Multiplex (television)

A multiplex or mux (called virtual sub-channel in the United States and Canada, and bouquet in France) is the popular term used for the grouping of program services that are sub-grouped as interleaved data packets for broadcast over a network or modulated multiplexed medium, which are split out at the receiving end. There are two different types of groupings, which are closely related but not identical.

In the United Kingdom, a terrestrial multiplex (usually abbreviated mux) has a fixed bandwidth of 8 MHz CODFM of interleaved H.222 packets containing a number of channels. In the United States, a similar arrangement using 6 MHz 8VSB is often described as a channel with virtual sub-channels.

Many pay television services on cable and satellite television offer program service packages, in which a single provider offers a number of separate channels to its subscribers. The channels may be distinct in regards to the programming format (for example, one channel offering comedy programming and another carrying action and adventure films), be timeshifted, or offer different views of the same event (such as overviews of a car race, the view from different drivers' cars or a view of the pits). Some pay television program services 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 television multiplexes may be purchased on a subscription or a pay-per-view basis.

Analog television channels, whether terrestrial, cable or satellite, are transmitted as a single program service uncompressed at the same fixed bandwidth, which fills the entire bandwidth available. Digital television channels can be interleved and are in a highly compressed format, so that the bandwidth they require varies due to the bitrate provided to each channel; it is more cost efficient to transmit several channels together so that they share the same bandwidth, each channel have carefully constrained bitrates allocated, so that the sum of all channels fill the fixed bandwidth provided. A group of program services transmitted within a particular bandwidth allocation is erroneously 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 broadcast is allocated to the program services; the bandwidth of one analog broadcast is sufficient for several compressed channels.

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