Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1999-09-28
2002-07-02
Kelley, Chris (Department: 2713)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240160
Reexamination Certificate
active
06414993
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a decoder for a compressed data stream and, more particularly, to a decoder for concurrently decoding plural compressed data streams, which have been coded through an inter-frame predictive encoding such as MPEG (Motion Picture Experts Group) standards.
DESCRIPTION OF THE RELATED ART
Firstly, description is made on a prior art decoder for a single data stream.
FIG. 1
illustrates a prior art video decoder. Reference numeral
101
designates an optical disk. A video signal and an audio signal arc compressed and coded in accordance with the MPEG standards, and bit strings are recorded in the optical disk
101
. The optical disk
101
is associated with a read-out circuit
102
, and the read-out circuit
102
reads out the bit strings from the optical disk
101
as a single data stream. The single data stream is deinterleaved or separated, and error bits are corrected. Finally, the read-out circuit
102
transfers bit strings
121
to a memory
103
for storing the bit strings
121
therein. A read-out control circuit (not shown) supplies an address signal to the memory
103
, and the bit strings
121
are read out from the memory
103
in a different order.
The memory
103
is connected to a decoder
108
, and the bit strings
121
are supplied to the decoder
108
. The bit strings
121
are decoded. The decoder
108
outputs a reproducing signal
181
for reproducing a picture on a display (not shown). The decoder
108
is connected to frame memories
191
/
192
/
193
, and the frame memories
191
/
192
/
193
stores pieces of video data information representative of reference pictures, i.e., I-picture and P-picture and other pieces of video data information representative of B-picture.
Subsequently, description is made on the predictive method for the MPEG system.
FIG. 2
illustrates a GOP (Group Of Picture). Plural frames
0
,
1
,
2
,
3
,
4
,
5
,
6
, . . . successively appear, and each frame contains pieces of video data information representative of a picture. The frame number is increased with time. The frame
6
is next to the frame
5
, and the pictures are successively reproduced in the order of frame number. “I”, “B” and “P” are selectively assigned to the frames
0
,
1
,
2
,
3
,
4
,
5
,
6
. . . , and indicate kinds of pictures. The picture labeled with “P” is referred to as “P-picture”, and the picture labeled with “I” and the picture labeled with “B” are referred to as “I-picture” and “B-picture”, respectively. The I-picture is coded by using pieces of data information only in the frame. P-picture or I-picture is to be called as a core picture. The P-picture is a kind of unidirectional predictive coded picture, and is coded by using an I-picture or a P-picture three frames before it as a reference picture. For example, the P-picture in the frame
6
is unidirectionally coded through the predictive encoding technique by using the P-picture in the frame
3
as the reference picture. The B-picture features the MPEG system. The B-picture is a kind of bidirectional predictive coded picture, and is coded by using the pictures in both sides thereof as the reference picture. For example, the B-picture is the frame
5
is bidirectionally coded through the predictive encoding technique by using the P-pictures in the frames
3
and
6
.
When the pictures in the frames
0
to
6
are coded, bit strings I
0
, P
3
, B
1
, B
2
, P
6
, B
4
and B
5
are arranged as shown in FIG.
3
. The reference I
0
means the bit string representative of the I-picture in the frame
0
, and the reference P
3
means the bit string representative of the P-picture in the frame
3
. The reference B
1
means the bit string representative of the B-picture in the frame
1
. Thus, the bit strings I
0
-B
5
are arranged differently from the frames
0
to
6
in order to effectively decode the bit strings.
Turning back to
FIG. 1
, the prior art video image decoder reproduces the pictures as follows. The read-out circuit
102
reads out pieces of data information from the optical disk
101
, and supplies the bit strings
121
to the memory
103
. The bit strings
121
follow the order of frames
0
,
1
,
2
,
3
,
4
,
5
,
6
, . . . , i.e., I
0
, B
1
, B
2
, P
3
, B
4
, B
5
, P
6
, . . . The bit strings
121
are written into the memory
103
, and are rearranged into the order shown in
FIG. 3
in the memory
103
.
Subsequently, the bit strings
121
are sequentially read out from the memory
103
. The bit strings are arranged as I
0
, P
3
, B
1
, B
2
, P
6
, B
4
, B
5
, . . . as shown in FIG.
3
. The bit strings I
0
, P
3
, B
1
, B
2
, P
6
, B
4
, B
5
, . . . are successively supplied to the decoder
108
, and are decoded as the reproducing signal
181
. While the decoder
108
is decoding the bit strings, the bit strings I
0
, P
3
, B
1
, B
2
, P
6
, B
4
, B
5
, . . . are processed as follows. Firstly, the bit string I
0
is decoded, and the decoded signal DI
0
is stored in the frame memory
191
. The decoded signal DI
0
is output as the reproducing signal
181
. The decoder
108
refers to the decoded signal DI
0
representative of the I-picture stored in the frame memory
191
, and the bit string P
3
is decoded to decoded signal DP
3
. The decoded signal DP
3
is stored in the frame memory
192
, and is output as the reproducing signal
181
. Subsequently, the decoder
108
refers to the decoded signals DI
0
and DP
3
stored in the frame memories
191
/
192
, and the bit string B
1
is decoded to a decoded signal DB
1
. The decoded signal DB
1
is stored in the frame memory
193
, and forms a part of the reproducing signal
181
. The decoder
108
also refers to the decoded signals DI
0
and DP
3
stored in the frame memories
191
/
192
, and the bit string B
2
is decoded to a decoded signal DB
2
. The decoded signal DB
2
is stored in the frame memory
193
, and forms a part of the reproducing signal
181
. The decoder
108
refers to the decoded signal DP
3
stored in the frame memory
192
, and the bit string P
6
is decoded to a decoded signal DP
6
. The decoded signal DP
6
is stored in the frame memory
191
, because the decoded signal DP
0
has been already unnecessary.
The prior art video decoder effectively reproduces the reproducing signal
181
from the single data stream read out from the optical disk
101
. However, the circuit arrangement of the prior art video decoder is less pertinent to the reproduction of pictures from plural data streams.
FIG. 4
illustrates three pictures reproduced on a display
195
. The picture on the left side of the display
195
is reproduced from a compressed data stream A, and the pictures on the right side are reproduced from compressed data streams B and C, respectively. The MPEG decoder is used for the compressed data streams A, B and C, and the compressed data streams contain bit strings representative of B-pictures.
The three pictures are concurrently reproduced on the display
195
through the decoding shown in FIG.
5
. Time passes from the left side to the right side.
FIG. 5
shows “FIELD”, “BIT STRING TO BE DECODED”, “PICTURE ON DISPLAY”, “WRITE-IN FRAME MEMORY” and “READ-OUT FRAME MEMORY” for the compressed data stream A. “WRITE-IN FRAME MEMORY” and “READ-OUT FRAME MEMORY” mean the frame memory in which a decoded signal is to be written and the frame memory from which a decoded signal is to be read out, respectively. A picture stored in a frame is reproduced on a display through two scannings. Frame “1” and frame “2” are indicative of the first scanning and the second scanning, respectively, and are corresponding to “top” of the picture to be displayed and “bottom” of the picture to be displayed, respectively. Although the second row “BIT STRINGS TO BE DECODED” indicates the bit strings of the compressed data stream A, the bit strings of the compressed data stream B and the bit strings of the compressed data stream C are also decoded in two third of each frame in a time sharing fashion. Similarly, the third row “PICTURE ON DISPLAY” indicates the pictures reproduced from the com
Kelley Chris
Scully Scott Murphy & Presser
Vo Tung T
LandOfFree
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