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QUality Of Video and Audio for DIgital television Services

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The International Standards Organization/International Electrotechnical Commission Moving Picture Expert Group (ISO/IEC MPEG) Signal Switcher Standard calls for the use of serial links to make the interconnection between the pieces of equipment of digital television chains. The management of such high rate links is very delicate. The operators prefer to use parallel links at the rate of 27 Mhz, making the selection of relevant output data inside the transport stream easier. The MPEG2 signal switcher simultaneously allows for commuting and dispatching digital television channels. The switcher permits the selection of a digital television parallel signal among the 2 available on the input and dispatching on 3 to 6 outputs. The parallel inputs and outputs may be either emitter coupled logic (ECL) signals LVDS signals. The whole set is integrated in an aerated rack of standard height with supply and signal presence display lights with a switch for the selected input. As an option the mains can be backed up. Each input-output is independent. The secondary group has an add-on input allowing for cascading all the racks in one single installation. The lack of the MPEG signal is detected by the MPEG stream analysis. It is displayed on the front panel. The commands may be given either manually on the rack itself or remote through a personal computer type microprocessor, cascade-linked to the set of racks with RS 232 links. Commutation is carried out automatically or manually on the main group depending on the MPEG stream. The command of the secondary group is independent from that of the main group which allows for controlling inputs whatever the main group status. The rack may be operated at each intermediate stage of the digital television chain.
A metrology tool has been developed which is a processing software of the Ensemble Transport Interface (ETI), Fast Information Channel (FIC) and Packet DATA channel carried in the DAB transport multiplex. It can be connected to the output of an Ensemble Stream and/or Packet Multiplexer, or to the input of a COFDM encoder. The software runs on a personal computer (PC) with DOS which controls one Data Extraction board. Real time analysis is available and can be stopped on breakpoint conditions. Offline processing can be done on Nxframes stored before and after the breakpoint condition. The software offers a package of functions which allows the control and the check of ETI, FIC and Data Packet specifications. Other characteristics include: offline ETI demultiplexing (FIC, Audio and Data subchannel); Hexa. display of each Audio/Data Stream frame by frame; packet and data group analysis and display; DAB multiplex and ensemble organization display; online help, trace files; Hexa or FIG search (with or without extension); store and load ETI files; ETI frame dating.
A digital audio broadcasting tool has been developed which can record and play Audio sequences with or without associated data. All data formats and bit rates are accepted. 2 digital input/output interfaces are accepted WG1/WG2 and Ensemble Transport Interface (ETI), from one up to three programs. The system has an internal clock but can be synchronized with an external clock.
The Moving Picture Expert Group (MPEG)2 binary flow generator is a tool providing a broadcast for multiplexed programmes. This tool permits diverse scenarios concerning the MPEG2 reference flow to be generated from Packetized Elementary Stream (PES) type information sources which may be used to validate some components within the framework of a contract for MPEG2 multiplexer realization. In practice, the analyser is inserted in a production/broadcast chain of digital television signals, between the encoding systems delivering elementary PES source files and the broadcast system. The generated flows may be included in conditional-access television programme distribution and, therefore, be encrypted in compliance with the EUROCRYPT standard. The analyser may thus be interfaced with the Subscriber Authorization System and the Access Controller. The generator uses PES audio and video plus private data binary files on input in order to produce an Multiple Program Transport Stream (MPTS) transport flow in the form of a binary file and of a text file describing the flow. The whole set of these elements may be managed by an administrator common to the whole test chain. The software functions are as follows: management of the administrator parameters corresponding to the multiplexing configuration; scrambling of transport packets; linking of PES flows; cutting of PES packets; Program Specific Information (PSI) generator on the service channel; decoding of PSI flow sections; cutting out of PSI sections; dynamic evolution of the service channel content during the multiplexing; logical construction and physical encoding of transport packets; MPEG2 transport multiplex in order to generate a single Program Transport Stream or an MPTS. The MPEG2 flow generator has been developed on a PC/WINDOWS platform. Main applications for the generator are: adjustment of experimental digital television chains; adjustment of digital television production/broadcast/distribution chains.
The success encountered by the International Standards Organization Moving Picture Expert Group 1 (ISO MPEG 1) Audio standard has permitted the marketing of many coding boards and software. Faced with the difficulties that the developers had for decoding some binary flows, a parser has been developed which detects any nonconformity of a compressed file regarding the standard. The ISO MPEG1 Audio standard does not call for a special coding algorithm, on the contrary it defines precisely the syntax of the binary flow coming out of the coder, and, therefore, calls for several constraint types: it forbids some values for the coded samples, or for the lateral information; it keeps the information within a strictly limited space; it appeals for a special management of the stuffing bits; it authorizes an error detecting code for the most sensitive information. Depending on any of these syntax errors and where they are placed, the functioning of the decoder may become erratic. The parser is coded in C-ANSI language that may be compiled on any of the following machines: PC, MAC, indigo station, SUN, and even a processor with fixed-point arithmetic. It gives an especially quick executable program. Whenever a noncompatibility has been detected, an error file is created, beginning with a recall for the correspondences between the error messages and the parts of the ISO standard that are concerned, and after that a precise localization of each noncompatibility. The analyser layout is in conformance with the 11172-4 ISO standard which defines the compatibility with MPEG1 Audio standard. Main applications of this technology are in compatible coders for use in broadcasting or for multimedia applications with broadcasting of binary flows.

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