Aspect Ratio issue on the FireStick 4K
See https://forum.videolan.org/viewtopic.php?f=35&t=148237&p=487988#p487988
https://www.reddit.com/r/fireTV/comments/9ta8xu/vlc_issue_on_fire_tv_stick_4k/
and https://forum.videolan.org/viewtopic.php?f=35&t=147533&p=485826&hilit=stick#p484208
Could be an issue on the hardware decoder or in the UI.