About EPG Or Electronic Program Guide
EPG stands for Electronic Program Guide.As its name indicates that it is a program guide that is electronically available provides all the information about the program currently running and following.Thus the user can decide what to watch. Electronic Program Guide is implemented in Television , Radio and also in other multimedia applications.which displays the information about currently running program and upcoming program also.
In Digital Headend System the Setup Box understands the EPG and it displays on the TV. EPG is basically list of TV channel programs which are provided by the broadcasters and implemented in digital headend system. Each Tv channel have its separate EPG. The broadcaster can provide EPG in three formats XML,CSV and HTML.
EPG Implementation in Digital Headend System
In Digital headend system there are many external devices used for to insert the EPG these are named as EPG Builder,EPG Inserter and EPG Generator. The EPG data is carried out through the EIT (Event Information Table) table. This EIT table comes under SI tables. The HEX value for this EIT table is 0x0012 or 18 in Decimal.Thus EPG is inserted through these SI tables in the Transport stream. Basic block diagram for EPG insertion in Digital Headend System is mentioned below, 
Insertion Of EPG In Digital Headend System
As shown above in the figure there are two encorders. These encorders are encoding the Composite Signal. Composite Signal is called the audio video signal in this case which comes threw our decorders.Now this composite signal is encoded by the encorders which can generate SPTS (Single Program Transport Stream) or MPTS (Multi Program Transport Stream).This SPTS goes as input into the multiplexer which multiplexe and gives MPTS output. PSI SI generator generate the PIDs and EPG generator the EPG these two data goes into the multiplexer. Working of EPG generator is shown below, 
Working Of EPG Generator
As shown above in the figure EPG source may be in .XML , .CSV or .HTML format. This EPG source file send by the broadcasters we copy in the local storage of the EPG generator from where EPG generator automatically collect it and generate EIT or Event Information Table. Lets describe some important descriptor used in EPG,
(1) content_descriptor content descriptor contains the information about the Genre of Event. It contains the table of gener where a single event can have more than one genre
(2) component_descriptor component descriptor provide the information about the event like format of subtitle,aspect ratio format and audio language availability etc.
(3) short_event_descriptor short event descriptor contains the event title and event description. this field can contain maximum 255 characters.short event descriptor is a basic descriptor.
(4) extended_event_descriptor extended event descriptor contains the description of events or synopsis in text format. character length for is 3984.
(5) parental_rating_descriptor parental rating descriptor contains the level of content, what parents wants to their child to watch. This is all about the Electronic Program Guide.
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