Multiplex communications – Pathfinding or routing – Through a circuit switch
Reexamination Certificate
1998-12-09
2002-07-09
Chin, Wellington (Department: 2664)
Multiplex communications
Pathfinding or routing
Through a circuit switch
C348S423100
Reexamination Certificate
active
06418140
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of data multiplexing utilized in multiplexing digital data including pictures, audio and characters, and transmitting or recording the resultant multiplex data, a method of decoding the multiplexed data, a decoder using the decoding method, a multiplexed data repeater disposed between a multiplexer and the decoder, and a recording medium in which the methods are recorded.
PRIOR ART
An international standard called “MPEG 2” is a method of multiplexing digital data such as pictures, audio and characters. (Reference Documents: ISO/IEC JTC1/SC29/WG11 N801, “ISO/IEC 13818-1 International Standard: Information Technology—Generic Coding of Moving Pictures and Associated Audio Information: Systems”, 1994. 11)
FIG. 13
is a block diagram of a multiplexing system that multiplexes pictures and audio data coded in the MPEG 2 format. The multiplexing system surrounded by a broken line comprises a picture data buffer
1305
, a audio data buffer
1306
, a packetizer
1307
, a padding packet buffer
1309
, a multiplexer
1311
, and a timing generator
1314
. A picture encoder
1301
and an audio encoder
1303
are coupled to this multiplexing system.
FIG. 14
is a flowchart depicting an operation of a selector
1311
.
FIG. 15
is a schematic diagram illustrating a data structure of MPEG 2.
FIG. 16
illustrates a method of multiplexing data in MPEG 2 format. A conventional multiplexing method in MPEG 2 format is described hereinafter with reference to
FIGS. 13
,
14
,
15
and
16
.
FIG. 15
is a schematic diagram illustrating a data structure of MPEG 2. A picture or an audio data shown in FIG.
15
(
a
) is cut out in a given size, then a header is attached to the taken-out picture or audio data as shown in FIG.
15
(
b
) before being packetized into a PES packet. As shown in FIG.
15
(
c
), the header includes an identifier for identifying a kind of data, a decoding time at which a frame of picture or an audio data should be decoded as well as a reproduction time at which the frame of the picture or the audio data should be reproduced. One picture frame comprises one picture, and an audio frame comprises e.g. 1152 audio samples. Further, as shown in FIG.
15
(
d
) and FIG.
15
(
e
), another header called a pack header is included in the packet. The pack header includes a sample value of a reference time that is used for reproducing the reference time that is produced in the decoder.
An operation of the multiplexing system shown in
FIG. 13
is described hereinafter. The picture encoder
1301
encodes (compression) one picture frame and outputs a picture data
1302
. An audio encoder
1303
encodes one frame of audio data and outputs an audio data
1304
. The picture data and the audio data supplied to the multiplexing system are stored in the respective buffers
1305
and
1306
. The timing generator
1314
generates a timing with which a packet should be supplied, and inputs the packet generating signal into the multiplexer
1311
. The multiplexer operates following the flowchart shown in FIG.
14
. When the packet generating signal
1315
is supplied in step
1401
, a packet is selected for outputting process. In this process, it is assumed that a decoder is employed in the later process, and the packet is selected so that the buffer in the assumed decoder for pictures or audio data could avoid being overflowed or underflowed. A buffer capacity for pictures or audio data is standardized by MPEG 2, e.g. 1.8 M bit for pictures, 4096 bytes for audio data.
First, in step
1402
, when a vacant capacity for one packet is found in the audio data buffer of the assumed decoder, an audio-packet-generating-signal
1313
is supplied to the packetizer
1307
in step
1403
. The packetizer receives audio data for one packet from the buffer
1305
, and outputs an audio packet
1308
. When a vacant capacity for one packet is not found in the audio data buffer, while it is found in the picture data buffer of the assumed decoder in step
1404
, a picture packet generating signal
1313
is supplied to the packetizer in step
1405
. The packetizer receives a packet data for one packet from the buffer
1306
and outputs a picture packet
1308
. In step
1407
, when the multiplexer receives an audio packet or a picture packet, a reference time is attached to the received packet. When neither the audio data buffer nor picture data buffer has a vacant capacity for one packet, a padding packet
1310
is supplied to the multiplexer from a padding packet buffer
1309
in step
1406
. In step
1408
, the multiplexer outputs a received packet
1312
.
FIG. 16
illustrates transitional occupied capacities of the picture data and audio data buffers, which are used in the multiplexer
1311
shown in the flowchart of FIG.
14
. FIG.
16
(
b
) depicts the transitional occupied capacity of audio data buffer. The X-axis indicates time “t” that is a reference time reproduced from the reference time sample value shown in
FIG. 15. A
data for one audio frame is decoded at the time of “ta1”, “ta2”, . . . respectively, and they are deleted from the buffer. The time, “ta1”, “ta2”, . . . , are the decoding time included in the packet header shown in FIG.
15
(
c
). The Y-axis indicates a packet capacity occupied by data, and a broken line indicates a buffer size “Sa”. FIG.
16
(
c
) depicts the transitional occupied capacity of picture data buffer. A data for one picture frame is decoded at the time of “tv1”, “tv2”, . . . respectively, and they are deleted from the buffer. The Y-axis indicates a packet capacity occupied by data, and a broken line indicates a buffer size “Sv”. FIG.
16
(
a
) depicts a packet stream
1312
that is tapped off from the selector
1311
. Until the time “ta1”, a vacant capacity for one packet is not available in the audio data buffer, while it is available in the picture data buffer. A picture packet is thus multiplexed. Because an audio frame is decoded at “ta1”, an audio packet is multiplexed. At just before “tv4”, because neither of the audio packet nor picture packet has a vacant capacity for one packet, a padding packet is multiplexed.
FIG. 17
illustrates a conventional decoder for multiplexed data coded in MPEG 2 format. The decoder comprises the following elements: separator
1702
, picture data buffer
1704
, audio data buffer
1706
, reference time reproduction part
1708
, picture data decoder
1710
, audio data decoder
1712
.
The separator
1702
receives and separates a multiplexed data
1701
into a picture packet data
1703
and an audio packet data
1705
referring to the identifier attached to the packet header. The resultant separated data
1701
and
1703
are stored in the respective buffers
1704
and
1706
. At the same time, a sample value
1707
of the reference time is extracted and supplied to the reference time reproduction part
1708
, where a reference clock of the decoder is produced. The reproduction part
1708
outputs a reference time signal
1709
to the picture data decoder
1710
as well as to the audio data decoder
1712
. The picture data decoder
1710
compares the decoding time included in the picture-packet-header that is stored in the buffer
1704
with the reference time signal. When the decoding time comes, the picture data is decoded and a picture frame
1711
is reproduced. In the same manner, the audio decoder
1712
compares the decoding time included in the-audio-packet-header that is stored in the buffer
1706
with the reference time signal. When the decoding time comes, the audio data is decoded and an audio frame
1713
is reproduced.
A method of object coding has drawn attention as a new coding method. This method divides a picture into objects such as a plurality of pictures physically including background and foreground pictures as well as audio accompanying the respective pictures. The conventional coding method of picture and audio has handled a picture and audio data thereof hitherto as a whole picture and audio accompanying the picture. An advantage of this object coding method is to
Chin Wellington
Parkhurst & Wendel L.L.P.
Pham Brenda
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