(the original DVB-T could mux 8 or 9 SD channels, but only one HD and one SD, if I remember correctly. with HD channels, the channels need more bandwidth, and you can't bundle as many of them any more. The trick is pretty much that the multiplex is so fast that the channel only needs about 1/9th of the available bandwidth to be able to send enough information to keep it running for a second at a time. It sends some control information (time of the day, the name of all the channels and their place in the mux, the encryption technique of the channels, the TV guide, and some other technical shit), a chunk of what's on channel 1, a chunk of what's on channel 2, a chunk of what's on channel 3 (and so on.), and then it starts over with the mux control information. When you tune in to a specific frequency (no matter if you do that in a cable tv network, on a satellite position or with a terrestrial antenna, you'll be presented with a palette of channels that are available on that specific frequency. DVB, and all of it's substandards, are multiplexing standards. It's very common in digital tv (and radio!) broadcasting techniques. Multiplexing is a common term for when an communication medium contains several sets of individual information at the same time.
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