Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
2000-10-05
2002-07-16
Vu, Huy D. (Department: 2665)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S443000
Reexamination Certificate
active
06421359
ABSTRACT:
BACKGROUND OF THE INVENTION
The International Organization for Standardization (ISO) has adopted a standard (ISO/IEC 13818-1) that addresses the combining of one or more “elementary streams” of video and audio, as well as other data, into single or multiple streams suitable for storage or transmission. The ISO/IEC 13818-1 standard, hereinafter referred to as the “MPEG-2 Systems” standard, is described in detail in the ISO draft document “Generic Coding of Moving Pictures and Associated Audio”, ISO/IEC JTC
1
/SC29/WG11 N0801 ( Nov. 13, 1994), which is incorporated herein in its entirety by reference.
The MPEG-2 Systems standard defines an individual coded video, audio or other coded bitstream as an “elementary stream”. The contents of an elementary stream may be broken into a sequence of discrete units, in which case the elementary stream is structured as a Packetized Elementary Stream (PES). The individual units, or packets, are known as PES packets, which can be of large and variable size. The MPEG-2 Systems standard defines generic structures for PES packet formats and specifies particular rules for creating PESs from digital video and audio elementary streams. Allowance is made for creating PESs for private data formats, i.e., data formats not defined by the MPEG-2 Systems standard.
The MPEG-2 Systems standard defines two methods of creating a multiplex of PESs. In a Program Stream (PS), all components in the multiplex are assumed to belong to a single “Program”, that is, a collection of elementary streams which may sensibly be presented as a unity to a user, all components being referenced to a common time base, together with certain coordinating control information. PES packets from component PESs are multiplexed by PES packet. The PS is rigidly structured so that at most one PES of a specified format may carry a private data elementary stream.
In a Transport Stream (TS), the components of the multiplex may belong to many programs. Each PES is assigned a “packet identifier” (PID). A sequence of packets identified by the same value of the PID field represents a single service component, typically a video or an audio component, or a user data component. The PES packets are broken into small, fixed-size units called transport packets, which may be multiplexed with transport packets from other PESs. The Transport Stream is transmitted at a constant rate, the transport rate, which is sufficient to accommodate the bandwidth requirements of all components carried within the Transport Stream. Since the transport rate may, either momentarily or in aggregate, exceed the bandwidth requirements of the constituent component, the MPEG-2 Systems standard has reserved PID 0×1FFF as the “null PID”. Packets in this PID are “null packets” and do not carry any component. An MPEG decoder may discard them with impunity.
Coordination and control of the PESs and the Programs in the TS is managed via control data called Program Specific Information (PSI). PSI is structured as a set of tables according to a section format which differs from and is incompatible with the PES packet. The defined tables include the following:
A Program Association Table (PAT) is carried in PID 0, which is reserved exclusively for this purpose. The PAT identifies the Programs or services available via a program_number field, and, for each service, identifies the PID carrying the PMT applicable to that service.
A Program Map Table (PMT) for each service is carried in a PID identified within the PAT. The PMT identifies all the components belonging to the service and may provide additional information describing the components.
A Conditional Access Table (CAT) is carried in PID 1, which is reserved exclusively for this purpose. The CAT identifies PIDs carrying authorization streams for decoders implementing different conditional access systems. This information may include Entitlement Control Messages (ECMs) or Entitlement Management Messages (EMMs) used for encryption and authorization.
In addition, the Digital Video Broadcasting (DVB) committee has defined a number of additional tables for transport of Service Information (SI), including a Service Definition Table (SDT).
Thus, a Transport Stream can be understood as a multiplex of service components combined with descriptive service control information. However, the MPEG-2 Systems standard does not define how the Transport Stream multiplex is to be formed.
SUMMARY OF THE INVENTION
It is desirable to be able to combine two or more transport streams into a single transport stream that contains all of the components of the source transport streams. A problem encountered in combining transport streams is that the transport stream PIDs associated with one source stream typically conflict with the PIDs associated with one or more other source streams. Other identifying information, such as the program_number, assigned to a service may also conflict with that assigned to a service in another transport stream. Additionally, multiplexing two transport streams may cause embedded timing information, such as the Program Clock Reference (PCR), to be rendered inaccurate.
The above and other problems are solved by the multi-service transport multiplexing apparatus and method of the present invention. The present invention defines a process for creating a transport stream by addition of services, one at a time, to a pre-existing transport stream multiplex. The invention provides a capability for building a common set of service control information from the service control information tables of the individual streams being combined that avoids PID conflicts.
Accordingly, apparatus for multiplexing transport streams includes first and second transport demultiplexers for demultiplexing first and second input transport streams to their respective service components and service control information tables. Each demultiplexer filters the respective service components and service control information tables according to a particular filter set that specifies PID processing actions. A processor coupled to the first and second demultiplexers comprises means for examining the first and second service control information tables to determine whether any PID of one of the first and second transport streams overlaps or conflicts with any PID of the other of the first and second transport streams. The processor further includes means for generating output service control information tables from the first and second service control information tables that have been modified to avoid any overlapping or conflicting PIDs. The processor further provides the first and second filter sets to the first and second demultiplexers based upon the output service control information tables. A transport remultiplexer coupled to the processor and the first and second demultiplexers multiplexes the output service control information tables and the filtered first and second service components to provide an output transport stream.
According to an aspect of the invention, the processor changes or discards PIDs that overlap or conflict in the input transport streams.
According to another aspect of the invention, an encoder is combined with a transport multiplexer to provide an encoder/multiplexer. The encoder encodes a program source to provide a local transport stream. The transport multiplexer multiplexes the local transport stream with an input transport stream to provide an output transport stream. First and second encoder/multiplexers are series coupled wherein the output transport stream of the first encoder/multiplexer is coupled to provide the input transport stream to the multiplexer of the second encoder/multiplexer. Additional encoder/multiplexers can be series coupled to provide a daisy-chain configuration. In this manner, a general solution to the generation of a multi-service transport stream can be provided from the multiple local streams. In a preferred embodiment, a bypass circuit couples the input transport stream directly to the output transport stream which is activated in the event of failure of
Bennett Christopher J.
d'Oreye de Lantremange Maximilien
Hamilton Brook Smith & Reynolds P.C.
Ho Duc C.
Tiernan Communications, Inc.
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