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

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