I want to put a video shot in Full HD on a 4K timeline and finally output it as a 4K video. I suspect that the display may be degraded. What precautions should be taken? Also, if there is a way to prevent it from deteriorating, please let me know.
Since it is an integer multiple from 1920 x 1080 to 3840 x 2160, I don't think it will be much of a problem when viewed alone. Of course, if you look side by side, you can see that the resolution is double.
If it is not an integer multiple, for example, it will be necessary to express 1 pixel with 1.5 pixels, so the impression of blurring will be strong. In terms of image, it feels like you were able to display at a resolution other than 1/integer on your display.
Even integer multiples are problematic. When 4K and Full HD videos are mixed in one video, the difference in resolution is noticeable because the resolution changes every time the clip is switched.
As a method to solve this problem, there is super resolution technology Super Scale.
Right-click the material in the media pool and set it for each media with Super Scale on the "Video" tab of "Clip Attributes".
It is explained from around 23:45.
There is also an explanation here.