Editing Multiplexing (section)

==Application areas==

===Telegraphy===
The earliest communication technology using electrical wires, and therefore sharing an interest in the economies afforded by multiplexing, was the [[electric telegraph]]. Early experiments allowed two separate messages to travel in opposite directions simultaneously, first using an electric battery at both ends, then at only one end.

[[Émile Baudot]] developed a [[time-multiplexing]] system of multiple [[David E. Hughes|Hughes]] machines in the 1870s. In 1874, the [[quadruplex telegraph]] developed by [[Thomas Edison]] transmitted two messages in each direction simultaneously, for a total of four messages transiting the same wire at the same time. Several researchers were investigating [[acoustic telegraphy]], a [[frequency-division multiplexing]] technique, which led to the [[invention of the telephone]].

===Telephony===
In [[telephony]], a [[customer]]'s [[local loop|telephone line]] now typically ends at the [[remote concentrator]] box, where it is multiplexed along with other [[telephone line]]s for that [[neighborhood]] or other similar area. The multiplexed signal is then carried to the [[telephone exchange|central switching office]] on significantly fewer wires and for much further distances than a customer's line can practically go. This is likewise also true for [[digital subscriber line]]s (DSL).

[[Fiber in the loop]] (FITL) is a common method of multiplexing, which uses [[optical fiber]] as the [[Backbone network|backbone]]. It not only connects [[Plain old telephone service|POTS]] phone lines with the rest of the [[PSTN]], but also replaces DSL by connecting directly to [[Ethernet]] wired into the [[home]]. [[Asynchronous Transfer Mode]] is often the [[communications protocol]] used.{{citation needed|date=June 2018}}

[[Cable TV]] has long carried multiplexed [[television channel]]s, and late in the 20th century began offering the same services as [[telephone companies]]. [[IPTV]] also depends on multiplexing.

===Video processing===
{{Main|Demultiplexer (media file)}}
In [[video]] editing and processing systems, multiplexing refers to the process of interleaving audio and video into one coherent data stream.

In [[digital video]], such a transport stream is normally a feature of a [[container format]] which may include [[metadata]] and other information, such as [[subtitles]]. The audio and video streams may have variable bit rate. Software that produces such a transport stream and/or container is commonly called a multiplexer or '''muxer'''. A '''demuxer''' is software that extracts or otherwise makes available for separate processing the components of such a stream or container.

===Digital broadcasting===
In [[digital television]] systems, several variable bit-rate data streams are multiplexed together to a fixed bit-rate transport stream by means of [[statistical multiplexing]]. This makes it possible to transfer several video and audio channels simultaneously over the same frequency channel, together with various services. This may involve several [[standard-definition television]] (SDTV) programs (particularly on [[DVB-T]], [[DVB-S2]], [[ISDB]] and ATSC-C), or one [[HDTV]], possibly with a single SDTV companion channel over one 6 to 8&nbsp;MHz-wide TV channel. The device that accomplishes this is called a [[statistical multiplexer]]. In several of these systems, the multiplexing results in an [[MPEG transport stream]]. The newer DVB standards DVB-S2 and [[DVB-T2]] has the capacity to carry several [[HDTV]] channels in one multiplex.{{citation needed|date=June 2018}}

In [[digital radio]], a multiplex (also known as an ensemble) is a number of radio stations that are grouped together. A multiplex is a stream of digital information that includes audio and other data.<ref>{{cite web|url=https://www.radioandtvhelp.co.uk/interference/rtis_radio/DABmuxes_DABradio|title=All about DAB multiplexes|work=Radio & Television Investigation Service|publisher=[[BBC]]|access-date=17 June 2018}}</ref>

On [[communications satellite]]s which carry [[broadcast]] [[television network]]s and [[radio network]]s, this is known as '''multiple channel per carrier''' or '''MCPC'''. Where multiplexing is not practical (such as where there are different sources using a single [[transponder]]), [[single channel per carrier]] mode is used.{{citation needed|date=June 2018}}

===Analog broadcasting===
In [[FM broadcasting]] and other [[analog signal|analog]] [[radio]] media, multiplexing is a term commonly given to the process of adding [[subcarrier]]s to the audio signal before it enters the [[transmitter]], where [[modulation]] occurs. (In fact, the stereo multiplex signal can be generated using time-division multiplexing, by switching between the two (left channel and right channel) input signals at an ultrasonic rate (the subcarrier), and then filtering out the higher harmonics.) Multiplexing in this sense is sometimes known as '''MPX''', which in turn is also an old term for [[stereophonic]] FM, seen on [[stereo system]]s since the 1960s.