Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Reexamination Certificate
1999-06-15
2003-07-15
Tran, Thai (Department: 2615)
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
C386S349000
Reexamination Certificate
active
06594442
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a recording medium to and from which digital data may be written and read, to a recording unit recording digital data on it, and to a playback unit playing back digital data from it. Particularly, the present invention relates to an optical disk on which multimedia data, such as video data, still image data, and audio data, may be recorded and to a recording unit and playback unit.
A phase-change disk DVD-RAM (Digital Versatile Disc-RAM) with a capacity of several GB (Giga Bytes) has been introduced into the field of writable optical disks with a maximum capacity of about 650 MB (Mega Bytes). As MPEG (MPEG2), the standard for coding digital AV (Audio and Video) data, is employed for practical use, DVD-RAM is now expected for use not only on computers but also as recording and playback media in the AV field. That is, it is predicted that DVD-RAMs will become media replacing magnetic tapes which have been used as standard AV recording media.
(Description of DVD-RAM) Recently, as the recording density of a rewritable optical disk increases, not only computer data or audio data but also image data may be recorded on the optical disk. For example, on the signal-recording surface of an optical disk, the guide grooves in the form of projection and ditch have been provided conventionally.
In former days, signals were recorded only in the projection or the ditch positions. The introduction of the land-groove recording method has made it possible for signals be recorded in both the projection and the ditch positions. This method has achieved about twice as high density as before (For example, Japanese Patent Laid-Open Application No. JP-A-8-7282).
The CLV method (Constant Line Velocity) efficiently increases the recording density. A method such as the zone CLV method which makes the CLV method easier to control and implement was also devised and put into practical use (For example, Japanese Patent Laid-Open Application No. JP-A-7-93873).
One of major problems with an optical disk with an ever-increasing capacity is how to record AV data, including image data, and how to implement performance and new functions much higher than those of conventional AV equipment.
With the advent of this large-capacity, rewritable optical disk, it is expected that tapes which have been used in most cases for AV data recording and playback will be replaced by optical disks. A shift in recording media from tapes to disks will have various influences on the function and performance of AV equipment.
One of the most prominent advantages of the shift to disks is a great improvement in the random access performance. An attempt to make a random access to data on a tape involves rewinding one volume of tape which will usually take the order of minutes. This is much larger than the seek time (several ten milli-second or less) of optical disk media. Thus, the tape cannot be used practically as a random access device.
This random access performance of an optical disk makes possible the distributed recording of AV data which would be impossible on conventional tapes.
FIG. 1
is a block diagram showing the drive of a DVD recorder. In the figure, reference numeral
11
is an optical pickup which reads data from the disk,
12
is an ECC (error correcting code) processor,
13
is a track buffer,
14
is a switch switching input/output of the track buffer,
15
is an encoder,
16
is a decoder, and
17
is the enlarged view of a recording area on the disk.
As shown in
17
, the minimum unit of data recorded on the DVD-RAM disk is 1 sector=2 KB. The ECC processor
12
performs error correction processing on 16 sectors=1 ECC block.
The track buffer shown by
13
is a buffer used to record AV data at variable bit rates to efficiently record AV data on the DVD-RAM disk. This buffer acts as a buffer to resolve the difference between the DVD-RAM read/write rate (Va in the figure) which is constant the and the AV data bit rate (Vb in the figure) which varies according to the complexity of the contents (such as image data of video).
More efficient use of this track buffer
13
allows AV data to be distributed on the disk. This is described below using
FIGS. 2A and 2B
.
FIG. 2A
is a diagram showing the address space of the disk. As shown in
FIG. 2A
, when AV data is recorded in separate contiguous areas [a
1
, a
2
] and [a
3
, a
4
], supplying data, stored in the track buffer, to the decoder during the seek operation from a
2
to a
3
allows AV data to be played back continuously.
FIG. 2B
shows how data is accumulated into, and supplied from, the track buffer.
AV data, which is read starting from a
1
, is input into, and output to, the track buffer beginning at time t
1
. The amount of data corresponding to the difference in rate (Va−Vb) between the track buffer input rate (Va) and the track buffer output rate (Vb) is accumulated in the track buffer. This condition continues until data at a
2
is read (time t
2
). The amount of data B(t
2
), accumulated up to this time, is used as data that is supplied to the decoder until time t
3
at which reading starts at a
3
arrives.
In other words, if the amount of data ([a
1
, a
2
]) accumulated before the seek operation is equal to or larger than a sufficient amount, AV data may be supplied continuously even if the seek operation happens.
In the above example, data is read, or played back, from a DVD-RAM. The example also applies when data is written, or recorded, onto the DVD-RAM.
As described above, if the data exceeding a sufficient amount is contiguously recorded on the DVD-RAM, continuous playback/recording is possible even if AV data is distributed on the disk.
(Description of MPEG)
Next, AV data is described.
As described above, AV data recorded on a DVD-RAM uses the international standard called MPEG (ISO/IEC13818).
A DVD-RAM, with a large capacity of several GB, is not large enough to store non-compressed digital AV data. This means that AV data must be compressed before being recorded. One of the popular methods for compressing AV data is MPEG (ISO/IEC13818). A recent advance in the LSI technology makes it possible to implement an MPEG codec (compression/decompression LSI chip), allowing the DVD recorder to MPEG-compress/decompress data.
For highly efficient data compression, MPEG has the following two major characteristics:
The first characteristic is that, in addition to the conventional compression method using the spatial frequency characteristics, MPEG uses a compression method using inter-frame time correlation characteristics for compressing video data. To compress data, MPEG classifies frames (also called pictures in MPEG) into three: I picture (intra-frame coded picture), P picture (picture using intra-frame coding and a reference to the preceding picture), and B picture (picture using intra-frame coding and a reference to the preceding and following pictures).
FIG. 3
shows the relation among I, P, and B pictures. As shown in
FIG. 3
, the P picture refers to the immediately preceding I or P picture, while the B picture refers to the immediately preceding and following I or P picture. Also, because the B picture refers to the following I or P picture, the display order of pictures does not always match that (coding order) of compressed data as shown in FIG.
3
.
The second characteristic is that MPEG allocates an amount of coding dynamically to each picture depending upon the complexity of the image. The MPEG decoder has an input buffer and accumulates data in this decoder buffer, making it possible to allocate a large amount of code to a complex image which is difficult to compress.
Audio data used on a DVD-RAM may be selected from the following three: MPEG audio data and Dolby digital data (AC-3) which are compressed and LPCM data which is not compressed. The bit rate of Dolby digital data and LPCM data is fixed. The size of MPEG audio data may be selected from several sizes in units of audio frames which are not so large as video streams.
This AV data i
Date Akira
Ito Tamotsu
Kageyama Masahiro
Murase Kaoru
Okada Tomoyuki
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Tran Thai
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