MPEG2 video-signal processing
 circuit 33 is written into typically a buffer memory 32 at a predetermined
 data transfer rate to be stored therein temporarily.
 The MPEG2 format supports both a CBR (Constant Bit Rate) and a VBR
 (Variable Bit Rate) as an encoding bit rate or a data rate as is generally
 known. Particularly in this embodiment, at least in a stretched-recording
 mode, video-signal data is compressed and encoded at a VBR, that is, at a
 bit rate which is changed in accordance with the size of a free area left
 in the buffer memory 32 as will be described later.
 Audio picked up typically by the microphone 202 is converted by an A/D
 converter 64 employed in a display/video/audio I/O (Input and Output) unit
 6 into digital audio-signal data which is then supplied to an audio
 compression encoder/decoder 37.
 The digital audio-signal data is compressed by the audio compression
 encoder/decoder 37 in accordance with the ATRAC2 format mentioned earlier.
 The compressed audio-signal data is then written by the
 data-processing/system control circuit 31 into the buffer memory 32 at a
 predetermined data transfer rate to be stored therein temporarily.
 As described above, compressed video data and compressed audio-signal data
 are stored into the buffer memory 32. The buffer memory 32 mainly plays a
 role of absorbing a difference in data transfer rate between two data
 transfers, namely, the data transfer rate between the camera block 2 or
 the display/video/audio I/O unit 6 and the buffer memory 32 and the data
 transfer rate between the buffer memory 32 and the media drive unit 4.
 In a recording operation, the compressed video data and the compressed
 audio-signal data accumulated in the buffer memory 32 in the
 aforementioned manner are read out sequentially with predetermined timings
 and transferred to an MD-DATA2 encoder/decoder 41 employed in the media
 drive unit 4. It should be noted that, in a playback operation, for
 example, a sequence of recording operations ranging from the operation to
 read out data accumulated in the buffer memory 32 from the buffer memory
 32 to an operation to record the data read out from the buffer memory 32
 into the disc 51 mounted on the deck unit 5 by way of the media drive unit
 4 are inevitably carried out intermittently.
 Such operations to write data into and read out data from the buffer memory
 32 are controlled typically by the data-processing/system control circuit
 31.
 A playback operation carried out by the video-signal processing unit 3 is
 explained in a simple and plain manner as follows.
 In a playback operation, encoded compressed video data and compressed
 audio-signal data read out from the disc 51 are decoded by the MD-DATA2
 encoder/decoder 41 employed in the media drive unit 4 to generate decoded
 compressed video data and compressed audio-signal data which are then
 supplied to the data-processing/system control circuit 31.
 The data-processing/system control circuit 31 typically temporarily stores
 the compressed video data and the compressed audio-signal data supplied
 thereto in the buffer memory 32 temporarily. The compressed video data and
 compressed audio-signal data are then read out back from the buffer memory
 32 with appropriate timing and at a proper data transfer rate so as to
 obtain matching along the playback time axis. The compressed video data
 read out back from the buffer memory 32 is then supplied to the MPEG2
 video-signal processing circuit 33 whereas the compressed audio-signal
 data is fed to the audio compression encoder/decoder 37.
 The MPEG2 video-signal processing circuit 33 decompresses the compressed
 video data supplied thereto and transfers decompressed video data obtained
 as a result of the decompression to the data-processing/system control
 circuit 31. The data-processing/system control unit 31 supplies the
 decompressed video-signal data to a video D/A converter 61 employed in the
 display/video/audio I/O unit 6.
 In the audio compression encoder/decoder 37, on the other hand, the
 compressed audio-signal data transferred thereto is decompressed and then
 supplied to a D/A converter 65 employed in the display/video/audio I/O
 unit 6.
 In display/video/audio I/O unit 6, the video D/A converter 61 converts the
 video-signal data transferred thereto into an analog video-signal which is
 then split and supplied to a display controller 62 and a composite-signal
 processing circuit 63.
 The display controller 62 drives the display unit 6A in accordance with the
 video-signal supplied to the display controller 62. As a result, a
 playback picture appears on the display unit 6A. On the display unit 6A,
 not only can a picture played back from the disc 51 be displayed, but it
 is of course possible to output and display a picture obtained as a result
 of image shooting by a camera member comprising the lens block 1 and the
 camera block 2 in all but a real-time manner.
 In addition to a picture played back from the disc 51 and a picture
 obtained as a result of image shooting by the camera member, the display
 unit 6A is also capable of displaying a message expressed typically in
 terms of characters and figures to inform the user of necessary
 information on the operating state of the video camera as described
 earlier. An operation to display such a message is controlled by typically
 the video controller 38 so that required elements such as characters and
 figures composing the message are displayed at desired positions. To put
 it in detail, video-signal data of the required elements such as
 characters and figures composing the message is mixed with video-signal
 data to be output by the data-processing/system control circuit 31 to the
 video D/A converter 61 in such a way that the elements are displayed at
 the desired positions.
 The composite-signal processing circuit 63 converts the analog video-signal
 supplied thereto by the video D/A converter 61 into a composite signal
 output to a video output terminal T1. Typically, by connecting external
 equipment such as a monitor to the video output terminal T1, a picture
 played back by the video camera can be displayed on the external monitor.
 In the display/video/audio I/O unit 6, on the other hand, the audio-signal
 data supplied to the D/A converter 65 by the audio compression
 encoder/decoder 37 is converted by the D/A converter 65 into an analog
 audio-signal for outputting to a headphone/line terminal T2. The analog
 audio-signal output by the D/A converter 65 is split and output to the
 speaker SP by way of an amplifier 66. As a result, the speaker SP
 generates an output such as playback sound. It should be noted that, since
 the explanation of the A/D converter 64 is included in the description of
 the recording operation, it is not necessary to repeat the explanation
 here.
 Main functions of the media drive unit 4 are described as follows. In a
 recording operation, user data to be recorded with the MD-DATA2 format is
 encoded into code appropriate for disc recording and transferred to the
 deck unit 5. In a playback operation, on the other hand, data read out
 from the disc 51 mounted on the deck unit 5 is decoded to produce playback
 user data which is then transferred to the video-signal processing unit 3.
 In a recording operation, the MD-DATA2 encoder/decoder 41 employed in the
 media drive unit 4 receives recording data to be recorded from the
 data-processing/system control circuit 31 and carries out a predetermined
 encoding process on the recording data comprising compressed video data
 and compressed audio-signal data in accordance with the MD-DATA2 format.
 The encoded data is then stored in a buffer memory 42 temporarily to be
 read out later while being transferred to the deck unit 5 with proper
 timing.
 In a playback operation, on the other hand, the MD-DATA2 encoder/decoder 41
 inputs a digital playback signal read out from the disc 51 and supplied
 thereto by way of an RF-signal processing circuit 44 and a
 binary-conversion circuit 43, decoding the digital playback signal in
 accordance with the MD-DATA2 format. Playback user data obtained as a
 result of the decoding is transferred to the data-processing/system
 control circuit 31 employed in the video-signal processing unit 3.
 It should be noted that, also in a playback operation, the playback user
 data is once stored in the buffer memory 42, if necessary, to be read out
 back with proper timing and transferred to the data-processing/system
 control circuit 31. Operations to write and read out data into and from
 the buffer memory 42 are controlled by the driver controller 46.
