Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Reexamination Certificate
2000-05-30
2002-01-08
Tran, Thai (Department: 2615)
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
C386S349000, C386S349000
Reexamination Certificate
active
06337948
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital signal record apparatus which is useful in a digital video tape recorder (hereinafter, referred to as “a digital VTR”), a digital disk player, or the like having a track format that records digital video and audio signals in respective predetermined areas in a slant track, and which receives digital video and audio signals in the form of a bitstream and records the bitstream, and also to a digital signal playback apparatus which plays back a record medium on which recording was conducted by the digital signal record apparatus.
2. Description of Related Art
FIG. 1
is a diagram showing a track pattern employed in a common home digital VTR of the prior art. As shown, slant tracks are formed on a magnetic tape, and each track is divided into two areas, a video area for recording a digital video signal and an audio area for recording a digital audio signal.
There are two methods to record video and audio signals on such home digital VTRs. One is the so-called baseband recording method in which the video and audio signals are inputted in analog form, and recorded in digital form after performing a high-efficiency coding to reduce data rate; the other is the so-called transparent recording method in which bitstreams transmitted in digital form are recorded.
For recording of the Advanced Television (ATV) signal currently under consideration in the United States, or the Digital Video Broadcasting (DVB) signal currently under investigation in Europe, the latter method, i.e., the transparent recording method, is suitable. Major reasons are that the ATV signal or the DVB signal is already digital-compressed and does not require high-efficiency encoders or decoders, and that there occurs no degradation in picture quality since the signal is recorded directly. On the other hand, the major drawback is inferior picture quality in trick playback modes such as high-speed playback, still-motion playback, and slow motion playback. In particular, by simply recording bitstreams directly on slant tracks, useful pictures cannot be reproduced in high-speed playback.
One digital VTR method for recording the ATV signal was proposed in a technical report “A Recording Method of ATV data on a Consumer Digital VCR” presented at “International Workshop on HDTV '93” held from October 26 to 28 in Ottawa, Canada. This report will be used as the prior art in the following description.
According to the basic specification of a prototype home digital VTR, assuming the recording rate of the digital video signal is 25 Mbps and the field frequency is 60 Hz, one video frame is recorded in video areas on 10 tracks in standard definition (SD) mode. Here, if the data rate of the ATV signal is 17 to 18 Mbps. transparent recording of the ATV signal is possible in this SD mode.
FIGS. 2A and 2B
are diagrams showing head scan paths in normal playback and high-speed playback on a digital VTR. As shown, adjacent slant tracks are recorded alternately across the tape by rotary heads having different azimuth angles. In normal playback, the tape transport speed is the same as in recording, so that the rotary heads precisely trace the recorded tracks as shown in FIG.
2
A. In high-speed playback, on the other hand, since the tape speed is different, the heads move across several tracks, each head thus being able to play back only fragments of the same azimuth tracks.
FIG. 2B
shows an example in fast forward playback at the speed five times the normal speed.
In MPEG2 bitstreams (bitstreams of the ATV signal and the DVB signal are substantially compatible with MPEG2 bitstreams), only intracoded blocks can be decoded independently without referencing other frames. If an MPEG2 bitstream is recorded on tracks in successive order, in high-speed playback, intra-coded data is taken out of a playback signal by intermittent playback and an image is reconstructed only by the intra-coded data. In this case, on the screen the reproduced areas will be non-continuous, and fragments of blocks will be dispersed across the screen. Furthermore, since the bitstream is variable-length encoded, there is no guarantee that the whole screen will be updated periodically, and there is a possibility that some portions may remain undated for long periods of time. As a result, the picture quality in high-speed playback will not be sufficient and unacceptable for a home digital VTR.
FIG. 3
is a block diagram showing a bitstream recording apparatus of the prior art capable of performing a high-speed playback. Here, the video area on each track is divided into a main area, where the whole bitstream of the ATV signal is recorded, and a duplication area, where portions of the bitstream critical for image reconstruction in high-speed playback are recorded (such portions are hereinafter referred to as High Priority (HP) data). Since only intra-coded blocks are valid in high-speed playback, intra-coded blocks are recorded in the duplication area; to further reduce the data amount, low-frequency components are extracted from all the intra-coded blocks and recorded as HP data. In
FIG. 3
, reference numeral
301
is a bitstream input terminal,
302
is a bitstream output terminal,
303
is an HP data output terminal,
304
is a variable-length decoder,
305
is a counter,
306
is a data extraction circuit, and
307
is an EOB (end of block) appending circuit.
An MPEG2 bitstream is inputted via the input terminal
301
and outputted unprocessed via the output terminal
302
for recording successively in the main area. The bitstream inputted via the input terminal
301
is also fed to the variable-length decoder
304
, which analyzes the syntax of the MPEG2 bitstream and detects an intra-image; in response, the counter
305
generates the timing at which the data extraction circuit
306
extracts the low-frequency components of each block of the intra-image. Then, the EOB appending circuit
307
appends an EOB to construct HP data which is recorded in the duplication area.
FIG. 4
is a diagram conceptually showing normal playback and high-speed playback in a prior art digital VTR. In normal playback, the whole bitstream recorded in the main area is reproduced and supplied to an MPEG2 decoder external to the digital VTR. The HP data is discarded. On the other hand, in high-speed playback, only the HP data recorded in the duplication area is selected and sent to the decoder, while the bitstream from the main area is discarded.
Next, the arrangement of the main area and duplication area on each track will be described.
FIG. 5
is a diagram showing an example of the scan path of the rotary head in common high-speed playback. If the tape speed is an integral multiple of the normal speed and phase-lock controlled, the head scanning is synchronized with the tracks with the same azimuth, reproducing data always from the same positions. In
FIG. 5
, if portions of the reproduced signal whose output levels are higher than −6 dB are played back, hatched regions will be played back by one head.
FIG. 5
shows an example of high-speed playback 9 times the normal speed. At this 9-times playback speed, it is guaranteed that the signal will be read from the hatched regions. It can therefore be seen that the HP data should be recorded in these areas. However, at other fast playback speeds, there is no guarantee that the signal will be read; the regions need to be set so that the signal can be read at different tape speeds.
FIG. 6
is a diagram showing overlapped areas in plural types of conventional high-speed playback, and it shows examples of scan areas of three types of tape speed in which the rotary head is synchronized with the same azimuth track. Some of the regions scanned at various tape speeds overlap. Duplication areas are selected from among these regions to guarantee HP data reading at different tape speeds. Shown in
FIG. 6
are examples of fast playback 4, 9, and 17 times the normal speed. The scan areas shown are the same as those that will be selected for fast
Inoue Sadayuki
Onishi Ken
Shinohara Junko
Yamasaki Tatsuo
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