I'm watching it in Fullscreen on my 34-inch ultrawide screen monitor without any problems of black bars. However, when I look at the same video from my 1280x800 screen laptop or from my Iphone the bars are present. Some who have viewed my uploaded content have complained as well. I'm not sure what material I would be missing. I record and watch my games in my native 3440x1440 resolution. Only other option I see is to convert what I have to a different resolution for Youtube, though that may reduce the quality of my videos which are 4K.
Ok wait a minute...Do you mean seen the black bars in full screen ?
If so, you have to understand that 3440x1440 is not a regular format, it's more an ultra wide format. Many devices has a 16/9 aspect ratio and yours is not. If I look your video from Youtube in full screen on my 16/9, I can't avoid having black bars. Pretty logical isn't it ? You have no choice to set up as sequence in a 16/9 ratio like a UHD format ( 4K 16/9 in 3840x2160 ) or a classical 1920x1080 (to avoid scaling and loose to much details), to fit most classical devices with a 16/9 ratio and no choice to crop your video if you want it to be full screen with no black bars at all.
One more thing, scaling down a 4k file to 1920x1080 won't decrease the quality of your footage that much when viewing it on a full HD screen. Upscaling a file will result visible quality reduction if you go after 110 % scaling since the pixels get bigger.
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