 It is worth noting that, during an operation to play back data from the
 disc 51, the servo or other mechanisms may be out of control due to causes
 such as an external disturbance, making it no longer possible to read out
 a signal from the disc 51. Even in such a circumstance, however, the
 continuity of playback data along the time axis can be sustained provided
 that the operation to play back data from the disc 51 can be restored to a
 normal state as long as data to be read out is yet stored in the buffer
 memory 42.
 The RF-signal processing circuit 44 carries out necessary processing on a
 signal read out from the disc 51 to generate, for example, a playback data
 signal as an RF signal and a variety of servo-control signals for
 controlling the servo of the disc 51 such as a focus-error signal and a
 tracking-error signal. The RF signal is converted by the a
 binary-conversion circuit 43 into binary data which is then supplied to
 the MD-DATA2 encoder/decoder 41 as digital-signal data.
 The same variety of servo-control signals generated by the RF-signal
 processing circuit 44 are supplied to a servo circuit 45 for executing
 necessary servo control in the deck unit 5 based on the servo-control
 signals supplied thereto.
 It should be noted that the servo circuit 45 provided by the embodiment has
 a functional circuit that functions as an encoder/decoder for the MD-DATA1
 format. This functional circuit is capable of encoding user recording data
 supplied thereto from the video-signal processing unit 3 in accordance
 with the MD-DATA1 format and decoding data, which was encoded in the
 MD-DATAl format in advance, being read out from the disc 51 to be
 transferred to the video-signal processing unit 3. That is to say, the
 video camera implemented by the embodiment is designed to provide
 compatibility between the MD-DATA2 format and the MD-DATA1 format.
 A driver controller 46 serves as a functional circuit for totally
 controlling the media drive unit 4.
 The deck unit 5 is a member provided with a mechanism for driving the disc
 51. To be more specific, the deck unit 5 includes a mechanism, that is,
 the disc slot 203 of FIG. 4 which allows the disc 51 for the deck unit 5
 to be mounted onto and dismounted from the deck unit 5. Not shown in FIGS.
 5, 5A and 5B, the disc slot 203 thus allows the user to replace the
 mounted disc 51 with another one. The disc 51 is assumed to be an optical
 magnetic disc conforming to the MD-DATA1 or MD-DATA2 format.
 In the deck unit 5, the mounted disc 51 is driven into rotation by a
 spindle motor 52 at a CLV. During a recording or playback operation, an
 optical head 53 irradiates a laser beam to the disc 51.
 In a recording operation, the optical head 53 generates a laser output at a
 level high enough for heating the recording track on the disc 51 to a
 Curie temperature. In a playback operation, on the other hand, the optical
 head 53 generates a laser output at a relatively low level for detecting
 data from a light reflected by the disc 51 by a magnetic Kerr effect. Not
 explicitly shown in detail in FIGS. 5, 5A and 5B, the optical head 53 has
 components mounted thereon. The mounted components are an optical system
 comprising a laser diode, a polarization beam splitter and an objective
 lens, and a detector for detecting the reflected light. The objective lens
 mounted on the optical head 53 is held by a dual-axis mechanism in such a
 way that the objective lens can be displaced in the radial direction of
 the disc 51 and in a direction departing from or approaching the disc 51.
 A magnetic head 54 is installed on the other side of the disc 51 with
 respect to the optical head 53 at a counterpart position to the position
 of the optical head 53. The magnetic head 54 applies a magnetic field
 modulated by recording data to the disc 51.
 The deck unit 5 also has a sled mechanism driven by a sled motor 55. The
 sled mechanism itself is not shown in FIG. 5 though. By driving the sled
 mechanism, the entire optical head 53 and the optical head 54 can be moved
 in the radial direction of the disc 51.
 As explained earlier by referring to FIG. 4, the operation unit 7 is
 provided with a set of keys for use by the user to carry out a variety of
 operations.
 An external interface unit 8 allows data to be exchanged between this video
 camera with external equipment. The external interface unit 8 is typically
 provided between an I/F terminal T3 and the video-signal processing unit 3
 as shown in the figure. The external interface unit 8 is typically
 designed to conform to the IEEE1394 standard even though the external
 interface unit 8 is not necessarily limited to this standard.
 Assume, for example, that an external digital video apparatus is connected
 to the video camera implemented by the embodiment through the I/F terminal
 T3. In this case, a picture and/or audio picked up by the video camera can
 be recorded in the external digital video apparatus. In addition, a signal
 such as video and audio data played back by the external digital video
 apparatus can be supplied to the video camera by way of the external
 interface unit 8 to be recorded into the disc 51 in accordance with the
 MD-DATA2 or MD-DATA1 format.
 A power-supply block 9 supplies direct-current power generated by an
 embedded battery or generated from commercial alternating-current power to
 a variety of functional circuits at appropriate voltage levels.
 3. Configuration of the Media Drive Unit
 FIGS. 6, 6A and 6B are block diagrams showing a detailed configuration of
 MD-DATA2 functional circuits employed in the media drive unit 4 shown in
 FIGS. 5, 5A and 5B. It should be noted that, while FIGS. 6, 6A and 6B also
 show the deck unit 5 together with the media drive unit 4, the explanation
 of the internal configuration of the deck unit 5 is not repeated since its
 internal configuration has been explained earlier by referring to FIGS. 5,
 5A and 5B. In FIGS. 6A and 6B, components of the deck unit 5 are denoted
 by the same reference numerals used in FIGS. 5, 5A and 5B. By the same
 token, components of the media drive unit 4 shown in FIGS. 6, 6A and 6B
 identical with those shown in FIGS. 5, 5A and 5B are denoted by the same
 reference numerals as the latter.
 When the optical head 53 radiates light onto the disk 51, an optical
 current obtained by the photo detector employed in the optical head 53, as
 a result of detection of a reflected laser light, is supplied to the RF
 amplifier 101.
 The RF amplifier 101 generates a playback RF signal representing a playback
 signal from the detected information supplied thereto, then outputs the
 playback RF signal to the binary-conversion circuit 102, that is, the
 binary-conversion circuit 43 shown in FIGS. 5, 5A and 5B are The
 binary-conversion circuit 43 converts the playback RF signal into a binary
 RF signal or a digital playback RF signal.
 The binary RF signal is subjected to processes such as gain adjustment and
 clamp processing in an AGC/clamp circuit 103 before being supplied to an
 equalizer/PLL circuit 104.
 The equalizer/PLL circuit 104 carries out an equalizing process on the
 binary RF signal supplied thereto, then outputs the result to a Viterbi
 decoder 105. In addition, by supplying the binary RF signal completing the
 equalizing process to a PLL circuit, a clock signal CLK synchronized with
 the binary RF signal (a train of RLL (1, 7) codes) can be obtained.
 The frequency of the clock signal CLK represents the current rotational
 speed of the disc 51. Thus, a CLV processor 111 inputs the clock signal
 CLK from the equalizer/PLL circuit 104 and compares the frequency of the
 clock signal CLK with a reference value representing a predetermined CLV
 shown in the table of FIG. 3 to produce error information which is used as
 a signal component for generating a spindle-error signal SPE. In addition,
 the clock signal CLK is also used as a clock signal of processing carried
 out by a variety of signal-processing circuits such as an RLL (1, 7)
 demodulation circuit 106.
 The Viterbi decoder 105 decodes the binary RF signal supplied thereto from
 the equalizer/PLL circuit 104 by adopting a so-called Viterbi decoding
 method to produce a train codes of RLL (1, 7) (Run Length Limited)
 representing playback data.
