Jerry,Dan gives a good explanation above in simple layman's terms.
This is called blanking, a product of NTSC video. It can be "covered" up in the upconversion process, if the Upconvertor allows it. Not all do, ours here
can. BUT, if we were running grey bars as Dan does, we'd have to make the bars a little wider to ensure you'd never see the blanking, and in the process cover up a bit of the active picture most of the time. BooHiss!
I agree with Dan that it probably won't cause a burn in problem, I tend to believe that unless you're running a plasma set or tube projector, that the
concern over burn in is excessive. I have a 35" 4x3 set here at home, and watch a lot of 16x9 material, and have had no problems with burn in.
Despite what most members here think, DTv is still in the early stages,
and we all, especially most networks, are still figuring out how to do some
of this stuff. I loaded beta software this week, for the WOLO & WCCB PSIP generators, the Dolby E decoders, program multiplexors, and the WOLO
TV-25 ASI decoders.. Point being is this stuff is still pretty much a science project that's about to become reality..unlike analog Tv which has had decades to be perfected, if that's what you'd call it..
The views expressed here are my own and do not necessarily represent those of the FOX,ABC,CBS,or CW Networks,MeTv, my employer or its parent company. Nor my wife for that matter!