Choose the VO based on if the laptop is plugged in or not. (OS X)

vo_battery.lua

-- If the laptop is on battery, the VO set in the config will be choosen,
-- else the one defined with „hqvo“ is used.
local hqvo = "opengl-hq:gamma-auto"
local utils = require 'mp.utils'
if mp.get_property_bool("option-info/vo/set-from-commandline") == true then
    return
end
t = {}
t.args = {"/usr/bin/pmset", "-g", "ac"}
res = utils.subprocess(t)
if res.stdout ~= "No adapter attached.\n" then
    mp.set_property("options/vo", hqvo)
end