 This playback data is supplied to the RLL (1, 7) demodulation circuit 106
 for carrying out RLL (1, 7) demodulation to generate a data stream.
 The data stream obtained as a result of the demodulation carried out by the
 RLL (1, 7) demodulation circuit 106 is written into the buffer memory 42
 through a data bus 114 to be laid out in the memory 42.
 The data stream laid out in the buffer memory 42 is subjected to error
 correction processing carried out by an ECC processing circuit 116 using
 an RS-PC technique in error correction block units before undergoing
 descramble processing and EDC-decode processing (Error Detected Code: a
 sort of error detection processing) in a descramble/EDC-decode circuit
 117. A result produced by the processing carried out so far is user
 playback data DATAP. The user playback data DATAp is, for example,
 transferred from the descramble/EDC-decode circuit 117 to the
 data-processing/system control circuit 31 employed in the video-signal
 processing unit 3 at a data transfer rate determined by a transfer clock
 signal generated by a transfer-clock generating circuit 121.
 The transfer-clock generating circuit 121 utilizes a clock of crystal
 system for generating a transfer clock signal at a frequency appropriate
 for, for example, data transfer between the media drive unit 4 and the
 video-signal processing unit 3 and among functional circuits within the
 media drive unit 4.
 Detected information, that is, an optical current, read out by the optical
 head 53 from the disc 51 is supplied to a matrix amplifier 107, too.
 The detected information supplied to the matrix amplifier 107 is subjected
 to necessary processing carried out by the matrix amplifier 107 to extract
 a tracking-error signal TE, a focus-error signal FE and groove information
 GFM, that is, an absolute address information recorded on the disc 51 as
 wobble of wobbled groove WG. The tracking-error signal TE and the
 focus-error signal FE are supplied to a servo processor 112 whereas the
 groove information GFM is supplied to an ADIP band-pass filter 108.
 After experiencing band filtering in the ADIP band-pass filter 108, the
 groove information GFM with band area restriction is supplied to an
 A/B-track detecting circuit 109, an ADIP decoder 110 and the CLV processor
 111.
 The A/B-track detecting circuit 109 forms a judgment as to whether the
 track currently being traced is track Tr A or Tr B. The judgment is formed
 by using typically the technique based on the groove information GFM
 supplied to the A/B-track detecting circuit 109 as explained earlier by
 referring to FIG. 2. The result of the judgment representing the track
 being traced currently is supplied to the driver controller 46. The ADIP
 decoder 110 decodes the groove information GFM supplied thereto to extract
 an ADIP signal representing information on an absolute address on the disc
 51. The ADIP signal is also supplied to the driver controller 46. The
 driver controller 46 executes necessary control based on the ADIP signal
 and the information indicating the track currently being used as described
 above.
 The CLV processor 111 receives the clock signal CLK from the equalizer/PLL
 circuit 104 and the groove information GFM from the ADIP band-pass filter
 108. The CLV processor 111 generates a spindle-error signal SPE for
 controlling the CLV servo from an error signal obtained typically as a
 result of integration of errors in phase between the groove information
 GFM and the clock signal CLK. The spindle-error signal SPE is supplied to
 the servo processor 112. It should be noted that necessary operations to
 be carried out by the CLV processor 111 are controlled by the driver
 controller 46.
 The servo processor 112 outputs a variety of servo control signals such as
 a tracking control signal, a focus control signal, a sled control signal
 and a spindle control signal based on the tracking-error signal TE, the
 focus-error signal FE and the spindle-error signal SPE supplied thereto as
 described above in addition to commands such as a track-jump command and
 an access command received from the driver controller 46 to a servo driver
 113.
 In turn, the servo driver 113 generates necessary servo drive signals based
 on the servo control signals supplied thereto by the servo processor 112.
 The servo drive signals are a dual-axis drive signal for driving the
 dual-axis mechanism in the focus direction, a dual-axis drive signal for
 driving the dual-axis mechanism in the tracking direction, a sled-motor
 drive signal for driving the sled mechanism and a spindle-motor drive
 signal for driving the spindle motor 52.
 These servo drive signals are supplied to the deck unit 5 to execute focus
 control and tracking control of the disc 51 as well as CLV control of the
 spindle motor 52.
 In an operation to record user recording data DATAr into the disc 51, for
 example, the DATAr is supplied to a scramble/EDC-encode circuit 115 by the
 data-processing/system control circuit 31 employed in the video-signal
 processing unit 3 in synchronization with typically the transfer clock
 signal generated by the transfer-clock generating circuit 121.
 In the scramble/EDC-encode circuit 115, the user recording data DATAr is
 written and laid out in the buffer memory 42 to undergo typically data
 scramble processing and EDC encode processing, that is, additional
 processing of error detection codes using a predetermined technique. After
 these pieces of processing, an ECC processing circuit 116 typically adds
 an error correction code based on the RS-PC technique to the user
 recording data DATAr laid out in the buffer memory 42.
 The user recording data DATAr completing the processing so far is read out
 back from the buffer memory 42 and supplied to an RLL (1, 7) modulation
 circuit 118 through a data bus 114.
 In the RLL (1, 7) modulation circuit 118, the user recording data DATAr
 supplied thereto is subjected to RLL (1, 7) modulation processing to
 generate a code trains of RLL (1, 7) which are output to a magnetic-head
 driving circuit 119 as recording data.
 In the case of the MD-DATA2 format, by the way, a so-called laser-strobe
 magnetic-field modulation system is adopted as a recording system for
 recording data on a disc. With the laser-strobe magnetic-field modulation
 system, a magnetic field modulated by data being recorded is applied to
 the recording surface of the disc and, at the same time, a laser light is
 irradiated to the disc as pulses synchronized with the recorded data. With
 laser-strobe magnetic-field modulation system, a process of forming a pit
 edge recorded on the disc is determined by irradiation timing of the laser
 pulses independently of a transient characteristic such as a reversing
 velocity of the magnetic field.
 As a result, with laser-strobe magnetic-field modulation system, the number
 of jitters of the recording pit can be reduced to an extremely small value
 with ease in comparison with, for example, a simple magnetic-field
 modulation system, a system whereby a laser light is irradiated to a disc
 in a steady state and, at the same time, a magnetic field modulated by
 data being recorded is applied to the recording surface of the disc. That
 is to say, the laser-strobe magnetic-field modulation system is a system
 advantageous to an effort to increase the recording density.
 The magnetic-head driving circuit 119 employed in the media drive unit 4
 drives the magnetic head 54 to apply a magnetic field modulated by data
 being recorded to disc 51. In addition, the RLL (1, 7) modulation circuit
 118 also outputs a clock signal synchronized with the data being recorded
 to the laser driver 120. On the basis of the clock signal, the laser
 driver 120 drives a laser diode employed in the optical head 53 so that
 laser pulses synchronized with data being recorded generated by the
 magnetic head 54 as the magnetic field are radiated to the disc 51. At
 that time, the laser pulses emitted by the laser diode have proper power
 required for recording. In this way, the media drive unit 4 is capable of
 carrying out an operation to record data into the disc 51 by adopting the
 laser-strobe magnetic-field modulation system described above.
 4. Operations in Stretched-Recording Mode
 4-1. Writing Data into a Buffer Memory
 Next, a typical recording mode characterizing the embodiment is exemplified
 by a recording operation carried out in a stretched-recording mode. First
 of all, an operation to write data into the buffer memory 32 is explained.
