This happens with the OpenGL (now 'GPU') video output mode, which I think I remember being the default. You can work around it by going to Advanced, MPlayer/mpv tab, and adding --keepaspect to the 'Options', but this causes an even worse bug if you try to scale the window to match the corrected aspect ratio. I used to be able to add rotate=auto to the video filters, but that no longer seems to fix it since I upgraded to Ubuntu 18.04 (technically KDE Neon). Ubuntu 16.04's version was fixed with the...
This happens with the OpenGL (now 'GPU') video output mode, which I think I remember being the default. You can work around it by going to Advanced, MPlayer/mpv tab, and adding --keepaspect to the 'Options', but this causes an even worse bug if you try to scale the window to match the corrected aspect ratio. I used to be able to add rotate=auto to the video filters, but that no longer seems to fix it since I upgraded to Ubuntu 18.04 (technically KDE Neon). Ubuntu 16.04's version was fixed with the...