click-drag.lua

local state = nil
local o = {
	gap = 20,    -- number of pixels between steps
	step = 1,    -- step factor and precision level
	dBmin = -60, -- silence threshold in decibels
	fmt = '',    -- print format
	x = true,    -- whether to use the x or y axis
}
(require 'mp.options').read_options(o)
local dBmin, dBmax = o.dBmin, 0
local prec = math.abs(o.step)

if o.fmt == '' then
	o.fmt = tostring(o.step)
	local i = o.fmt:find('%.')
	o.fmt = '.'..(i and o.fmt:sub(i + 1):len() or 0)..'f'
end

local k = (mp.get_property('ao') == 'pulse') and 60 or 20

local function drag(_, pos)
	local dif = o.x and (pos.x - state.pos.x) or (state.pos.y - pos.y)
	dif = math.floor(dif / o.gap + 0.5)
	if state.dif ~= dif then
		state.dif = dif
		local dB = math.min(state.dB + (dif * o.step), dBmax)
		local s = (dB <= dBmin and '-∞' or string.format('%+'..o.fmt, dB))..' dB'
		mp.commandv('osd-bar', 'set', 'ao-volume',
			dB <= dBmin and 0 or 10 ^ (2 + dB / k))
		mp.osd_message(string.format('AO-Volume: %s%s', s,
			mp.get_property_bool('ao-mute') and ' (Muted)' or ''), 1)
	end
end

local function click(t)
	if t.event == 'down' then
		local pos = mp.get_property_native('mouse-pos')
		local vol = mp.get_property_number('ao-volume')
		if not (pos and vol) then
			return
		end
		local dB = math.max(dBmin, k * math.log(vol / 100, 10))
		dB = math.floor(dB / prec + 0.5) * prec
		state = { pos=pos, dif=0, dB=dB }
		mp.observe_property('mouse-pos', 'native', drag)
	elseif t.event == 'up' then
		mp.unobserve_property(drag)
	end
end

mp.add_key_binding('MBTN_MID', click, {complex=true})
-- mp.add_key_binding('Ctrl+MBTN_LEFT', click, {complex=true})