 FIG. 7 is a diagram showing conceptually a flow of data in an image
 shooting/recording operation carried out by the video camera implemented
 by the embodiment.
 Image shooting signal data or video data obtained as a result of image
 shooting by means of the camera unit, that is, the lens block 1 and the
 camera block 2, and audio-signal data of sound picked up by the microphone
 202 are compressed and then temporarily stored in the buffer-memory 32
 through write operations in accordance with the MPEG2 and ATRAC2 formats
 respectively as is obvious from the previous explanation with reference to
 FIGS. 5, 5A and 5B. Later, the compressed video data and the compressed
 audio-signal data are read out back from the buffer memory 32 and
 transferred to the drive unit comprising the media drive unit 4 and the
 deck unit 5 to be recorded onto the disc 51.
 As described above, the buffer memory 32 mainly plays a role of absorbing a
 difference in data transfer rate between 2 data transfers, namely, a data
 transfer between the camera unit comprising the lens block 1 and the
 camera block 2 or the mike unit, that is, the display/video/audio IO unit
 6, and the buffer memory 32 and a data transfer between the buffer memory
 32 and the drive unit comprising the media drive unit 4 and the deck unit
 5.
 Here, assume for example that an external disturbance such as vibration or
 a shock is given to the video camera implemented by the embodiment,
 putting the video camera in a circumstance in which an operation to record
 data onto the disc 51 can no longer be carried out in the drive unit. In
 such a circumstance, the rate of the data transfer from the buffer memory
 32 to the drive unit must be reduced and, as a result, the rate of the
 data transfer from the camera unit or the mike unit to the buffer memory
 32 is relatively high in comparison with the former data transfer. If the
 amount of information to be transferred from the camera unit or the mike
 unit to the buffer memory 32 becomes smaller for some reasons, on the
 other hand, the rate of the data transfer from the buffer memory 32 to the
 drive unit becomes relatively high in comparison with the rate of the data
 transfer from the camera unit or the mike unit to the buffer memory 32. As
 a result, the amount of data stored in the buffer memory 32 becomes
 smaller.
 Assuming a relation between data transfer speeds described above, think of
 an operation in a stretched-recording mode provided by the embodiment.
 A stretched recording operation takes place when the disc 51 is about to be
 replaced by a next one because the recording area in the disc 51 becomes
 all but full while the present video recording is being carried out. When
 the disc 51 is replaced by the next one, the present recording is
 suspended to be resumed later after the replacement is completed. While
 the disc 51 is being replaced with the next one, however, the image
 shooting is carried out as it is so that signal processing of video data
 and audio-signal data in the video-signal processing unit 3 can be
 continued. In the stretched recording operation, video data and
 audio-signal data obtained as a result of the signal processing which is
 carried out by the video-signal processing unit 3 while the disc 51 is
 being replaced with the next one are stored in the buffer memory 32. Then,
 by resuming the recording operation after the disc replacement has been
 completed, video data and audio data obtained during a period of time
 between the suspension of the data recording to replace the disc 51 and
 the resumption of the recording upon completion of the disc replacement
 can be prevented from being lost. Thus, data obtained in a
 stretched-recording operation is recorded into an area stretched over a
 plurality of discs wherein data recorded in a disc is followed by data
 recorded in a next disc continuously along the time axis with no
 information to be recorded lost.
 In the implementation of the stretched-recording operation discussed above,
 however, it is necessary to consider the size of a free area which is left
 in the buffer memory 32 at a point of time the video camera is put in a
 circumstance requiring the stretched recording due to the fact that the
 storage capacity of the buffer memory 32 is much limited.
 To put it in detail, the size of a free area left in the buffer memory 32,
 that is, the remaining capacity to store data, varies in dependence on the
 operating condition of the video camera at a point of time the video
 camera is put in a circumstance requiring the stretched recording. If the
 size of a free area left in the buffer memory 32 is large enough for
 assuring continuity of data along the time axis, that is, large enough for
 storing data output by the video-signal processing unit 3 during a period
 of time generally required to replace the disc 1, there will be no
 problem. If the size of a free area left in the buffer memory 32 is not
 large enough for storing data output by the video-signal processing unit 3
 during a period of time generally required to replace the disc 1, however,
 the buffer memory 32 will also become full, that is, the free area will be
 all used up, while the disc 1 is being replaced, in which case data can no
 longer be stored in the buffer memory 32. As a result, some information of
 data to be recorded into the disc 51 will be lost.
 In order to solve this problem, in a stretched-recording mode provided by
 the embodiment, signal processing and a recording operation described
 below are carried out so that as much continuity of data recorded in a
 storage area stretched over a plurality of discs along the time axis as
 possible is assured without regard to the size of the free area remaining
 in the buffer memory 32.
 FIG. 8A is a diagram conceptually showing compressed video data and
 compressed audio-signal data stored in the buffer memory unit 32. It
 should be noted that the buffer memory unit 32 is implemented in a system
 wherein it is assumed that the ratio of an area allocated to compressed
 video data to an area allocated to audio data can be changed arbitrarily.
 The following 2 equations hold true:
EQU Maudio=Taudio.times.Raudio (1)
EQU Mmovie=Tmovie.times.Rmovie (2)
 where
 notation Raudio is an audio data rate, that is, the rate of the transfer of
 audio data to the buffer memory unit 32;
 notation Taudio is an audio time duration, that is, the time duration to
 write audio data into the buffer memory unit 32;
 notation Maudio is an audio buffered amount, that is, the amount of audio
 data stored in the buffer memory unit 32;
 notation Rmovie is a moving-picture data rate, that is, the rate of the
 transfer of moving-picture data or, to be more specific, the rate of the
 transfer of video data compressed in accordance with the MPEG2 format, to
 the buffer memory unit 32;
 notation Tmovie is a moving-picture time duration, that is, the time
 duration to write video data into the buffer memory unit 32; and
 notation Mmovie is a moving-picture buffered amount, that is, the amount of
 video data stored in the buffer memory unit 32.
 FIG. 8A is a diagram showing quadrangles representing Eqs. (1) and (2). To
 be more specific, the length of the horizontal side and the length of the
 vertical side of the quadrangle on the right side represent the audio data
 rate Raudio and the audio time duration Taudio of Eq. (1) respectively.
 Thus, the area of the quadrangle represents the audio buffered amount
 Maudio. By the same token, the length of the horizontal side and the
 length of the vertical side of the quadrangle on the left side represent
 the moving-picture data rate Rmovie and the moving-picture time duration
 Tmovie of Eq. (2) respectively. Thus, the area of the quadrangle
 represents the moving-picture buffered amount Mmovie.
 Thus, the total buffered amount M, that is, the total amount of data stored
 in the buffer-memory area 32, is represented by the following equation:
EQU M=Maudio+Mmovie (3)
 That is to say, the total buffered amount M is the sum of the areas of the
 2 quadrangles shown in FIG. 8A.
 Typically, the moving-picture data rate Rmovie is about 4 Mbps (according
 to a full specification) and the audio data rate Raudio is about 0.1 Mbps.
 Thus, an area of the buffer memory unit 32 used for storing moving picture
 data is much larger than that used for storing audio data.
