I have a service with HD. STB was set to 1080p out. (I also tried 720p out.)
The STB glitched on Saturday, so I had to call for a refresh to restore it.
After that, I noticed that soem of the SD channels displayed as expected, with a 4:3 aspect rato. (Filled the 16:9 screen vertically, with black bars on the sides.) Most of the SD channels displayed a 16:9 image that didn't fill the screen (Black bars on all 4 sides.) After spending a hour with two levels of Comcast support yesterday, I gave up and swapped the STB. The problem persists. If I set the display zoom function to "full", the 16:9 images are stretched horizontally to fill the screen, and are distorted.
I looked more closely. The SD channels that displayed at 16:9 really are16:9 content. I can zoom using the TV to approximately fill the screen.
Is this a bug or a feature?
A lot of the times this ends up being an issue with the souce video being reformatted too many times. Most broadcasters simply reformat the 16:9 HD feeds and letterbox them into a 4:3 format. I've noticed for whatever reason that on some channels they are getting formatted a second time causing the bars all the way around. Is this on an X1 box or an older style cable box? If it is on X1 I would say just enable the auto-tune HD feature to bypass the SDs entirely as there are very few that aren't available in HD.
It's an X1 box.
The auto-tune HD feature is active. I almost entirely watch HD channels, with rare exceptions. There are many SD-only channels, though.
I thought that what I'm seeing must be exactly that: a 16:9 image letterboxed into 4:3, which is not rescaled to fill the screen. Not ideal.
It may be that things have been like this for a long time, and that I had a false impression due to just landing on a 4:3 channel when testing in the past.
Comcast Support seems tro be clueless about this, unfortunately.