Multiplex (TV)
Encyclopedia
A multiplex or muxA multiplex or mux (called virtual sub-channel in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 and Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, and Bouquet
Bouquet
Bouquet, a word of French origin, pronounced , may refer to:* Bouquet , a fragrance or odor, especially when used as a description of wine* Flower bouquet, an arrangement of cut flowers* Fruit bouquet, a fruits arrangement in the form of bouquet...

 in France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

) is a group of TV channels that are mixed together (multiplexed
Multiplexing
The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...

) for broadcast over a digital TV channel and separated out again (demultiplexed) by the receiver. There are two different types of multiplexes, which are closely related but not identical.

In the UK a multiplex (usually abbreviated mux) is a band of fixed width containing a number of channels. In the USA the same arrangement is often described as a channel with virtual sub-channels.

Pay TV multiplexes

Many Pay TV
Pay TV
Pay television, premium television, or premium channels refers to subscription-based television services, usually provided by both analog and digital cable and satellite, but also increasingly via digital terrestrial and internet television...

 services on cable television offer multiplex packages, in which a single service offers a number of separate channels to its subscribers. The channels may be distinct, or timeshifted
Timeshift channel
A timeshift channel is a television channel carrying a time-delayed rebroadcast of its "parent" channel's output. This channel runs alongside their parent: the term "timeshift" does not refer to a network broadcasting at a later time to reflect a local timezone unless the parent is also available...

, or may offer different views of the same event, for example overviews of a car race, the view from different drivers' cars, a view of the pits, etc. Some pay TV multiplexes offer picture in picture (PIP) capabilities to follow the various feeds simultaneously on one screen. If the hardware allows several channels in one multiplex can be viewed simultaneously.

Pay TV may be on a subscription or a pay-per-view
Pay-per-view
Pay-per-view provides a service by which a television audience can purchase events to view via private telecast. The broadcaster shows the event at the same time to everyone ordering it...

 basis.

Digital subchannels

Analog television
Analog television
Analog television is the analog transmission that involves the broadcasting of encoded analog audio and analog video signal: one in which the message conveyed by the broadcast signal is a function of deliberate variations in the amplitude and/or frequency of the signal...

 channels, whether terrestrial, cable, or satellite, are transmitted uncompressed, and always require the same bandwidth, so there is no reason not to transmit each one separately. Digital television
Digital television
Digital television is the transmission of audio and video by digital signals, in contrast to the analog signals used by analog TV...

 stations are transmitted in a compressed format, so that the bandwidth they require varies from instant to instant; it is more efficient to transmit several channels together so that they share the same bandwidth, each channel using the instantaneous bandwidth it needs, and channels currently not transmitting giving up their bandwidth to those that are. A group of channels transmitted within a particular bandwidth allocation is known as a multiplex; or the channels may be called subchannels. Sometimes, when analog transmissions are replaced by digital, the fixed bandwidth of one analog station is allocated to a multiplex; the bandwidth of one analog station is sufficient for several compressed channels.

A set top box or Integrated Digital Television
Integrated Digital Television
An Integrated Digital Television set is a television set with a built in digital tuner, be it for DVB-T, DVB-S, DVB-C, DMB-T/H, ATSC or ISDB. Most of them also allow reception of analogue signals . They do away with the need for a set top box for converting those signals for reception on a...

 is required to tune in, receive, and demultiplex a channel for viewing. A multiplex can contain half a dozen TV channels yet only uses the same space of one analog channel.

Any programs, not necessarily from the same network, can be multiplexed. Programming from a commercial network that would not otherwise be available in the station's broadcast area can be transmitted.

Digital television multiplexes vary in the number of channels that can be transmitted, based on the bandwidth of the multiplex and the broadcast quality specified for each channel. Digital terrestrial offers the least, digital cable and satellite the most bandwidth.

A single multiplex may carry conventional TV channels, radio, and teletext
Teletext
Teletext is a television information retrieval service developed in the United Kingdom in the early 1970s. It offers a range of text-based information, typically including national, international and sporting news, weather and TV schedules...

