How do I decode a string of 8 bit bytes

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#11

Okay so I did this but I’m getting an error

local RunService = game:GetService("RunService")
local HttpService = game:GetService("HttpService")

local byteString = HttpService:GetAsync('')

local char = string.char
local insert = table.insert

function byte_to_float(bin)
    local sig = bin:byte(2) % 0x80 * 0x10000 + bin:byte(3) * 0x100 + bin:byte(4)
    local exp = bin:byte(1) % 0x80 * 2 + math.floor(bin:byte(2) / 0x80) - 0x7F
        if exp == 0x7F then return 0 end
    return math.ldexp(math.ldexp(sig, -23) + 1, exp) * (bin:byte(1) < 0x80 and 1 or -1)
end

local function decode(hex)
    local str = hex:gsub("\\x%x%x", function(digits) return char(tonumber(digits, 16)) end)
    local floats = {}
    
    for i=1,str:len(),4 do
        insert(floats, byte_to_float(str:sub(i, i + 3)))
    end
    
    return floats
end

print(decode(byteString)[1])

output:

 invalid argument #1 to 'char' (number expected, got nil) <-- local str = hex:gsub("\\x%x%x", function(digits) return char(tonumber(digits, 16)) end)
#12

local str = hex:gsub("\\x%x%x", function(digits) return char(tonumber(digits, 16)) end)
Should be
local str = hex:gsub("\\x%x%x", function(digits) return char(tonumber(digits:sub(3), 16)) end)
Which should remove the hex indicator from the start of each match.

Also, it sounds like your best bet would be sending the raw byte data to a file online, then requesting it in Roblox, instead of doing any hexadecimal conversions, as that introduces overhead and unnecessary storage usage.

1 Like
#13

That fixed that part, but there was also an issue of the first line in your byte to float function

attempt to perform arithmetic (add) on number and

image

#15

In regards to the first line, I believe it’d be better to write to the file using the wb (write binary) tag instead of the w (write text) one as you are working with byte data. This’d allow you to skip over the converting process later on.

(Sixteenth line would become: with open('scripts/wav/wav_bytes.txt', 'wb') as f:)

#16

Actually that is a good point, but how would i get the normalized values from here in roblox?
image
Not talking about the question marks I believe that is a rendering issue but with the other characters

#17

Simply use the string.byte function,

local str = "some string data here"
local bytes = {str:byte(1, -1)}

print(table.concat(bytes, "\n"))
#18

Nevermind about the questionmarks, they actually do appear as they are
image

#19

Oh this works. I will mark this as the solution. Thank you very much for the effort.

stack overflow (string slice too long)
here I would just split the string up then right?

#20

Yea, probably into chunks of 1024 would be a reasonable size.

1 Like
#21

How would I do that in roblox considering the entire thing is just full of random characters

#22 
local rep = string.rep
local insert = table.insert

local function split(str, csize)
	local out = {}
	local pattern = "."..rep(".?", csize - 1)
	
	for m in str:gmatch(pattern) do
		insert(out, m)
	end
	
	return out
end

Where str is the input string, and csize is the size of the chunks (1024 for the example number), and it outputs a table of strings with that length.

1 Like
#23

What happens if #bytes % 1024 is not equal to zero? What happens to the remaining bytes?

#24

They just get added as a string at the end, even if it isn’t the full length.

1 Like
#25

Oh also here it says the pattern is too complex

local pattern = "."..string.rep(".?", csize - 1)

for m in str:gmatch(pattern) do
		table.insert(out, m)
	end
#26

Sorry about that, I have written a different formula that might work better:

local insert = table.insert

local function split(str, csize)
	local out = {}
	
	for i=1,str:len(),csize do
	insert(out, str:sub(i, i + csize - 1))
	end
	
	return out
end

print(table.concat(split("test", 3), "\n"))
1 Like
#27

Oh no need to apologize mate, sorry just want more thing.

So now that the bytes are split up, I tried to convert each byte into its value and then normalize it but it will return me only zero

local function split(str, csize)
	local out = {}
	
	for i=1,str:len(),csize do
        local value = str:sub(i, i + csize - 1):byte(1,-1)
        local normalized = (value - 128) / 127.0

	    table.insert(out, normalized)
	end
	
	return out
end

local chunks = split(byteString, 1024)

print(chunks[10])

which is weird because if I did this, it will spit out all the numbers correctly (128,128,128,…)

local function split(str, csize)
	local out = {}
	
	for i=1,str:len(),csize do
	    table.insert(out, str:sub(i, i + csize - 1))
	end
	
	return out
end

local chunks = split(byteString, 1024)

print(chunks[10]:byte(1,-1))
#28

Hopefully this function should cover all your needs:

local insert = table.insert

local function split_and_normalise(str)
	local out = {}
	local csize = 1024
	
	for i=1,str:len(),csize do
		local res = {str:sub(i, i + csize - 1):byte(1, -1)}
		for i=1,#res do
			insert(out, (res[i] - 128) / 127.0)
		end
	end
	
	return out
end

print(table.concat(split_and_normalise("test"), "\n"))
1 Like
#29

Yeah, it still returns zero. Just wondering are you returning an entire string for each chunk?

local function split_and_normalise(str)
	local out = {}
	local csize = 1024
	
	for i=1,str:len(),csize do
		local res = {str:sub(i, i + csize - 1):byte(1, -1)}
		for i=1,#res do
			table.insert(out, (res[i] - 128) / 127.0)
		end
	end
	
	return out
end

local chunks = split_and_normalise(byteString, 1024)

print(chunks[10])
#30

what am i looking at … roblox went from obbys to this?

1 Like
#31

To use it, just enter the string, no need for chunk size this time, and it returns a table of all the normalised values, so no need to index the table.