When I run mpv with the flag
--fullscreen in my window manager i3, the client sometimes spawns on the wrong monitor. The reason for this behaviour is due to the fact that i3 doesn’t support the EMMH hint called “_NET_WM_FULLSCREEN_MONITORS”, which is something you can read more about on their issue tracker here.
But as a workaround for this issue I created a rule for mpv in i3 that only gets called when I run mpv with the flag
for_window [title="mpvFullscreen"] border none, floating toggle, move window to position 3840 0, resize set 1920 1080
The rule makes mpv float, removes the decoration, moves it to the upper left corner of my third monitor and then rezies it to the same size as my monitor. It’s a fake but instant and flawless looking fullscreen and I’m really happy with it.