HDTV programming question

[vy2005]

This may be a stupid question but why does a channel have to be in HD by the provider for you to receive the signal in HD. Let's take Time Warner for example. The don't have USA in HD but if you turn it on USA and they are broadcasting a show in HDTV, why wouldn't my HDTV receive it? Why does the provider have to have USA HD for it to broadcast through in HD? Does that make sense?

 

[mishatx]

unlike color vs. black and white (where you could watch a color program on a black and white tv without problem), HDTV and regular TV are encoded entirely differently. If you are watching on the standard channel, you are not getting the HD version of the program. If you tried to watch the HD channel on a standard TV, you would not get a picture at all.

So there's two feeds: an SD only feed, and a feed that carries HD programs.