I am using a Roku premiere on a Samsung tv. I have the highest tier xfinity package available with nearly every channel. Some of the HBO channels show up like a postage stamp with a black border on all 4 sides. Other channels show up letterbox for some reason instead of going full screen. I have checked the Roku settings and I have tried auto and 1080. They both do the same thing. I have checked in the tv settings and I have tried stretch, 16:9, smart view, and full screen. None of them solve the problem on all channels. My at&t tv app is able to keep all My channels at full screen On an hdd television. It was originally on 16:9 and most had channels are letterbox. What can be done to fix this? For example hbo family is tiny. Yes I am using an HDMI cable and everything is secure. I can use any of the other HD apps and get full screen picture. Xfinity seems to be the only app that is an issue. Roku is up to date, tv is up to date, xfinity stream app is up to date.