dropped_frames.lua

obs           = obslua
source_name   = ""

last_text     = ""
activated     = false

obs_output    = nil
full_text     = 'Dropped frames: '

-- Function to set the time text
function set_time_text()
	local text          = string.format("%02d", obs.obs_output_get_frames_dropped(obs_output))

	if text ~= last_text then
		local source = obs.obs_get_source_by_name(source_name)
		if source ~= nil then
			local settings = obs.obs_data_create()
			obs.obs_data_set_string(settings, "text", full_text .. text)
			obs.obs_source_update(source, settings)
			obs.obs_data_release(settings)
			obs.obs_source_release(source)
		end
	end

	last_text = text
end

function timer_callback()
	set_time_text()
end

function activate(activating)
	if activated == activating then
		return
	end

	activated = activating

	if activating then
    obs_output = obs.obs_frontend_get_streaming_output()
		set_time_text()
		obs.timer_add(timer_callback, 500)
	else
    obs.obs_output_release(obs_output)
		obs.timer_remove(timer_callback)
	end
end

-- Called when a source is activated/deactivated
function activate_signal(cd, activating)
	local source = obs.calldata_source(cd, "source")
	if source ~= nil then
		local name = obs.obs_source_get_name(source)
		if (name == source_name) then
			activate(activating)
		end
	end
end

function source_activated(cd)
	activate_signal(cd, true)
end

function source_deactivated(cd)
	activate_signal(cd, false)
end

----------------------------------------------------------

-- A function named script_properties defines the properties that the user
-- can change for the entire script module itself
function script_properties()
	local props = obs.obs_properties_create()

	local p = obs.obs_properties_add_list(props, "source", "Text Source", obs.OBS_COMBO_TYPE_EDITABLE, obs.OBS_COMBO_FORMAT_STRING)
	local sources = obs.obs_enum_sources()
	if sources ~= nil then
		for _, source in ipairs(sources) do
			source_id = obs.obs_source_get_id(source)
			if source_id == "text_gdiplus" or source_id == "text_ft2_source" then
				local name = obs.obs_source_get_name(source)
				obs.obs_property_list_add_string(p, name, name)
			end
		end
	end
	obs.source_list_release(sources)

	return props
end

-- A function named script_description returns the description shown to
-- the user
function script_description()
	return "Sets a text source to display the dropped frames.\n\nMade by mkosler"
end

-- A function named script_update will be called when settings are changed
function script_update(settings)
	activate(false)

	source_name = obs.obs_data_get_string(settings, "source")
end

-- a function named script_load will be called on startup
function script_load(settings)
	-- Connect hotkey and activation/deactivation signal callbacks
	--
	-- NOTE: These particular script callbacks do not necessarily have to
	-- be disconnected, as callbacks will automatically destroy themselves
	-- if the script is unloaded.  So there's no real need to manually
	-- disconnect callbacks that are intended to last until the script is
	-- unloaded.
	local sh = obs.obs_get_signal_handler()
	obs.signal_handler_connect(sh, "source_activate", source_activated)
	obs.signal_handler_connect(sh, "source_deactivate", source_deactivated)
end

Works like the example countdown timer. You create a Text Source and then load the script and assign it to that. You might need to toggle the text source visibility once to get it to work. Updates every 0.5 seconds

The naming is funky because I just modified the countdown timer script.