optimize performance for 4k

perf-opt-4k.lua

-- optimize performance for 4k
-- on high-res (width > 1920) videos:
--     pre-scale high-res to half the size using lavfi scale filter
--     change deband to no
--     change correct-downscaling to no
-- on normal-res videos:
--     revert everything back

-- from https://github.com/mpv-player/mpv/blob/39e04e929483847a3e0722d86d53f69837ed99db/TOOLS/lua/autocrop.lua
function del_filter_if_present(label)
    -- necessary because mp.command('vf del @label:filter') raises an
    -- error if the filter doesn't exist
    local vfs = mp.get_property_native("vf")
    for i,vf in pairs(vfs) do
        if vf["label"] == label then
            table.remove(vfs, i)
            mp.set_property_native("vf", vfs)
            return true
        end
    end
    return false
end

local filename = ''
local cscale = mp.get_property_native('cscale', 'spline36')
local dscale = mp.get_property_native('dscale', 'mitchell')
local deband = mp.get_property_native('deband', 'no')
local correct_downscaling = mp.get_property_native('correct-downscaling', 'no')

local function optScale4kEventListener()
    if filename == mp.get_property_native('filename') then
--        mp.osd_message("perf-opt-4k: enabled", osd_time)
        return false
    end
    filename = mp.get_property_native('filename')
    local scale = mp.get_property_native("window-scale")
    del_filter_if_present('prescale4k')
    if mp.get_property_number("width") > 1920 then
        mp.command('vf add @prescale4k:lavfi=graph=[scale=w=iw*0.5:h=ih*0.5:flags=bicubic]')
        mp.set_property("cscale", "bicubic_fast")
        mp.set_property("dscale", "bicubic_fast")
        mp.set_property("deband", "no")
        mp.set_property("correct-downscaling", "no")
--        mp.osd_message("perf-opt-4k: enabled", osd_time)
    else
        mp.set_property("cscale", cscale)
        mp.set_property("dscale", dscale)
        mp.set_property("deband", deband)
        mp.set_property("correct-downscaling", correct_downscaling)
--        mp.osd_message("perf-opt-4k: disabled", osd_time)
    end
end

mp.register_event("file-loaded", optScale4kEventListener)