The VideoLAN Forums

So how do I configure it so I'd have the max possible quality in the output? (of course I can't outperform the quality of the video itself, but I want it to at least not to worsen it)

This is for encoding, not decoding...

But there would be a difference in quality if I lower some values, right?

not for playback

oh come on, it should mean something, otherwise what's the point in it? So how can I configure it so I will always have the max quality a video can afford?

As j-b said, those settings only have an effect when you encode video (VLC can encode video in case you didn't know).

There really aren't decoding related options that would make huge difference. (you can try post processing filter, but it usually only "helps" when original quality of video is bad)