Originally Posted by nctarheel
I have read from various sources that in order for a station to broadcast a program in HD, a switch must be flipped, literally. If the flip is not switched to HD, then an HD program will be pillarboxed or windowboxed. What would happen if the HD switch was not turned off, and was activated whilst a non-HD program is being shown?
Technically three things must happen
1) The content must be produced (encoded, etc etc) in a HD resolution (usually 720 or 1080i for broadcast content) and the equipment that transmits the content must be capable to passing along that content
2) if any sort of VCR, DVR, Digital Converter etc is in use it has to be able to receive that signal and output it in a format usable by the viewer (i.e. if you've got a TIVO Series III or HD, you can set it to 420 and watch HD content on a SD TV...)
3) The TV has to be set up depending on the user's preference (720p, 1080i etc)
Generally most HD channels *will not* show all their content in HD. Local daytime TV and commercials will usually be in SD and this will not cause the TV to black out... what may happen though, depending on your equipment and settings is you may see a SD picture floating in the middle of a 1080i screen etc. I get this often as this is what our HD cable boxes do by default - HD channels are sending information for a full 1080i picture, but SD is send down centered in the middle. This is corrected by changing the box or the TV setup to stretch programming in SD resolution.
Because HD requires much more detailed information it's much more likely to black out if there's a loss of signal... so sudden changes in signal are likely to be most visible on HD channels rather than SD channels.
Hope that helps a bit