 For the above reason, when there is only a small free area left in the
 buffer memory area 32, audio data is stored in the buffer memory area 32,
 taking precedence of video data. On the basis of a rational described
 below, the moving-picture data rate Rmovie, that is the amount of
 moving-picture data stored in the buffer-memory unit 32 per unit time, is
 first of all reduced so that the amount of moving-picture data stored in
 the buffer-memory unit 32 per unit time decreases.
 The moving-picture data rate Rmovie is reduced typically by keeping the
 audio time duration Taudio equal to the moving-picture time duration
 Tmovie in the operation to write data into the buffer memory unit 32 as
 follows:
EQU Taudio=Tmovie (4)
 On the other hand, the amount of data stored during a period of time to
 replace the disc 1 is Tchange.times.(Rmovie+Raudio) where notation Tchange
 is the length of the period of time. In order to assure continuity of an
 operation to store compressed video data and compressed audio data into
 the buffer memory unit 32, the amount of data stored during a period of
 time to replace the disc 1 shall not exceed the total buffered amount M as
 indicated by the following relation.
EQU M&gt;Tchange.times.(Rmovie+Raudio) (5)
 Since the total buffered amount M can be interpreted as the size of the
 free area remaining in the buffer memory unit 32 and the period of time
 for disc replacement (Tchange) can be estimated, the sum (Rmovie+Raudio)
 can be found from Eq. (5). By continuing the operation to store compressed
 video data and compressed audio data at such a ratio, the free area left
 in the buffer memory unit 32 with a limited size can be utilized with the
 highest degree of efficiency.
 Given the rationale described above, the video camera is switched from the
 normal-recording mode to a mode of the stretched-recording mode of the
 embodiment in accordance with a detected size of a free area left in the
 buffer memory unit 32.
 To be more specific, at a point of time the size of the free area remaining
 in the disc 51 becomes equal to or smaller than a predetermined value, the
 video camera is switched from the normal-recording mode to the
 stretched-recording mode provided by the embodiment.
 In the stretched-recording mode, first of all, it is necessary to form a
 judgment as to whether or not the size Mrem of the free area remaining in
 the buffer memory unit 32 satisfies the following relation:
EQU Mrem&gt;Tchange.times.(Rmovie+Raudio) (6)
 wherein notation Rmovie is a maximum speed determined by a full
 specification. If relation (6) is satisfied, it is all but out of the
 bounds of possibility that the buffer memory unit 32 becomes full while
 the disc 1 is being replaced, breaking the continuity of data being
 recorded along the time axis. In this case, the video camera is kept in a
 normal mode of the stretched-recording mode.
 Diagrams of FIG. 8A correspond to the normal mode.
 As described above, the MPEG2 decompression/encoding system supports a VBR
 technique for varying the data rate at which moving-picture data is
 compressed and encoded. In the stretched-recording mode, the VBR system is
 implemented. In the normal mode, moving-picture data is compressed and
 encoded at a data rate corresponding to a maximum rate specified in a full
 specification, that is, the maximum value of the variable data rate of the
 VBR system. The compressed and encoded moving-picture data is then stored
 in the buffer memory unit 32 at the moving-picture data rate Rmovie
 corresponding to this data rate.
 On the other hand, audio data compressed in accordance with the ATRAC2
 format is stored in the buffer memory unit 32 at a fixed audio data rate
 Raudio in any modes to be described later.
 In the normal mode, data is stored into the buffer memory unit 32 typically
 in the same way as the normal-recording mode set prior to the
 stretched-recording mode. In the normal-recording mode, moving-picture
 data is stored in the buffer memory unit 32 typically at a data rate
 Rmovie corresponding to a maximum rate specified in a full specification,
 that is, the constant data rate of the CBR system.
 If relation (6) is not satisfied, on the other hand, the video camera is
 put in a variable-moving-picture-data-rate mode. In this mode, the
 moving-picture data rate Rmovie is reduced to a value Rmovie2 that
 satisfies relation (6). moving-picture data is thus stored in the buffer
 memory unit 32 at this reduced moving-picture data rate Rmovie2.
 A state of the buffer memory unit 32 in this
 variable-moving-picture-data-rate mode is shown in FIG. 8B.
 As shown in FIG. 8B, by storing moving-picture data in the buffer memory
 unit 32 at this reduced moving-picture data rate Rmovie2, the
 moving-picture buffered amount Mmovie, that is, the amount of
 moving-picture data stored in the buffer memory unit 32 per unit time is
 also reduced. Comparison of the state shown in FIG. 8A with that of FIG.
 8B indicates that, for the same total buffered amount M expressed by Eq.
 (3), the audio time duration Taudio and the moving-picture time duration
 Tmovie, that is, the lengths of the vertical sides of the quadrangles, are
 obviously longer in the variable-moving-picture-data-rate mode shown in
 FIG. 8B than those shown in FIG. 8A.
 It should be noted that, the lower the data rate of the moving-picture
 data, the poorer the quality of the picture image and the smaller the size
 of the picture image. At least, however, no information is missing
 completely from the flow of data recorded in a storage area stretched over
 2 discs along the time axis.
 In case relation (6) can not be satisfied even by a minimum moving-picture
 data rate Rmovie2 in the variable-rate range of the VBR system in the
 stretched-recording mode, the video camera is switched to a still-picture
 mode of the stretched-recording mode.
 In a still-picture mode, the MPEG2 video-signal processing circuit 33
 stores sequentially pieces of still-picture data Mpic obtained as a result
 of JPEG compression of video data extracted from moving-picture data
 supplied thereto with proper timing in frame or field units (or video data
 of I pictures obtained as a result of an MPEG2 encoding process) into the
 buffer memory unit 32.
 The amount of data stored in the buffer memory unit 32 corresponding to the
 moving-picture buffered amount Mmovie in the still-picture mode wherein
 pieces of still-picture data Mpic are sequentially stored in the buffer
 memory unit 32 is given by Eq. (7) as follows:
EQU Mmovie=Mpic.times.n (7)
 wherein notation Mmovie is the amount of data stored in the buffer memory
 unit 32 corresponding to the moving-picture buffered amount Mmovie in the
 still-picture mode, notation Mpic is the amount of still-picture data and
 the symbol n is the number of still pictures. In this case, the audio
 buffered amount Maudio is expressed by Eq. (8) as follows:
EQU Maudio=Tchange.times.Raudio (8)
 Since audio-sign al data is stored in the buffer memory unit 32, taking
 precedence of still-picture data, the still-picture data is stored in the
 remaining free area of the buffer memory unit 32 with a size equal to
 (Mrem-Maudio). Thus, the number of still pictures (n) is given by Eq. (9)
 as follows:
EQU n=(Mrem-maudio)/Mpic (9)
 Timing with which still-picture data are extracted from moving-picture
 data, that is, a time interval (Tstil) at which still-picture data are
 extracted from moving-picture data, is typically set in accordance with
 Eq. (10) as follows:
EQU Tstil=Tchange/n (10)
 By setting the timing as described above, as many still pictures as the
 free area in the buffer memory unit 32 is capable of accommodating can be
 obtained at all but equal time intervals.
