When the input is 4:3, the 1920x1080 or 3840x2160 format suggestions are not helpful since there is no sense in creating unnecessary black shoulders.
I suggest that the offered automatic sizes adopt to 4:3 ratios when the the input file is 4:3 ratio, so to offer e.g. 1440x1080 and 2880x2160 instead. I haven’t yet seen any hardware that could not play these formats.
I’d suggest not using those fixed “standard” resolutions for odd video sizes or aspect ratios other than 16:9.
Just use the 2x or 4x upscale and then use a player that resizes OTF during playback.
(TVAI just does 2x or 4x upscales and then simply uses a lanzcos filter to get the final res anyways…)
I’ve seen too many 4:3 videos stretched to 16:9 to not put the black bars on. Usually it’s through no fault of the person playing the video. That’s just what the default settings do on the TV or whatever is playing the video do. Sometimes, of course, there is no option to correct it.
