Photo orientation

All my videos in Photo play in vertically orientation. How to adjust player to play video horizontally?

Personal Videos should be in an “Other Videos” library. Photo libraries should only contain photos. This will allow your videos to play in landscape orientation (if filmed that way)

Just as you suggested, the videos were put in a “Video” library, but since most videos were filmed in a “nomal” portait orientation, it is very hard to view them. Is there a way to tilt them 90 degree?

PLEX cannot rotate your videos (to my knowledge), however HandBreak can: (https://handbrake.fr/). It comes with help files, but in short you add your video, choose your quality settings and on the dimensions tab - select Rotation which can rotate to your desired orientation. Once encoded by HandBreak the new files can be added to your library and be viewed in the correct orientation.