 FIG. 8C is a diagram showing a typical operation carried out in the
 still-picture mode. As compressed video data to be stored in the buffer
 memory unit 32, moving-picture data is not written into the buffer memory
 unit 32. Instead, still pictures Mpic (i), - - - , Mpic (n-1) and Mpic (n)
 are written thereto in accordance with the rules described above. The
 amount of the stored still pictures Mpic (i), - - - , Mpic (n-1) and Mpic
 (n) corresponding to the moving-picture buffered amount Mmovie given by
 Eq. (7) becomes very small. It is thus obvious that the time duration
 Taudio of audio data becomes very long by an increase commensurate with
 the reduction in Mmovie in comparison with Taudio shown in FIG. 8B. In the
 still-picture mode, however, recorded and reproduced video data is
 intermittent instead of being continuous along the time axis. As for audio
 data, continuity along the time axis can be assured.
 In addition, even if still pictures are written in a still-picture mode,
 when the size Mrem of a free area remaining in the buffer memory unit 32
 after transition to the stretched-recording mode can not assure the audio
 buffered amount Maudio expressed by Eq. (8), an audio mode of the
 stretched-recording mode not shown in the figure is set.
 In the audio mode, an operation to store even still-picture data in the
 buffer memory unit 32 as compressed video data is halted. That is to say,
 only audio data is stored in the memory unit 32.
 In this case, a disc replacement time Tchange expressed by the following
 equation can be assured.
EQU Tchange=Taudio=Mrem/Raudio
 While no video information is recorded during the disc replacement time
 Tchange, continuity of audio data along the time axis can be assured.
 It should be noted that, in the case of an audio compression system with a
 variable data rate, for example, in the audio mode, the compressibility is
 increased as the size Mrem of a free area remaining in the buffer memory
 unit 32 decreases. Thus, it is quite within the bounds of possibility that
 audio data must be written into the buffer memory unit 32 at an audio data
 rate Raudio lower than a full-specification value.
 Assume that one of the normal mode, the variable-moving-picture-data-rate
 mode, the still-picture mode and the audio mode is selected in accordance
 with the size Mrem of a free area remaining in the buffer memory unit 32
 upon transition to the stretched-recording mode as described above. In
 this case, by storing data to be recorded into the buffer memory unit 32
 in the selected mode, the size Mrem of a free area remaining in the buffer
 memory unit 32 assures that data of a period of t i m e corresponding to
 the disc replacement time Tchange c a n be stored in the free area. Then,
 during the stretched-recording mode, first of all, video recording is
 continued till the current disc 51 used for video recording so far becomes
 full. As the current disc 51 becomes full, the user replaces the current
 disc 51 with a replacement one during a sufficient period of time within
 the estimated disc replacement time Tchange and then resumes the video
 recording. It should be noted that, after the user replaces the current
 disc 51 with a replacement one and then resumes the video recording, the
 video camera is switched from the stretched-recording mode to the
 normal-recording mode. In the normal-recording mode, data is stored in the
 buffer memory unit 32 in the same recording operation as the normal mode
 explained earlier by referring to FIG. 8A. By virtue of the
 stretched-recording mode, continuity of video and audio along the time
 axis from the disc 51 prior to the replacement to a replacement disc is
 assured if one of the conditions for the normal mode, the
 variable-moving-picture-data-rate mode and the still-picture mode is
 satisfied. At least, continuity of the recorded audio data along the time
 axis is assured even if the worst comes to the worst, that is, if only the
 condition for the audio mode is satisfied.
 4-2 Recording of Additional Information
 The following is a description of additional information associated with a
 plurality of discs involved in a recording operation carried out in a
 stretched-recording mode to record data of video recording in an area
 stretched over the same plurality of discs. Additional information is a
 sort of control information such as information on a link between 2 discs
 and an identification of each individual disc other than video data and
 audio data recorded as user data described above.
 FIG. 10 is a diagram showing a typical structure of an area stretched from
 an innermost circumference of the disc 51 provided by the embodiment to an
 outermost thereof.
 On an optical magnetic disc used as the disc 51, the area on the innermost
 circumference is used as a pit area in which data dedicated for a playback
 operation by an emboss pit is created. In this pit area, a P-TOC
 (premastered TOC) is recorded. An area on the outer side of the pit area
 is an optical magnetic area, that is, an area which data can be recorded
 into and played back from. The optical magnetic area comprises lands Ld
 serving as recording tracks Tr.cndot.A and Tr.cndot.B, wobbled grooves WG
 and non-wobbled grooves NWG described earlier by referring to FIGS. 1 and
 2.
 A segment with a predetermined size on the innermost circumference of the
 optical magnetic area is used as a control area. The rest on outer
 circumferences of the optical magnetic area is a program area used for
 recording an actual program such as a musical piece. Mainly recorded in
 the control area is necessary control information which is required for
 controlling operations to record and playback a file into and from
 typically a U-TOC (user-TOC) disc. In this embodiment, the additional
 information is written into a predetermined region of this control area in
 accordance with a predetermined structure. An area on the
 outer-circumference side of the program area is used as a lead-out area.
 In this embodiment, the additional information to be written onto the above
 control area typically includes pieces of data 1 to 7 described as
 follows:
 1. A continuous-recording disc number: A sequence number assigned to each
 of a plurality of discs involved in video recording in a
 stretched-recording mode for recording data continuously along the time
 axis in an area stretched over the same plurality of discs. The sequence
 numbers indicate the order of discs in which data is recorded on the
 discs. When data is recorded on first to Nth discs, for example,
 continuous-recording disc numbers #1, #2, #3, - - - , #N are assigned to
 the first, second, third, - - - , Nth discs respectively.
 2. Succeeding-disc link number: A number assigned to each of a plurality of
 discs and used as a link to a next disc involved in video recording in a
 stretched-recording mode for recording data continuously along the time
 axis in an area stretched over the same plurality of discs. A
 succeeding-disc link number is typically represented by a unique number
 based on a time and a date at which the disc is replaced.
 3. Preceding-disc link number: A number assigned to each of a plurality of
 discs and used as a link to a preceding disc involved in video recording
 in a stretched-recording mode for recording data continuously along the
 time axis in an area stretched over the same plurality of discs. A
 preceding-disc link number is the counterpart of a succeeding-disc link
 number described above.
 4. Preceding-disc ID: The name of a preceding disc of a plurality of discs
 linked to this disc involved in video recording in a stretched-recording
 mode for recording data continuously along the time axis in an area
 stretched over the same plurality of discs. A unique ID is assigned to
 each of the discs. In the case of the second disc, for example, the
 preceding-disc ID is the unique ID assigned to the first disc. In the case
 of the third or subsequent disc, the preceding-disc ID is the unique ID
 assigned to the second disc or a subsequent disc and so on. It should be
 noted that a unique ID assigned to each disc is recorded in the control
 area of the disc without regard to whether or not video recording of data
 in a stretched-recording mode is carried out.
 5. Stretched-recording mode attribute information: Includes information
 indicating the normal mode, the variable-moving-picture-data-rate mode,
 the still-picture mode or the audio mode selected as a mode of the
 stretched-recording mode and information showing an area for recording in
 the stretched-recording mode. If the variable-moving-picture-data-rate
 mode is selected, for example, the stretched-recording mode attribute
 information also includes a data rate set in the
 variable-moving-picture-data-rate mode. If the still-picture mode is
 selected, the stretched-recording mode attribute information includes the
 number of still pictures to be recorded.
 6. Disc name: A name automatically assigned to each of a plurality of discs
 involved in recording in a stretched-recording mode for recording data
 continuously along the time axis in an area stretched over the same
 plurality of discs. A disc name is an identification of a disc that can be
 displayed with ease typically in terms of characters. For example,
 possible disc names assigned to the first, second and third discs and so
 on are respectively "****", "****2", and "****3" et cetera. A disc name
 can be read out from the disc and displayed on the display unit 6A.
