[interestednovice]

Interesting times, indeed!

Originally, BBC One HD launched in a hurry so it was set up with new playout and the entire infrastructure was as if an entirely new channel was being launched. Later on, around a year after launch, SD switched to being a downscaled version of HD output. Not long after, the original nations variations launched. “BBC One Network” (SD) then no longer existed as a separately produced service, as a downscaler simply produced the feed. BBC One HD had a DOG added via a caption generator downstream of the split so only HD viewers saw it. A similar approach may be being used now, with a basic graphic generator.

Of course, in those days, BBC One HD network always had the red screen in England; regional variations also were produced differently as the signal physically when to the region (carrying network feed) and back to coding and mux (so was always sent “through the region” in a way that it isn’t now - with opting in and out physically happening at the region site). As part of the preparation for the HD regions upgrade, play out was changed so that regional opting is now controlled by a “switch” in playout instead, but regions can remotely control the switch - allowing them to maintain some autonomy if an emergency opt is needed. So there is no longer a need for the feed to go via the region and back again before coding and mux.

I say all that to point out that things have certainly been changing throughout, but not to the point ordinary viewers would have noticed. The DOG on BBC One HD is long gone though, thankfully!