Subtitles resizing on window size?

[Gilles]

Hello.
I'm having a little issue. I have 2 screens, one is for the usual stuff and the other is for watching videos/movies.

The problem is that my 1st screen has a resolution of 1920x1080 and the second one is 3840x2160. And when I play the video with subs in the frst screen, they have a normal size but are tiny (almost unreadable) on the second one. And if I resize them manually for an optimal size for the second screen, then of course they are gigantic on my first screen.

So, I want to know how to have it resized depending on the window screen. I know it's possible (I remember having done this in the past, long ago, but can't remember how) but it doesn't seem to work. Not anymore at least.

There's that option in the preferences => font size => "OSD size and automatic font size" / or "activate font size depending on the resolution". But that doesn't work at all. Nothing is resized. I tried it in every aspect.

I tried to test all the options using different video renders modes. Only one worked: the VMR7. However that mode had a crappy image, the lines were distorted... So that won't do it.

Any help welcome.