On 10/10/2007, Richard Cartwright <[EMAIL PROTECTED]> wrote: > > > On 10/10/07 19:24, "Brian Butterworth" <[EMAIL PROTECTED]> wrote: > > > But it could be done on analogue - you could never see the join in the > switch to regional programmes on the BBC even back as far as "Sixty > Minutes", so it MUST be possible. > > On analogue Satellite? I don't think so. >
Of course not on analogue satellite! It only ran October 83-July 84, a good five years before Sky launched. I was simply pointing out that the delicate timing that was required to switch to and from a BBC region on analogue terrestrial television with a CROSS FADE was done back in October 1983. It seems reasonable to me that a digital system should be able to do it 23 years later on dsat, as long as retuning to another transponder. After all, the regional join works very well on *digital* terrestrial ... > the same way as it did on analogue terrestrial. Why? Because a different > video stream is fed to the coding and mux for the transmitter in each > region. Regionality on terrestrial broadcasting is achieved through plain > and simple video mixing at broadcast presentation. This form of regionality > has the side effect that a viewer who lives on the wrong side of a hill near > a region's border often gets the wrong region! > Ah, but it's not that simple, is it? You have to have your whole timing system synced up correctly otherwise you get a frame-roll on analogue and a frozen frame on digital. In contrast, satellite transponders cover the whole of the UK – different > ball game to your "Sixty Minutes" scenario. > The satellite system simply uploads all of the post-regional mix of all the regions and sticks them on several different transponders. To watch a region on satellite you watch one of these streams. In fact it is identical to the "Sixty Minutes" scenario. In general, a set-top-box is not video mixing hardware and the DVB > broadcasting standards are not designed to synchronise frame-accurate edits > between streams ... especially streams on different transponders that > require a frequency change when you only have one tuner! > I did say that in fact. If the MPEG-2 streams collapse, the "opportunistic data" on the interactive > systems could claim all the spare bandwidth automatically.... > > > You can't run an interactive service with that kind of interrupted > bandwidth ... "we interrupt this match at Wimbledon because Scotland and > London have some regional programming now". Automatic opportunistic > insertion of data for interactive services is technically hard to do, but > even harder is finding an editorial requirement for an interactive service > with random holes punched through the middle of its bandwidth. > That's why I said "opportunistic data" and not "interactive video streams". What is far more realistic is the possibility to download programmes and > data to a PVR using spare broadcast capacity, perhaps combined with the > delivery of ultra local programming via a broadband link. These pushed PVR > programmes could be SD, HD, interactive features (like DVD extras), games > etc.. > Wouldn't really benefit the 8 million existing users... however, it would be handy for a HD version of BBC One, BBC Two as they could switch back the SD quite happily for regional news, at least on satellite. For example. transponder 46 has BBC One West Midlands/North West/East Yorks+Lincs/Yorks/East Midlands/East. If these could be "redirected" using the existing Sky boxes AND the new BBC/ITV Freesat boxes to use a single SD stream when these regions are showing exactly the same programmes, this would give plenty of bandwidth for a HD BBC One in the same space, as the current BBC HD service shares with two SD feeds on transponder 50. Richard -- *Dr Richard Cartwright *media systems architect *portability4media.com * [EMAIL PROTECTED] mobile +44 (0)7792 799930 -- Please email me back if you need any more help. Brian Butterworth www.ukfree.tv
