Series s fuzzy/grainy on video playback apps

Hi there Nick welcome to the community forum! Christopher here, an Xbox fan just like you and has been on Xbox for years already. I would really love to make your day by helping you out. There might be a software issue! Let's try this:

The first step in resetting an Xbox is to open the main menu. This can be accomplished in one of two ways:

Press the home button on your Xbox controller. This is the illuminated button with a stylized X that is centrally located on the front of the controller near the top.

Alternately, you can press the left bumper until you reach the home tab, and then press left on the d-pad.

Press down on the d-pad until you reach the gear icon.

Press the A button to select the gear icon.

With all settings highlighted, press the A button again to open the settings menu.

Press down on the d-pad until you reach System.

Press the A button to open the ​System submenu.

With console info highlighted, press the A button again.

Press down on the d-pad to select reset console.

Press the A button to select this option and move to the final step.

Press left on the d-pad to select Reset and keep my games & apps. Then press the A button. This is the less thorough of the two options, as it only resets the Xbox firmware and settings without touching your games and apps. Try this first, as it allows you to avoid downloading everything all over again.

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I have everything set up I think how it should be, I have the series s set at 4K UHD

Check that HDCP is active in settings, you may be being limited to 480p

I don’t see how this has anything to do with it?

If it's any incorrect/corrupted settings, this will reset the settings.