of cos it's impossible.

It's just like image. If your source image is in .gif format and in very low resolution. Can you make make that image to look better? Maybe can improve it by applying some filter to reduce the noise or sth like that but it only tiny improvement. Overall, it's still worse like before

Same thing apply to video. Improve the video by applying some filters and so on, but remember, it's a tiny bit of improvement. If your source video is so darn crappy, don't even think about turning that crappy into a superb-high-definition video