 7. File name: A name automatically assigned to each file containing
 collected data in a plurality of discs involved in recording in a
 stretched-recording mode for recording data continuously along the time
 axis in an area stretched over the same plurality of discs. In the case of
 2 discs involved in recording in a stretched-recording mode for recording
 data continuously along the time axis in an area stretched over the 2
 discs, for example, it is necessary to treat the data recorded in the area
 stretched over the 2 discs as a file.
 There are a variety of possible ways for assigning a file name. Typically,
 a file name conforms to the disc name described above. If the name
 assigned to a file recorded on the first disc is "*-*-", for example,
 names "*-*-2", "*-*-3" and so on are assigned to the same file on the
 consecutive second and third discs et cetera respectively. A file name can
 be read out from the disc and displayed on the display unit 6A.
 Typically, the pieces of additional information 1 to 7 are written into the
 control area of the disc 51 on predetermined occasions during processing
 described below. By recording additional information in the
 stretched-recording mode on the disc 51, the information can be reproduced
 when necessary typically in a playback operation to be output to the
 display unit 6A. As a result, a library of a plurality of discs involved
 in stretched recording can be controlled with ease.
 It should be noted that the additional information described above is no
 more than examples to the bitter end. That is to say, other kinds of
 additional information are conceivable. In addition, it is also possible
 to utilize only some of the additional information depending on how discs
 are controlled.
 5. Processing Operations
 The following is a description of processing operations for implementing
 the stretched-recording mode explained so far with reference to a
 flowchart shown in FIGS. 9, 9A and 9B. It should be noted that processing
 represented by the flowchart shown in this figure is mainly carried out by
 the video controller 38 in conjunction with the driver controller 46.
 The processing represented by the flowchart shown in this figure is started
 from a state of a recording operation carried out in the normal-recording
 mode.
 As shown by the flowchart of this figure, the processing begins with a step
 S101 at which the size of a free recording area remaining in the current
 disc 51 for recording video data and audio data is detected to form a
 judgment as to whether the detected size has become equal to or smaller
 than a predetermined value used as a criterion to switch from the
 normal-recording mode to the stretched-recording mode. The judgment can be
 based on an address at which the recording operation is currently being
 carried out by the driver controller 46 or the size of an area already
 used so far for recording.
 If the outcome of the judgment formed at the step S101 indicates that the
 size of a free recording area remaining in the current disc 51 has become
 equal to or smaller than a predetermined value, the flow of the processing
 goes on to a step S102 at which the video controller 38 switches the
 recording mode to the stretched-recording mode. The flow of the processing
 then proceeds to a step S103 at which the size Mrem of a free area
 remaining in the buffer memory unit 32 is evaluated as the first
 processing in the stretched-recording mode to form a judgment as to
 whether the size Mrem of a free area remaining in the buffer memory unit
 32 is within a predetermined range Mrem1, Mrem2, Mrem3 or Mrem4.
 The range Mrem4 is a range of Mrem sizes of a free area remaining in the
 buffer memory unit 32 that allows data to be recorded in the normal mode
 explained earlier by referring to FIG. 8A. The range Mrem3 is a range of
 Mrem sizes of a free area remaining in the buffer memory unit 32 that
 allows data to be recorded in the variable-moving-picture-data-rate mode.
 The range Mrem2 is a range of Mrem sizes of a free area remaining in the
 buffer memory unit 32 that allows data to be recorded in the still-picture
 mode. The range Mrem1 is a range of Mrem sizes of a free area remaining in
 the buffer memory unit 32 that allows data to be recorded in the audio
 mode. The predetermined ranges Mrem1, Mrem2, Mrem3 and Mrem4 thus satisfy
 the following relation:
EQU 0.ltoreq.Mrem1&lt;Mrem2&lt;Mrem3&lt;Mrem4.ltoreq.M
 where the symbol M is the size of the whole buffer memory unit 32.
 If the evaluation of the step S103 indicates that the size Mrem of a free
 area remaining in the buffer memory unit 32 is in the range Mrem4, the
 flow of the processing goes on to a step S104 at which the video
 controller 38 carries out processing to write data into the buffer memory
 unit 32 in the normal mode. The processing carried out at the step S104
 has been explained earlier by referring to FIG. 8A.
 If the evaluation of the step S103 indicates that the size Mrem of a free
 area remaining in the buffer memory unit 32 is in the range Mrem3, the
 flow of the processing goes on to a step S105 at which the
 variable-moving-picture-data-rate mode is set. The flow of the processing
 then proceeds to a step S106 at which data of a moving-picture is stored
 into the buffer memory unit 32 at a moving-picture data rate Rmovie
 determined by controlling the MPEG2 video-signal processing circuit 33 at
 a value appropriate for the size of Mrem in the range Mrem 3.
 If the evaluation of the step S103 indicates that the size Mrem of a free
 area remaining in the buffer memory unit 32 is in the range Mrem2, the
 flow of the processing goes on to a step S107 at which the still-picture
 mode is set. The flow of the processing then proceeds to a step S108 at
 which data of a number of still pictures is stored into the buffer memory
 unit 32. The number of still pictures is set by controlling the MPEG2
 video-signal processing circuit 33 at a value appropriate for the size of
 Mrem in the range Mrem2. The still pictures output by the MPEG2
 video-signal processing circuit 33 are stored in the buffer memory unit 32
 with proper timing along with audio data.
 If the evaluation of the step S103 indicates that the size Mrem of a free
 area remaining in the buffer memory unit 32 is in the range Mrem1, the
 flow of the processing goes on to a step S109 at which the audio mode is
 set. The flow of the processing then proceeds to a step S110 at which only
 audio data is stored in the buffer memory unit 32. That is to say,
 compressed video data is not stored in buffer memory unit 32.
 Then, the flow of the processing continues from the steps S104, S106, S108
 or S110 to a step S111 to form a judgment as to whether or not the size of
 a recording area remaining in the disc 51 has become 0. That is to say,
 the step Sill is a state of waiting for the recording area of the disc 51
 to become full, allowing no more data to be recorded therein. As the
 recording area of the disc 51 becomes full, the flow of the processing
 goes on to a step S112.
 At the step S112, additional information required by the disc 51 used for
 the recording carried out so far is generated and recorded in the control
 area of the disc 51. Some or all of the pieces of additional information 1
 to 7 which are required for the disc 51 are recorded. Typically, the
 processing of the step S112 is carried out by the driver controller 46
 employed in the media drive unit 4.
 As the processing carried out at the step S112 is finished, the flow of the
 processing proceeds to a step S113 at which the video controller 38
 typically executes control to display a message urging the user to replace
 the disc 51 on the display unit 6A or to output an audio signal advising
 the user to do so. The output message or the audio signal makes the user
 aware of the fact that the end of the recording time or the end of the
 remaining recording area is imminent. As a result, the time to replace the
 disc 51 can not be overlooked. At that time, the video controller 38 is
 capable of computing the allowable maximum length of the disc replacement
 time Tchange, that is, a period of time between the start of the disc
 replacement and a point of time the buffer memory unit 32 is all filled up
 by data written thereto in the stretched-recording mode. In order to
 improve the video camera more operatable in a way desired by the user, it
 is desirable to also display Tchange, that is, a period of time provided
 to the user for replacing the disc 51 before the buffer memory unit 32
 becomes full.
