HI Gnener, welcome to the community!
I’ve removed the solution marker on your last message for now. The reason is that 4K video should be supported on your QMR (SSSP 6). 4K video support was added with a firmware that I suspect is later than the one you are using. Only 4K videos are supported, 4K images are not.
You are also correct that the resolution of the player is set to 1920x1080. That is the maximum resolution the displays allow applications to run at, but this does not apply to 4K video.
I’m going to send you a private message that includes a firmware I want you to install and a layout that contains a 4K video. I have tested the firmware and video on my QBR (also SSSP 6) and it displays without issue.
Can you report back if the firmware resolves your issue and the video appears on your player? Please note I’m using player version R306.
Many Thanks.