Thanks for reconfirming. I dug deeper on my side:
a) GUI resolution 1920x1080@50, whitelist 1920x1080@50, 3840x2160@25
Playing the interlaced clip, i see how my projector tries to change display mode, but when i see a picture again, the projector claims 1920x1080@50. But the picture is jumpy.
b) removing the 3840x2160@25 from whitelist fixes the issue. Adding any other whitelist resolutions does not cause any issue, but my projector does not have any other (lower than 4k resolution) @25 display mode, and i guess the problem is with @25 resolutions.
c) Disabling HW acceleration with 3840x2160@25 in the whitelist makes vero4k+ switch to 3840x2160@25 during playback, no jumpyness.
One theory is that there is some incorrect coding in the HW acceleration including changing of display resolution, e.g.: the HW may think it did switch to a framerate of 25Hz during playback but it actually did not.
When i do the same with 1920x1080@60 instead of 1920x1080, the display also seems to want to change resolution, but then shows it has stayed on 1920x1080@60 and playback is now slowed down…
Alas, i do not have another 4k display to see if this is specific to my projector or not, but if a display has 1920x1080@50 and 3840x2160@25 then it should be possible to either reproduce the above whitelist setup and see how it plays back.
There is a bit of GUI diagnostics missing. E.g.: It would be great if the "i"nfo display would also show the screen resolution that the vero4k+ thinks it is using. If that shows different from the one the display shows (as is my theory), that would help.
I don’t think i actually ever need 3840x2160@25, because for european TV UHD (25 fps), 3840x2160@50 should also work (i am not even aware of any UHD with 25 fps), so i think i can work around this issue by just not having 3840x2160@25 in the whitelist, but maybe its interesting for you folks to look what is wrong, in case the issue also affects other whitelist combinations that may be more relevant.
Another side issue i saw was that when HW acceleration is on the in-movie video settings show “Deinterlacing off” and is greyed out (not configurable). Luckily the HW is correctly deinterlacing the videos, but its kinda weird to see a wrong unconfigurable value. If the vero4k doesn’t even let OSMC know if its deinterlacing in HW, then maybe show greyed out “Deinterlacing auto” instead. Of course for diagnostic purposes i’d love to see in 'i’nfo onscreen display whether or not the video is interlaced, but maybe the HW doesn’t provide that info…