 After the processing carried out at the step S113 is finished, the flow
 continues to a step S114 to form a judgment as to whether or not the
 manual work done by the user to replace the disc 51 has been completed.
 Typically, the deck unit 5 is provided with a mechanical switch or a photo
 detector which is capable of detecting a state with a disc 51 mounted and
 a state with a disc 51 removed and distinguishing the states from each
 other. The judgment is formed by the driver controller 46 on the basis of
 a detection signal generated by the mechanical switch or the photo
 detector to indicate that a disc 51 has been newly mounted. As the outcome
 of the judgment formed at the step S114 indicates that the manual work
 done by the user to replace the disc 51 has been completed, the flow of
 the processing goes on to a step S115 at which the driver controller 46
 typically records additional information into the control area of the
 replacement disc 51.
 The flow of the processing then goes on to a step S116 at which the
 stretched-recording mode is ended and the normal-recording mode is
 reestablished to resume the operation to record moving-picture data and
 audio data this time on the replacement disc 51. In this case, the rate of
 the moving-picture data is the full-specification maximum value.
 In a normal recording operation, a shock or an external disturbance may be
 given to the main body of the video camera sometimes, making it impossible
 to record data on the disc 51. Even in such a circumstance, the size Mrem
 of a free area remaining in the buffer memory unit 32 keeps decreasing. If
 such a circumstance continues, the size Mrem of a free area remaining in
 the buffer memory unit 32 becomes insufficient.
 Thus, there is a case other than the disc replacement described above in
 which it is quite within the bounds of possibility that continuity of
 video recording of data onto the disc 51 along the time axis can not be
 assured any more. In order to solve this problem, the ranges Mrem1, Mrem2,
 Mrem3 and Mrem4 are determined by considering, among other factors, an
 assumed time it takes to recover the operation to record data on the disc
 51. Execution of the pieces of processing of the steps S103 to S110 of the
 flowchart shown in FIG. 9 based on the ranges Mrem1, Mrem2, Mrem3 and
 Mrem4 is of course conceivable. In this case, however, the driver
 controller 46 is put in a state of waiting for the operation to record
 data on the disc 51 to be recovered while data is being written into the
 buffer memory unit 32 in the normal mode, the
 variable-moving-picture-data-rate mode, the still-picture mode or the
 audio mode. As the operation to record data on the disc 51 is recovered,
 the normal recording mode is resumed with proper timing.
 6. Playback Operation
 The following is a brief description of an operation to play back data
 recorded on the disc 51 in the stretched-recording mode explained earlier.
 In a playback operation, first of all, information is read out from the
 control area of a disc 51 mounted on the deck unit 5 of the video camera.
 At that time, pieces of additional information 1 to 7 related to the
 stretched-recording mode described earlier are also read out as well. The
 additional information read out from the control area of the disc 51 is
 stored in a predetermined area of the buffer memory unit 42. of course,
 the driver controller 46 appropriately utilizes the additional information
 stored in the buffer memory unit 42 for necessary control of the media
 drive unit 4 and also transfers the additional information to the video
 controller 38. The video controller 38 is thus capable of executing
 necessary control of the video-signal processing unit 3 by using the
 additional information.
 In an operation to play back data recorded in the stretched-recording mode
 as part of the operation to play back data from the disc 51, the video
 controller 38 typically executes necessary control of a variety of
 functional circuits employed in the video-signal processing unit 3 based
 on the additional information so as to set a playback mode corresponding
 to the normal mode, the variable-moving-picture-data-rate mode, the
 still-picture mode or the audio mode selected as a mode of the stretched
 recording mode to write data in the buffer memory unit 32. Particularly,
 in an operation to play back data recorded in the
 variable-moving-picture-data-rate mode, the video controller 38 typically
 executes control of the same variety of functional circuits such as mainly
 the MPEG2 video-signal processing circuit 33 so as to carry out necessary
 signal processing, mainly decoding appropriate for a data rate of
 moving-picture data set in the variable-moving-picture-data-rate mode.
 In addition, in an operation to play back data recorded in the
 still-picture mode, the video-signal processing unit 3 decompresses
 still-picture data played back from the disc 51 in accordance with
 typically a JPEG format or the format of the MPEG2 I picture. The video
 controller 38 controls the video-signal processing unit 3 so that still
 pictures are sequentially output and displayed with timing corresponding
 to the timing used in the still-picture mode. Typically, the still
 pictures are output and displayed at intervals expressed by Eq. (10).
 In addition, in an operation to play back data recorded in the audio mode,
 only audio data read out from the disc 51 is played back and output as an
 audio-signal. It should be noted that, at that time, a blue-back technique
 is typically applied to display a picture as a possible operation. The
 blue-back technique sustains a state to display last video data among
 recorded data obtained prior to the audio mode on a still-picture screen.
 Assume that, in an operation to play back data recorded on the disc 51 in
 the stretched-recording mode, a disc following this recording 51 is
 required to undergo the so-called stretched playback operation. In this
 case, the video controller 38 executes control so that a message based on
 the additional information is typically generated and output to the
 display unit 6A or an external monitor unit to make the user able to
 recognize the following disc which remains to be played back. By taking a
 look at the message, the user is capable of recognizing the following disc
 containing continuation data of the disc 51 currently being played back.
 Thus, the user can make a preparation for the next playback operation in
 advance.
 It should be noted that implementations of the present invention are not
 limited to the embodiment. That is to say, the scope of the present
 invention includes a variety of modifications of the embodiment. For
 example, in the video camera implemented by the embodiment, a disc
 recording/reproducing apparatus based on the MD-DATA2 format is employed
 as a video recording/playback member. Considering the object of the
 present invention to prevent continuity of video-recording data along the
 time axis from becoming unsustainable in a stretched-recording operation,
 however, a recording/reproducing apparatus for recording media of types
 other than the disc each with a configuration different from that provided
 by the embodiment can also be employed as a video recording/playback
 member. An example of such other recording media is a tape.
 In addition, the MPEG2 system in the embodiment is typically adopted as a
 technique for compressing data of a video as described above. It is worth
 noting, however, that the compression method is not limited to the MPEG2
 system in particular. Any video compressing system can be embraced as long
 as the system supports a variable data rate of video data subjected to the
 compression and encoding process. Furthermore, the technique to compress
 data of still pictures and audio data do not have to be respectively the
 JPEG and ATRAC2 methods adopted in the embodiment in particular.
 As described above, under a condition that it is quite within the bounds of
 possibility that continuity of data being recorded on a disc during a
 normal recording operation along the time axis is unsustainable, the
 recording apparatus provided by the embodiment measures the size of a free
 area remaining in a storage means for temporarily storing compressed video
 data and compressed audio data. The recording apparatus then switches the
 normal-recording operation to one of stretched-recording operations with
 compressed audio data given a priority higher than that of compressed
 video data. The stretched-recording operation selected in dependence on
 the size of the free area is an operation with a reduced rate of
 compressed video data being written into the storage means, an operation
 to write compressed data of still pictures in place of video into the
 storage means or an operation to write only compressed audio data into the
 storage means, excluding video data. In a worst condition, continuity of
 compressed audio data being recorded on a disc can be sustained. If such a
 recording apparatus is employed in a video camera, for example, continuity
 of data recorded in an area stretched over a plurality of discs along the
 time axis can be obtained, allowing the video camera to be operated more
 in a way desired by the user.