An Aegisub script to set the background on all selected lines of text to 25% opacity

aegisub-bg-opacity.lua

-- Macro that adds BG transparency tags in front of every selected line

local tr = aegisub.gettext

script_name = tr"Add BG transparency"
script_description = tr"Adds 25% background opacity to the start of all selected lines"
script_author = "Lexi"
script_version = "1"


function add_edgeblur(subtitles, selected_lines, active_line)
	for z, i in ipairs(selected_lines) do
		local l = subtitles[i]
		l.text = "{\\3a&H40&}" .. l.text
		subtitles[i] = l
	end
	aegisub.set_undo_point(script_name)
end

aegisub.register_macro(script_name, tr"Adds BG opacity to all selected lines", add_edgeblur)