Reorder WAV chunks

wav_reorder.lua

-- Reorder WAV chunks files
-- This often useful if particular program expects "WAVE" identifier
-- followed by "fmt " chunk and followed by "data " chunk. Particularly
-- GTA San Andreas User Tracks.
-- You can use part or all of this code without my permissions.

local arg = {...}
local fin = assert(io.open(assert(arg[1], "need input file"), "rb"))
local fout = assert(io.open(assert(arg[2], "need output file"), "wb"))

assert(fin:read(3) == "RIF", "Not RIFF")
local last = fin:read(1)
local big = last == "X"
assert(last == "X" or last == "F", "Not RIFF")
fin:read(4) -- ignore length, recompute later
assert(fin:read(4) == "WAVE", "Not WAVE")

local function string2dword(s, big)
	local a, b, c, d = s:byte(1, 4)

	if big then
		return a * 16777216 + b * 65536 + c * 256 + d
	else
		return d * 16777216 + c * 65536 + b * 256 + a
	end
end

local function dword2string(n, big)
	n = n % 4294967296
	local a = n % 256
	local b = math.floor(n / 256) % 256
	local c = math.floor(n / 65536) % 256
	local d = math.floor(n / 16777216)

	if big then
		return string.char(d, c, b, a)
	else
		return string.char(a, b, c, d)
	end
end

-- We store chunks in memory for sake of simplicity
local chunks = {}

while true do
	io.write("position ", fin:seek("cur"), "\n")
	local fourcc = fin:read(4)
	if not(fourcc) then
		break -- ok EOF
	elseif #fourcc < 4 then
		io.write("Ignoring data at ", fin:seek("cur") - #fourcc, "\n")
		break
	end

	local length = fin:read(4)
	if not(length) or #length < 4 then
		io.write("Ignoring fourcc ", fourcc, " at ", fin:seek("cur") - #length, "\n")
		break
	end
	length = string2dword(length, big)

	io.write(fourcc, " size of ", length, "\n")

	local chunk = fin:read(length)
	if not(chunk) or #chunk < length then
		io.write("Ignoring fourcc ", fourcc, " at ", fin:seek("cur") - #chunk, ". Expected ", length, ", got ", #chunk, "\n")
		break
	end

	chunks[#chunks + 1] = {
		name = fourcc,
		data = chunk
	}
end

fin:close()

-- Reorder "fmt " chunk
local hasfmt = false

for i, v in ipairs(chunks) do
	if v.name == "fmt " then
		table.insert(chunks, 1, table.remove(chunks, i))
		hasfmt = true
		break
	end
end

assert(hasfmt, "missing \"fmt \" chunk")

-- Reorder "data" chunk
local hasdata = false

for i, v in ipairs(chunks) do
	if v.name == "data" then
		table.insert(chunks, 2, table.remove(chunks, i))
		hasdata = true
		break
	end
end

assert(hasdata, "missing \"data\" chunk")

-- Rewrite wav file
local length = 4 -- "WAVE"

for _, v in ipairs(chunks) do
	length = length + #v.data + 8 -- 4cc + length + data
end

-- Write header
fout:write("RIF", last, dword2string(length, big), "WAVE")

for _, v in ipairs(chunks) do
	fout:write(v.name, dword2string(#v.data, big), v.data)
end

fout:close()