What happens when someone is watching your 1280x720 video on a 4k or Full HD capable TV? It gets upscaled and still look good, but likely not as good as if you had uploaded at 1920x1080, right?
If you upload @ 1920x1080, then YT will automatically create the lesser resolutions with reduced file sizes, so there really isn’t a huge downside that I can see. Also, you can adjust your CRF (assuming you are using a constant rate factor) to reduce sizes even more, although it may result in quality loss (you will need to experiment with that).
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