I fear we're veering rapidly off topic here, but... On 10/10/07, Brian Butterworth <[EMAIL PROTECTED]> wrote: > > On 10/10/2007, Duncan Barnes <[EMAIL PROTECTED]> wrote: > > > > Unfortunately nobody as yet has come up with > > a way of doing a seamless (ie no macro blocking/breaks in > > transmission) switch between a main feed (e.g ITV1) and a regional > > feed (e.g. ITV Meridian) and back on the set-top box end and so it has > > to be done before the content is compressed and sent out separately. > > > Oh, yes they have... They did it years ago. It's easy with digital TV! > You don't even need the "black frame to stop the roll" you needed with > analogue - as per ITV. Auntie had the synchonised network back in the > 1980s. >
Switching between SDI signals is easy; what Duncan's suggesting is a bit trickier. At present: the BBC and ITV, and Channel 4 have satellite multiplexes which carry several channels which are the same for most of the day; they can differ when it comes to news, regional programmes and advertising. Ideally, each mux could carry a high bitrate version of (eg) ITV1 during network programming, but during regional opts (local news, ad breaks, etc), would carry each of the local streams, though probably at a lower bitrate, and the viewer wouldn't notice a thing. I *think* that DVB can do this, but changing the SI tables (which tell the receiver where to find the video and audio associated with a network) on the fly isn't an exact enough science to be able to do it with the frame accuracy desired by the broadcasters I suspect someone - BBC R&D? - has already done research into this. - martin
