Many SD channels incorrectly encoded - XFinity

This question is about "Many SD channels incorrectly encoded", with XFinity-Comcast TV channels, programming, and sports. On my 16:9 HDTV most SD channels are stretched by 4/3, regardless of the channel's aspect ratio. That means 4:3 channels covers the entire screen and 16:9 channels have black stripes above and below.

I tried playing with different options in the cablebox's setup menu, but the only thing that can change the result is "auto pillarbox". With that option on, 4:3 channels are pillarboxed with black stripes left and right, but 16:9 channels now have black stripes on all four sides.

There are just a couple of 16:9 channels that covers the entire screen, regardless of the settings of "auto pillarbox". They include KTFS, KRON and KCSMJ.

Strangely, Live TV channels from, when shown on my laptop, have the same effect. Stretched 16:9 channels have black stripes all around, and KRON looks fine.

This lead me to wonder whether most SD channels are incorrectly encoded: the program is in 16:9, but is letterboxed to 4:3 and then broadcasted. For example, Live TV from is 16:9, but the same channel (KTVU) is shown with black stripes all around in

Hope I explained everything and this can be fixed.

This topic covered Many SD channels incorrectly encoded, and XFinity - Comcast cable tv service.