Television – Bandwidth reduction system – Data rate reduction
Reexamination Certificate
1998-06-19
2003-01-07
Rao, Andy (Department: 2613)
Television
Bandwidth reduction system
Data rate reduction
C375S240270
Reexamination Certificate
active
06504576
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital signal coding method and apparatus, a signal recording medium, and a signal transmission method and in particular, to a digital signal coding method and apparatus, a signal recording medium, and a signal transmission method which can preferably be applied for a case of recording a moving picture signal and an acoustic signal on a recording medium such as a magneto-optical disc and a magnetic tape and reproducing the signals to be displayed on a display or for a video conference system or a broadcast apparatus for transmitting a moving picture signal and an acoustic signal from a transmission side to a reception side via a transmission path, so that the signals are received and displayed at the reception side.
2. Description of the Prior Art
A digital signal obtained by digitizing a moving picture signal, an acoustic signal, or the like has a plenty of information amount. Consequently, when recording the digital signal on a recording medium having a small storage information amount for a long period of time, or when transmitting the digital signal through a limited communication path with a plenty of channels, it is indispensable to provide means for coding the digital signal with a high efficiency. In order to answer such a requirement, there have been suggested high-efficiency coding methods using a correlation of a video signal. One of the methods is the MPEG method or MPEG specification. The MPEG (Moving Picture Image Coding Experts Group) was discussed and proposed as a standard plan in the ISO-IEC/HTC1/SC2/WG11. The MPEG specification is a hybrid method using a motion compensative predictive coding and a discrete cosine transform (DCT) in combination. In this MPEG method, firstly a video signal difference between frames is determined so as to remove a redundancy in the time axis direction and the discrete cosine transform is used to remove a redundancy in the spatial axis direction, thus enabling to encode a video signal with a high efficiency.
The MPEG specification consists of three parts: the MPEG video (ISO/IEC11172-2 or ISO/IEC13818-2) for a high-efficiency coding of a video signal; the MPEG audio (ISO/IEC11172-3 or ISO.IEC13818-3) for a high-efficiency coding of an audio signal; and the MPEG system (ISO/IEC11172-1 or ISO/IEC13818-1) for multiplexing compressed video and audio bit streams into a single bit stream and reproducing the stream with synchronization.
FIG. 1
is a block diagram showing a configuration example of a digital signal coding apparatus of a conventional MPEG method. Here, a feed forward control is carried out for determining an assignment (target) bit amount for each of input pictures when coding an input video signal. That is, a video signal S
101
inputted from a terminal
200
is supplied to a frame memory
201
. The frame memory
201
is capable of storing a predetermined length of an input video signal. Here, the predetermined time length is, for example, 0.5 seconds (15 frames in the case of NTSC). An image coding controller
202
reads a video signal S
111
from the frame memory
201
and, for coding each of the pictures, calculates an assignment bit amount S
112
and a picture coding parameter S
117
. More specifically, an assignment bit amount for a predetermined time length of a video signal is optimally distributed according to the images of the respective pictures. A video encoder
203
encodes a picture S
102
supplied from the frame memory
201
according to the coding parameter S
117
, so that the picture S
102
has the assignment bit amount S
112
supplied from the image coding controller
202
, and outputs a coded bit stream S
103
of the picture S
102
and a generated coding bit amount S
113
. The coded bit stream S
103
is supplied to a buffer
204
and to an access unit detector
201
. Moreover, the generated coding bit amount S
113
outputted from the video encoder
203
is supplied to the image coding controller
202
. In the image coding controller
202
, if the generated bit amount is greater than the assignment bit amount, control is made so as to make the next assignment bit amount smaller; and if the generated bit amount is smaller than the assignment bit amount, control is made so as to make the next assignment bit amount greater.
An audio signal S
105
inputted from a terminal
205
is supplied to an audio encoder
206
. The audio encoder
206
encodes the input audio signal S
105
on audio frame basis by way of the MPEG audio method and outputs a coded bit stream S
106
to a buffer
207
and to the access unit detector
211
. Here, one audio frame consists of
1152
samples in the case of the MPEG audio layer
2
.
A sub picture signal S
108
such as a superimpose information inputted from a terminal
208
is supplied to a sub picture encoder
209
. The sub picture encoder
209
encodes each sub picture by way of the Run Length method, for example, and outputs a coded bit stream S
109
obtained to a buffer
210
and to the access unit detector
211
.
The access unit detector
211
detects a coding bit amount, a decoding time information, and a display time information of an access unit (decoding unit) of the video, audio, and sub picture coded bit streams and outputs the obtained information as an access unit information S
114
. Here, the access unit is one picture of a video signal, one frame of an audio signal, and one picture of a sub picture signal.
The video bit stream, the audio bit stream, and the sub picture bit stream are time-division multiplexed by the MPEG system method. The bit streams which have been multiplexed by the MPEG system method is formatted, for example, as shown in FIG.
2
. In this
FIG. 2
, V. A, S respectively represent a video bit stream packet, an audio bit stream packet, and a sub picture bit stream packet. A packet has a configuration having a header information consisting of a decoding time information, display time information, and the like which is followed by a coded bit stream.
A multiplex scheduler
212
, according to the access unit information S
114
, determines a schedule information S
115
for time-division multiplexing the video, the audio, and the sub picture coded bit streams.
That is, the MPEG system method defines a system target decoder (STD) which is a virtual decoder model as shown in
FIG. 3
, and the multiplexed bit stream should be encoded while maintaining this system target decoder. This system target decoder (STD) shown in
FIG. 3
will be detailed below.
In
FIG. 3
, a multiplexed bit stream is inputted from a terminal
301
, and a switch
302
, from this stream, isolates a video bit stream packet, an audio bit stream packet, and a sub picture bit stream packet, which packets are respectively supplied to a buffer
303
, a buffer
305
, and a buffer
307
. A video decoder
304
, an audio decoder
306
, and a sub picture decoder
308
read out an access unit from respective buffers according to the decoding time information of the access unit of the coded bit streams stored in the respective buffers, and decode the access unit, so as to reproduce with synchronization the video , the audio, and the sub picture according to the display time information of the access unit. Here, the multiplexed bit stream should be coded so as to maintain the system target decoder, preventing overflow and underflow of the buffer
303
, the buffer
305
, and the buffer
307
. The buffer overflow means that a bit stream storage amount exceeds a buffer capacity; and the buffer underflow means that an access unit is not entirely stored in the buffer by the decoding time of the access unit.
FIG. 4
shows a transition of a bit occupation in the STD buffer. In this
FIG. 4
, B represents a size of the STD buffer, and the vertical axis represents the buffer bit occupation amount or a data amount. A data input to the STD buffer is carried out with an input rate indicated by the inclination of the straight line ascending rightward, which increases the bit occupation amount. Moreover, in this figure
Frommer William S.
Frommer & Lawrence & Haug LLP
Rao Andy
Sony Corporation
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