, and sometimes hidden channels carrying data.

U.S.A.

In the U.S.A the standard for over-the-air digital transmissions is ATSC
ATSC
ATSC standards are a set of standards developed by the Advanced Television Systems Committee for digital television transmission over terrestrial, cable, and satellite networks....

, digital cable is based on the worldwide DVB standard, DVB-C
DVB-C
DVB-C stands for Digital Video Broadcasting - Cable and it is the DVB European consortium standard for the broadcast transmission of digital television over cable...

 (C for cable) and transmission via satellite are based on the DVB-S
DVB-S
DVB-S is an abbreviation for Digital Video Broadcasting — Satellite; it is the original Digital Video Broadcasting forward error coding and demodulation standard for satellite television and dates from 1994, in its first release, while development lasted from 1993 to 1997...

 (S for satellite) standard, all use multiplexes to deliver various channels to the viewer. Smaller and newer commercial networks, such as The CW and MyNetworkTV
MyNetworkTV
MyNetworkTV is a television broadcast syndication service in the United States, owned by the Fox Entertainment Group, a division of News Corporation...

, are available in some markets as digital subchannels of other network affiliates rather than as standalone stations. A multiplex can also carry radio and interactive TV content.

The ATSC standard and its early adoption of HDTV is the best quality available of HDTV programming since the cable and satellite providers in the U.S.A use heavy compression to fit as many channels into their multiplexes as possible. ATSC
ATSC
ATSC standards are a set of standards developed by the Advanced Television Systems Committee for digital television transmission over terrestrial, cable, and satellite networks....

 and Free-to-air
Free-to-air
Free-to-air describes television and radio services broadcast in clear form, allowing any person with the appropriate receiving equipment to receive the signal and view or listen to the content without requiring a subscription or one-off fee...

 satellite TV is free of charge, while digital cable and Direct broadcast satellite
Direct broadcast satellite
Direct broadcast satellite is a term used to refer to satellite television broadcasts intended for home reception.A designation broader than DBS would be direct-to-home signals, or DTH. This has initially distinguished the transmissions directly intended for home viewers from cable television...

 TV do not offer any free content.
A typical American ATSC multiplex offers 3 to 4 channels, in most cases one of them is broadcast in HDTV (main TV network channel) and the rest of the channels are broadcast in SDTV.

Europe

In Europe multiplexes are used on the DVB-T
DVB-T
DVB-T is an abbreviation for Digital Video Broadcasting — Terrestrial; it is the DVB European-based consortium standard for the broadcast transmission of digital terrestrial television that was first published in 1997 and first broadcast in the UK in 1998...

 and DVB-T2
DVB-T2
DVB-T2 is an abbreviation for Digital Video Broadcasting – Second Generation Terrestrial; it is the extension of the television standard DVB-T, issued by the consortium DVB, devised for the broadcast transmission of digital terrestrial television....

 (T for Terrestrial) digital terrestrial standards, on DVB-C
DVB-C
DVB-C stands for Digital Video Broadcasting - Cable and it is the DVB European consortium standard for the broadcast transmission of digital television over cable...

 digital cable and on DVB-S
DVB-S
DVB-S is an abbreviation for Digital Video Broadcasting — Satellite; it is the original Digital Video Broadcasting forward error coding and demodulation standard for satellite television and dates from 1994, in its first release, while development lasted from 1993 to 1997...

 digital satellite. Publicly and privately owned TV networks use multiplexing to broadcast many digital channels over a few multiplexes using the various digital broadcast standards. In Europe a typical DVB-T
DVB-T
DVB-T is an abbreviation for Digital Video Broadcasting — Terrestrial; it is the DVB European-based consortium standard for the broadcast transmission of digital terrestrial television that was first published in 1997 and first broadcast in the UK in 1998...

multiplex offers 4 or more SDTV channels transmitted simultaneously; if some channels transmit only for part of the day (e.g., a children's channel during daytime, a channel with programs for adults in the evening), many channels may share the same multiplex.
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