-- This script enables live control of the dynamic range compression
-- (drc) audio filter while the video is playing back. This can be
-- useful to avoid having to stop and restart mpv to adjust filter
-- parameters. See the entry for "drc" under the "AUDIO FILTERS"
-- section of the man page for a complete description of the filter.
--
-- This script registers the key-binding "\" to toggle the filter between 
--
-- * off
-- * method=1 (single-sample smoothing)
-- * method=2 (multi-sample smoothing)
--
-- It registers the keybindings ctrl+9/ctrl+0 to decrease/increase the
-- target ampltiude. These keys will insert the filter at the default
-- target amplitude of 0.25 if it was not previously present.
--
-- OSD feedback of the current filter state is displayed on pressing
-- each bound key.

script_name=mp.get_script_name():gsub("lua/","",1)

function print_state(params)
    if params then
	mp.osd_message(script_name..':\n'
			   .."method = "..params['method'].."\n"
			   .."target = "..params['target'])
    else
	mp.osd_message(script_name..':\noff')
    end
end

function get_index_of_drc(afs)
    for i,af in pairs(afs) do
	if af['label']==script_name then
	    return i
	end
    end
end

function append_drc(afs)
    afs[#afs+1]={
	name="drc",
	label=script_name,
	params={
	    method="1",
	    target="0.25"
	}
    }
    print_state(afs[#afs]['params'])
end

function modify_or_create_af(fun)
    afs=mp.get_property_native('af')
    i=get_index_of_drc(afs)
    if not i then
	append_drc(afs)
    else
	fun(afs,i)
    end
    mp.set_property_native('af',afs)
end

function drc_toggle_method_handler()
    modify_or_create_af(
	function (afs,i)
	    new_method=(afs[i]['params']['method']+1)%3
	    if new_method==0 then
		table.remove(afs,i)
		print_state(nil)
	    else
		afs[i]['params']['method']=tostring((afs[i]['params']['method'])%2+1)
		print_state(afs[i]['params'])
	    end
	end
    )
end

function drc_scale_target(factor)
    modify_or_create_af(
	function (afs)
	    afs[i]['params']['target']=tostring(afs[i]['params']['target']*factor)
	    print_state(afs[i]['params'])
	end
    )
end

function drc_louder_handler()
    drc_scale_target(2.0)
end

function drc_quieter_handler()
    drc_scale_target(0.5)
end

-- toggle between off, method 1 and method 2 
mp.add_key_binding("\\","drc_toggle_method",drc_toggle_method_handler)
-- increase or decrease target volume
mp.add_key_binding("ctrl+9","drc_quieter",drc_quieter_handler)
mp.add_key_binding("ctrl+0","drc_louder",drc_louder_handler)