Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Reexamination Certificate
2000-05-17
2002-01-15
Tran, Thai (Department: 2615)
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
C386S349000, C386S349000, C386S349000
Reexamination Certificate
active
06339670
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a digital video tape recorder (hereinafter referred to as digital VTR) having a track format for recording digital video and audio signals in predetermined areas on oblique tracks, and relates to a digital VTR in which the digital video and audio signals are input in the form of a bit stream, and the bit stream is magnetically recorded and played back.
FIG. 93
is a diagram showing a track pattern of a conventional, general consumer digital VTR. Referring to the drawing, a plurality of tracks are formed on a magnetic tape
10
, in a head scanning direction inclined to the tape transport direction, and digital video and audio signals are recorded therein. Each track is divided into two areas, a video area
12
for recording a digital video signal and an audio area
14
for recording a digital audio signal.
Two methods are available for recording video and audio signals on a video tape for such a consumer digital VTR. In one of the methods, analog video and audio signals are input, and recorded, using a video and audio high-efficiency encoding means; this is called a baseband recording method. In the other method, the bit stream having been digitally transmitted; this method is called a transparent recording method.
For the system of recording ATV (advanced television) signals, now under consideration in the United States, the latter transparent recording method is suitable. This is because the ATV signal is digitally compressed signals, and does not require a high-efficiency encoding means or a decoding means, and because there is not degradation in the picture quality due to transmission.
The transparent recording system however is associated with a picture quality problem in a special playback mode, such as a fast playback mode, a still mode and a slow mode. In particular, when a rotary head scans the tape obliquely to record a bit stream, almost no image is played back at the time of fast playback, if no specific measure is taken.
An improvement for the picture quality for the transparent recording system recording the ATV signal is described in an article Yanagihara, et al, “A Recording Method of ATV data on a Consumer Digital VCR”, in International Workshop on HDTV, 93, Oct. 26 to 28, 1993, Ottawa, Canada, Proceedings, Vol. II. This proposal is now explained.
In one basic specification of a prototype consumer digital VTR, in SD (standard definition) mode, when the recording rate of the digital video signal is 25 Mbps, and the field frequency is 60 Hz, two rotary heads are used for recording a digital video signal of one frame, being divided into video areas on 10 tracks. If the data rate of the ATV signal is 17 to 18 Mbps, transparent recording of the ATV signal is possible with the recording rate in this SD mode.
FIG.
94
A and
FIG. 94B
show tracks formed in a magnetic tape using a conventional digital VTR.
FIG. 94A
is a diagram showing scanning traces of the rotary heads during normal playback.
FIG. 94B
shows scanning traces of the rotary heads during fast playback. In the example under consideration, the rotary heads are opposite each other spaced 180° apart on a rotary drum, and the magnetic tape is wrapped around over 180°. In the drawing, adjacent tracks on the tape
10
are scanned by two rotary heads A and B having different azimuth angles, alternately and obliquely, to record digital data. In normal playback, the transport speed of the tape
10
is identical to that during recording, so that the heads trace along the recorded tracks. During fast playback, the tape speed is different, so that the heads A and B trace the magnetic tape
10
crossing several tracks. The arrow in
FIG. 94B
indicates a scanning trace by head A at the time of five-time fast feeding. The width of arrow represents the width of the region read by the head. Fractions of digital data recorded on tracks having an identical azimuth angle are played back from regions meshed in the drawings, within five tracks on the magnetic tape
10
.
The bit stream of the ATV signal is according to the MPEG2 standard. In this bit stream according to the MPEG2 standard, only the intra-frame or intra-field encoded data of the video signal, i.e., the data of intra encoded block (intra encoded block) alone can be decoded independently, without reference to data of another frame or field. Where the bit stream is recorded in turn on the respective tracks, the recorded data are replayed intermittently from the tracks during fast replay, and the image must be reconstructed from only the intra-encoded blocks contained in the replay data. Accordingly, the video area updated on the screen is not continuous, and only the fractions of data of intra coded block are replayed, and may be scattered over the screen. The bit stream is variable-length encoded, so that it is not ensured that all the replay data over the screen is periodically updated, and the replay data of certain parts of the video area may not be updated for a long time. As a result, this type of bit stream recording system does not provide a sufficient picture quality during fast replay in order to be accepted as a recording method for a consumer digital VTR.
FIG. 95
is a block configuration diagram showing an example of recording system in a conventional digital VTR. Referring to the drawing, reference numeral
16
denotes an input terminal for the bit stream,
18
denotes an output terminal for the bit stream,
20
denotes an HP data format circuit,
22
denotes a variable-length decoder,
24
denotes a counter,
26
denotes data extractor, and
28
denotes an EOB (end of block) appending circuit.
To improve the quality of fast replay pictures, the video area on each track is divided into two types of areas. That is, the video area on each track is divided into main areas
30
for recording the bit stream of the ATV signal, and copy areas for recording important part of the bit stream which are used for reconstruction of the image in fast replay. Only the intra-encoded blocks are effective during fast replay, so that they are recorded in the copy areas. To reduce the data further, only the low-frequency components are extracted from all the intra-encoded blocks, and recorded as HP (high priority) data.
The bit stream of MPEG2 is input via the input terminal
16
, and output via the output terminal
18
, without modification, and sequentially recorded in the main areas
30
on each track of the tape. The bit stream from the input terminal
16
is also input to the variable-length decoder
22
, and the syntax of the bit stream of the MPEG2 is analyzed, and the intra-picture data is detected, and timing signals are generated by the counter
24
, and the low-frequency components of all the blocks in the intra-picture data are extracted at the data extractor
26
. Furthermore, EOBs are appended at the EOB appending circuit
28
, and HP data is constructed at an HP data format circuit, not shown. The HP data is incorporated in the recording data for one track, and recorded in the copy areas
32
.
FIG.
96
A and
FIG. 96B
show an example of replay system in a conventional digital VTR.
FIG. 96A
schematically shows normal replay.
FIG. 96B
schematically shows fast replay.
Separation of data from the magnetic tape during normal replay and fast replay are performed respectively in the following ways. During normal replay, all the bit stream recorded in the main areas
30
is replayed, and the bit stream from the data separation means
34
is sent as the normal replay data, to an MPEG2 decoder, provided outside the replay system. The HP data from the copy areas
32
are discarded. During fast replay, only the HP data from the copy areas
32
are collected, and sent, as fast replay data, to the decoder. At the data separation means
34
, the bit stream from the main areas
30
is discarded.
A method of fast replay from a track in which main areas
30
and copy areas
32
is next described.
FIG. 97A
shows a scanning trace of a head.
FIG. 97B
shows track regions from which the replay is possible.
Asamura Masako
Hibi Taketoshi
Inoue Sadayuki
Inoue Tohru
Ishimoto Junko
Mitsubishi Denki & Kabushiki Kaisha
Tran Thai
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