The MKV files (movies) that I edit are always 23.976 FPS.
Will this ever cause a framerate problem when exporting to youtube ?

They are also 1920x800 but with the added horizantal black bars they are said both in the description and on mediainfo to be 1920x1080. If I leave them like that and export them in 1920x1080 then for someone who has a 16/9 screen it will not make a difference but for someone with the perfect wide TV now there will be vertical black bars added and the horizantal (looks like they are fixed. I wonder why they fix them !! I think the movie industry ads thel fixed..) Looks like they always fix them because when I watch any movie trailer on youtube they have the horizontal black bars and when I press on the theater mode (next to full screen) look what happens.. see for yourself.. Now there are both hor. and vert. bars while if the hor. were not fixed the screen would be full..

The only solution is to remove the black bars and then export to 1920x800. I am trying the free version of PD I see there is an option for these but I can't try it with free version. Free only regular resolutions like 1920x1080 are available.

Second thing the few movies I have on mkv are constant frame rate but I read mkv often has variable frame rate.
The music video clips I have are variable frame rate..

Will variable frame rate cause problems like it does on hitfilm ? (I am trying hitfilm too.)
For those interested here is forum question I asked https://fxhome.com/forum/discussion/comment/122966#Comment_122966

3 topics here
23.976FPs
1920x1080 (1920x800 +black bars)
variable frame rate

Any input, whatever it is, is appreciated..