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Like MPEG groups there is a DVB group - Digital Video Broadcast, made
up of interested parties, sharing information & setting the standards.
It's somewhat like the VESA group for PC graphics. DVB was set up by
the EBU (European Broadcast Union) to set the standards for digital
video transmission. They have published these via ETSI (European Telecommunications
Standards Institute) who also set standards for devices such as GSM
telephones. In fact there are several DVB standards for different transmission
media.Some of these are :
DVB-S Satellite
DVB-C Cable
DVB-T Terrestrial
DVB-SI Specification
for Service Information
DVB-CI Common
Interface for conditional access
They've
settled on using a subset of MPEG2 for their compression of the video
& audio. I've pasted in below a definition of the requirements to
be met to claim that your IRD (Integrated Receiver Decoder i.e. satellite
box) is DVB compatible :-
To be DVB compliant a Satellite or a Cable
receiver must,
according to DVB Document A001-revision 1,
at least fulfill the following key features:
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Systems
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MPEG-2 Transport Stream is used
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Service information is based on MPEG-2 Program Specific Information
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Scrambling is as defined by CA Technical Group
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Conditional Access uses the MPEG-2 CA_descriptor*
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Video
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MPEG-2 Main Profile at Main Level is used (1.5-15 Mbits/s)*
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The frame rate is 25 Hz
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Encoded pictures may have either 4:3, 16:9 or 2.21:1 aspect ratio
4:3
is the normal TV format,
16:9 is the widescreen format
and 2.21:1 is the cinemascope format that is use in the movie
theatres
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IRDs will support 4:3 and 16:9 and optionally 2.21:1 aspect ratios
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IRDs must support the use of pan and scan vectors to allow a 4:3
monitor to give a full-screen display of a 16:9 coded picture
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IRDs must support a full screen display of 720 x 576 pixels (and
a nominal full-screen display of 704 x 576)
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IRDs must provide appropriate up conversion to produce a full-screen
display of 544 x 576 and 480 x 576 and a nominal full-screen display
of 352 x 576 and 352 x 288 pixels.
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Audio |
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MPEG-2 Layer I and Layer II must be supported by the IRD |
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The use of Layer II is recommended for the encoded bitstream |
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IRDs must support single channel, dual channel, joint stereo and
the extraction of at least a stereo pair from MPEG-2 compatible
multichannel audio |
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IRDs must support sampling rates of 32 kHz, 44.1 kHz and 48 kHz |
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The encoded bitstream will not use emphasis |
Note
that American DSS, DirecTV etc. systems are NOT DVB-compliant &
won't work in Europe. I do know of an attempt by someone in the USA
to modify a European Nokia digital receiver to decode DigiiCypher2 transmissions
- but, at the time of writing, this has not been successful.
EPG
(Electronic Programme Guide)
:- A feature of most
digital satellite receivers.
Essentially
a programmable guide to what's on each channel with further program
information when supplied by the channel. Many include some quite useful
information like what's on next in addition to what's on now and a brief
description of the programme content. There's specific provision within
the Mpeg2 structure for this information to be transmitted; however
not all operators make use of it.
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