Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1998-09-28
2002-11-05
Hsu, Alpus H. (Department: 2733)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C348S472000, C348S423100
Reexamination Certificate
active
06477185
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a demultiplexing and decoding apparatus which receives multiplex packet data, formed by compressing and encoding video data and audio data by high-efficiency coding means and packetizing and multiplexing the compressed and coded data, and more particularly, to a demultiplexing and decoding apparatus which demultiplexes the multiplex packet data and decodes necessary code data.
For handling an video signal and an audio signal (hereinafter referred to “A/V data”) in digital satellite broadcasting, cable television and the like, a coding method for digital-coding the audio/video signal to reduce spatial and temporal redundancy to reduce the amount of data is widely used. As an example of this high efficiency coding means, a so-called MPEG method standardized by ISO/SC29/WG11 is well known. In the MPEG method, the code data multiplexing is also standardized in the ISO/IEC13818-1: 1994“Information Technology—Coding of Moving Pictures and Associated Audio—Part 1: Systems”.
FIG. 11
shows an example of a transport stream (TS) defined in the MPEG system.
In FIG.
11
(
a
), data in the TS is included in a 188-byte fixed-length packet called a TS packet. Upon actual transmission, error-correcting codes are added to the TS packet.
The TS packet has a header which begins from a 1-byte sync word and a 13-bit packet identifier (PID). The subsequent part is called a “payload” including transfer data. Further, an extension header called “adaptation field” is added immediately subsequent to the header, in accordance with necessity. The adaptation field includes program clock reference (PCR) data necessary for reproduction of a system clock and the like.
On the receiving side, the system clock is reproduced by interpreting the PCR data. This realizes a system where the clock frequency is locked with the transmitting side, in which decoding time, output time and buffering speed can be managed in accordance with the assumption by the transmitting side.
The payload includes a program element such as A/V data of a program, as shown in FIG.
11
(
b
), or includes additional information such as PSI (Program Specific Information) data indicative of packet multiplex status and a program table, as shown in FIG.
11
(
c
) . The payload of each packet is a data portion of continuous data as shown in FIG.
11
(
b
) or
11
(
c
) (indicated with a broken line in association with FIG.
11
(
a
)).
In a case where the payload is as shown in FIG.
11
(
b
) the stream of the coded program element is packetized (this stream is referred to as a “PES (Packetized Elementary Stream) packet”, and the header of the PES packet includes data indicative of the type of program element, data indicative of the PES packet length, and DTS (Decoding Time Stamp) data indicative of time at which the program element is to be decoded, PTS (Presentation Time Stamp) data indicative of time at which the decoded program element is to be presented, and the like.
Further, as the program element, closed caption data to superimpose subtitle information on a decoded video image in accordance with an audience's request, additional A/V data outputted in synchronization with the decoded A/V signal and the like are used as well as the above-described program A/V data. These program elements are outputted in controlled output timing based on the PTS data.
In a case where the payload is as shown in FIG.
11
(
c
), the additional information is divided in section units, and data is formatted for each section. Necessary PSI data and other additional information can be obtained by interpretation in accordance with the format.
The PSI data has a hierarchical table structure, and includes PMT (Program Map Table) data where the correspondence between the element and the PID data is described for each program, PAT (Program Association Table) data where the correspondence between the PMT data and the PID data is described, and the like.
Further, a received TS packet may be encrypted such that a particular audience can decode the data. In this case, descrambling key information and the like are transmitted in section units. Such descrambling information may be ECM (Entitlement Control Message) data including descrambling key information for each program, EMM (Entitlement Management Message) data including individual receiving-machine based descrambling key information, CAT (Conditional Access Table) data indicative of the correspondence between the ECM data and each program, or the like.
Generally, as the additional information, data called electronic program guide (EPG) or the like managed in section units is transmitted. On the receiving machine side, a graphical user interface (GUI) for program selection by a user is constructed or a program reservation system is constructed by visualizing the information and outputting the information to a display screen.
Examples of a system to receive a transport stream (TS), modulated and transmitted via a medium such as CATV or digital satellite broadcasting, and to demultiplex and decode the received TS are disclosed in Japanese Patent Application Laid-Open Nos. 8-275151 and 8-265746.
FIG. 12
is a block diagram showing an example of a conventional demultiplexing and decoding apparatus for coded A/V data. In
FIG. 12
, reference numeral
1
denotes an input terminal;
2
, a demodulator-FEC decoder;
3
, a transport demultiplexer;
30
, a descrambler;
31
, a PID filter;
32
, an A/V buffer;
33
, a decoder I/F,
34
, a PST buffer;
35
, a bus I/F;
36
, a PID table,
37
, an STC (System Time Clock) counter;
4
, an audio decoder;
5
, a video decoder;
6
, a CPU;
7
, a RAM;
71
, a working area;
72
, a TS packet buffer area;
8
, a ROM;
9
, a system clock generator;
10
, a user I/F;
11
, an OSD processor;
12
and
13
, DAC's (Digital-to-Analog Converters); and
14
and
15
, output terminals.
In
FIG. 12
, a signal tuned to a desired channel by means which is not shown, and received by an antenna or the like, is inputted from the input terminal
1
and supplied to the demodulator-FEC decoder
2
. The demodulator-FEC decoder
2
decodes the input signal and performs error correction using the error correction codes in the transport stream, and supplies the signal to the transport demultiplexer
3
. In the error-corrected transport stream, a plurality of programs are multiplexed.
In the transport demultiplexer
3
, the descrambler
30
appropriately performs descrambling on the supplied transport stream, and supplies the transport stream to the PID filter
31
. In the PID filter, a packet including a set of A/V element corresponding to a desired program, desired PSI and an additional information signal are selected and extracted. Upon packet extraction, data within the PID table
36
, in which PID's to be selected are set, are sequentially read out, and one PID coincides with the PID of the input TS packet is selected.
Among the input TS packets, a program provided only to a particular audience or the like is encrypted. The descrambler
30
descrambles the encryption. Further, a TS packet including PCR data is transferred from the PID filter
31
to the STC counter
37
. The STC counter
37
counts the STC initialized with the PCR by the system clock, and outputs a control signal to the system clock generator
9
such that the difference from the sequentially-arriving PCR data is reduced. The system clock generator
9
generates a system clock as a system control reference clock based on the control signal.
Among the packets demultiplexed by the PID filter
31
, a packet including coded A/V data as a desired program element is temporarily stored in the A/V buffer
32
, and transferred via the decoder I/F
33
to the audio decoder
4
and the video decoder
5
. The audio decoder
4
decodes the supplied coded audio data in accordance with the MPEG method, and outputs the data as a digital audio signal. The video decoder
5
decodes the supplied coded video data in accordance with the MPEG
2
method, and outputs the data as a digital vi
Eda Takanori
Ishinabe Iwao
Komi Hironori
Oku Masuo
Ooishi Tomohisa
Hitachi , Ltd.
Hsu Alpus H.
Mattingly Stanger & Malur, P.C.
Tran Thien D
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