Originally posted by mpg
A little background on why some programs have black bars on the left and right side of the picture... and some don't.
All commercial Philadelphia TV stations only use a High Definition DTV encoder for broadcasting 24-hours a day. WHYY has both a Standard Definition and a High Definition encoder. WHYY uses the Standard Definition decoder during the day and is currently retransmitting their Channel 12 signal. Because they are using a Standard Definition encoder, your DTV receiver and/or TV can change the picture to fill the screen. In the evening WHYY is using their High Definition encoder, the same as all the Philadelphia commercial TV stations, and retransmitting PBS's HD programming. Because the commercial TV stations are always using a High Definition encoder, when the program is not HD & 16:9, then the HD encoder upconverts the 4:3 programming so that the HD encoder can broadcast the signal. This upconverting adds the black bars on the left and right side of the screen. It's basically telling your receiver that the programming is HD & 16:9. However, to maintain the 4:3 aspect ratio, the black bars need to be added. In summary, because the commercial stations only use an HD encoder, if the programming is not HD/16:9, then you're going to get black bars on the left & right. And you won't be able to trick your DTV receiver into stretching the picture because it already thinks it's getting a 16:9 picture. If TV stations wanted to, they could stretch the 4:3 picture to 16:9, or any variation there of, before broadcasting through the HD encoder. This could fill your screen, but the aspect ratio would be messed up and not pleasing to watch.
Hoepfully this answers a few questions.
The question is, why is 4:3 content (non-HDTV content) transmitted using the HD encoder? Since it is 4 x 3 and not HDTV, use the SD decoder for that content (so we can fill the screen easily) and switch to the HD encoder only for HDTV broadcasts (HDTV content). Wouldn't that be the best of both worlds? Do you lose anything with 4 x 3 programming when an SD encoder is used (or do you gain anything when 4 x 3 programming is tranmsitted with an HD encoder)? If not, use the SD for 4 x 3 and the HD for HDTV.
Or is there any way that the HD encoder can be set to NOT transmit black bars and not stretch the 4 x3 material?
By the way, you can (at least with my set top box), fill the screen with 4 x 3 content by "lying" to the set top box in the set up area and saying that you have a 4 x 3 television. That option is not optimal though as you then have to change it back for HDTV programming.