According to the mpv FAQ ~ HERE:
Create a lua-settings/osc.conf text file inside mpv’s configuration directory (that is: ~/.config/mpv/lua-settings/osc.conf) with these lines:
layout=box
seekbarstyle=slider
deadzonesize=0
minmousemove=3
Other options for the on-screen-display - here.
UPDATE regarding newer versions:
~ In relation with this question: What is the location of the settings-file for the MPV on-screen-controller in newer version (2:0.29.1+git11~bionic) and its answer.
In newer versions the location for that file has changed. Save the file as: instead of ~/.config/mpv/lua-settings/osc.conf, it should be ~/.config/mpv/script-opts/osc.conf. Some options are deprecated (e.g. seekbarstyle=slider; change that to bar, diamond or knob). More details at https://mpv.io/manual/master/#config-syntax.
