I think we may have a communications breakdown. Does replacing channels with programmes alter the sense?
I'll try again.
Unlike analogue TV where each TV channel - BBC One, BBC Two, ITV, C4 etc. was broadcast on its own frequency - and thus a single tuner could only receive one channel at a time, DVB-T/T2 digital television sends out high bitrate data streams on frequencies, and each of these high bitrate data streams (called a transport stream) on a given frequency carries multiple channels simultaneously. This transport stream contains individual smaller data streams containing video, audio, subtitles, EPG, Red Button etc. data on its own uniquely identified sub-stream, and an index so the receiver knows how to combine them into a channel.
In the UK we have 6 of these high speed data streams being broadcast on 6 frequencies in each area (excluding local TV) - which are called multiplexes or muxes - and together they carry a large number of channels. (Some poor reception areas may only get the 3 public service frequencies)
The BBC has an SD mux (BBCA or PSB1) which carries all the BBC SD TV services and radio services on a single frequency delivering 24Mb/s of data - but each channel will only use 2-3Mb/s on average to deliver sound and video. (ITV and C4 share another frequency D34 or PSB2 - which carries many of the ITV and C4 SD services and also carries the main SD C5 service)
Therefore if you have a suitable DVB-T/T2 PC tuner, you can tune to the single BBC SD frequency, and a single tuner can deliver every BBC SD TV and radio service to your PC for you to record or watch live - meaning you could watch BBC One SD live, whilst recording BBC Two SD and BBC Four SD for later viewing, all with the same tuner.
There is just one DVB-T2 mux in the UK (outside of Northern Ireland) called BBCB or PSB3. This carries all the Freeview HD channels in a 40Mbs data stream (each channel averages around 3.5Mb/s but can peak up to 13.5Mb/s as they dynamically share the 40Mb/s pool of data).
Again if your USB tuner is capable of passing the full 40Mbs stream to your computer, you can watch ITV HD live, whilst recording C4 HD, BBC One HD and BBC Two HD for example - all using just one tuner. Or you can watch use a single tuner on a single TV Headend server to watch BBC One HD in your living room on one computer, whilst watching BBC Two HD in another room, all streaming from one tuner.
This is the really clever thing about digital TV - it no longer needs a tuner per channel, just a tuner per frequency. TV Headend is clever enough to cope with this - which makes it a really powerful solution.
Some tuners have a half-way house where they can't send the full data stream - but can hardware filter a certain number of data streams still - so may let you pass two or three channels rather than all of them, or just one of them.
