A WoW AddOn that plays music when you're stealthed and moving.

StealthMusic_Core.lua

-- Declare a local variable called something like IS_PLAYING (we use this a bit later) and set it to false.
-- Create a frame
-- Hide it
-- Register whatever event(s) fire when the player enters/leaves stealth
-- Set its OnEvent script to show the frame when the player enters stealth (allowing its OnUpdate script to run) and hide the frame, stop the music and set IS_PLAYING to false when the player leaves stealth (stopping its OnUpdate script from running).
-- Set its OnUpdate script to check the player's speed every 0.X seconds.
-- 		If the player is moving and IS_PLAYING is false, use PlayMusic to start your music and set IS_PLAYING to true.
-- 		If the player isn't moving and IS_PLAYING is true, use StopMusic to stop the music and set IS_PLAYING to false.
-- http://us.battle.net/wow/en/forum/topic/6412105149#4

local MUSIC_PATH = "Interface\\AddOns\\StealthMusic\\music.mp3"

local IS_PLAYING = false

local function PlayStealthMusic()
	PlayMusic(MUSIC_PATH)
	IS_PLAYING = true
end

local function StopStealthMusic()
	StopMusic()
	IS_PLAYING = false
end

local f = CreateFrame("Frame")
f:Hide()
f:RegisterEvent("UPDATE_STEALTH")

f:SetScript("OnEvent", function(self, event, ...)
	if IsStealthed() then -- We're in stealth, start the OnUpdate script
		self:Show()
	else				  -- We're not in stealth, stop the OnUpdate script and the music.
		self:Hide()
		StopStealthMusic()
	end		
end)

local THROTTLE = 0.1 -- How many seconds to wait before running the OnUpdate
local timer = THROTTLE

f:SetScript("OnUpdate", function(self, elapsed)
	timer = timer - elapsed
	if timer > 0 then return end -- Don't run the code until at least THROTTLE seconds have passed
	
	timer = THROTTLE -- Reset the timer
	
	local speed = GetUnitSpeed("player")
	if speed == 0 and IS_PLAYING then -- We're not moving but the music is still playing, so stop it.
		StopStealthMusic()
	elseif speed > 0 and not IS_PLAYING then -- We're moving but the music isn't playing, so start it.
		PlayStealthMusic()
	end
end)