DFPWM Converter

--No credit here. It's a CC idiom.
local function yield()
  os.queueEvent("fake")
  os.pullEvent("fake")
end
--From the lua guide.
function newStack ()
 return {""}   -- starts with an empty string
end

function addString (stack, s)
 table.insert(stack, s)    -- push 's' into the the stack
 for i=table.getn(stack)-1, 1, -1 do
  if string.len(stack[i]) > string.len(stack[i+1]) then
   break
  end
  stack[i] = stack[i] .. table.remove(stack)
 end
end
--Credit for the following code should go to: Youka on Github. Ported from io to fs by me.

local function collect_audio_data(filename)
 local seekpos=1
 -- WAVE data storage
 local wav = {channels = nil, sample_rate = nil, samples = nil, data = nil}
 -- Open file
 local file = fs.open(filename, "rb")
 --Damn whoever decided rb shouldn't have a readAll().
 local s=newStack()
 while true do
  local r = file.read()
  if r==nil then break end
  addString(s,r)
 end
 local filecontents = table.concat(s)
 if not file then
  return string.format("Filename %q isn't valid!", filename)
 end
 local seek = function(number)--only has cur mode
  seekpos=seekpos+number
 end
 local read = function(number)--number should be format, but this code only uses number so ill only implement that.
  local ret = string.sub(filecontents,seekpos,(seekpos+number)-1);
  seek(number)
 end
 -- File chunk
 if read(4) ~= "RIFF" then
  return "Isn't a 'RIFF' file"
 end
 seekpos=seekpos+4 -- Ignore file size
 if read(4) ~= "WAVE" then
  return "Isn't a 'WAVE' file"
 end
 -- Subchunks
 while true do
  yield()
  -- Chunk id and size
  local id = read(4)
  local size = read(4)
  -- No more chunks
  if not size then
   break
  -- Chunk to read
  else
   size = bton(size)
   -- Format chunk
   if id == "fmt " then
    local bytes = read(2)
    if not bytes or bton(bytes) ~= 1 then
     return "Data format must be PCM!"
    end
    bytes = read(2)
    if not bytes then
     return "Channels are missing!"
    end
    wav.channels = bton(bytes)
    bytes = read(4)
    if not bytes then
     return "Sample rate is missing!"
    end
    wav.sample_rate = bton(bytes)
    seek(4+2) -- Ignore byte rate and block align
    bytes = read(2)
    if not bytes or bton(bytes) ~= 16 then
     return "Bits per sample must be 16!"
    end
    seek(size-16) -- Ignore extra data
   -- Data chunk
   elseif id == "data" then
    if not wav.channels then
     return "Format must be before data!"
    end
    wav.samples = size / (wav.channels * 2)
    do
     local file_cur_pos = seekpos
     local file_end_pos = #filecontents
     if file_end_pos - file_cur_pos < wav.samples * wav.channels * 2 then
      return "Remaining file bytes aren't enough to collect all samples!"
     end
    end
    wav.data = {}
    for c = 1, wav.channels do
     wav.data[c] = {n = 0}
    end
    for s = 1, wav.samples do
     if (s% 100000)==0 then yield() end
     for c = 1, wav.channels do
      local sample = bton(read(2))
      wav.data[c].n = wav.data[c].n + 1
      wav.data[c][wav.data[c].n] = sample > 32767 and sample - 65536 or sample
     end
    end
    break -- Was last needed chunk
   -- Ignorable chunk
   else
    seek(size)
   end
  end
 end
 -- All WAVE data collected?
 if not wav.channels then
  return "Format is missing!"
 elseif not wav.data then
  return "Data are missing!"
 end
 -- Return no error and WAVE data
 return nil, wav
end
--This code was originally by the author of lionray in java, it has been ported to computercraft by me.
local function newConverter()
 local respinc=7
 local respdec=20
 local lpfstrength=100
 local resp=0
 local level=0
 local lastbit=false
 local flastlevel=0
 local lpflevel=0;
 local myself= {
  ctx_update=function(curbit)
   local target= curbit and 127 or -128
   local nlevel=(level+math.floor((response*(target-level)+128)/256))
   if nlevel==level and level~=target then
    nlevel=nlevel+(curbit and 1 or -1)
   end
   local rtarget=nil
   local rdelta=nil
   rtarget=(curbit==lastbit) and 255 or 0
   rdelta=(curbit==lastbit) and respinc or respdec
    local nresponse=response+math.floor((rdelta*(rtarget-response)+128)/256)
   if nresponse == response and response~=rtarget then
    nresponse=nresponse+((curbit==lastbit) and 1 or -1)
   end
    response=nresponse
   lastbit=curbit
   level=nlevel
  end,
  --No need for decompress, one-way converter (tldr, im lazy)
  compress=function(dest,src,destoffs,srcoffs,len)
   for i=1,len do
    local d = 0;
    for j=1,8 do
     local inlevel = src[srcoffs]
     srcoffs=srcoffs+1
     local curbit = (inlevel>level or (inlevel==level and level==127))
     d=(curbit and ((d/2)+128) or (d/2))
     myself.ctx_update(curbit)
    end
    dest[destoffs]=d
    destoffs=destoffs+1
   end
  end
 }
 return myself
end
----This part, surrounded by 8 dashes, interfaces between the top code and the bottom code.
local function newAudioReader(wav,verboseout,isleft)
 if verboseout then verboseout.say("Converting wav data to wav samples...") end
 errorstr,wavdata=collect_audio_data(wav)
 if errorstr then
  error("Error! "..errorstr)
 end
 for c=1,2 do
  wavdata.data[c].n=nil
  newarray={}
  for i=1,#wavdata.data[c] do
   newarray[math.floor(((32768/wavdata.sample_rate)*(i-1))+1)]=math.floor(wavdata.data[c][i]/256)
   if i% 100000==0 then sleep(0.1) end
  end
  wavdata.data[c]=newarray
 end
 local index = 1
 return {
  read=function(buffertable)
   local remaining=#wavdata.data[isleft and 1 or 2].n-(index-1)
   if(not (#buffertable>remaining)) then
    local bi=1
    while true do
     buffertable[bi]=wavdata.data[isleft and 1 or 2][i]
     bi=bi+1
     index=index+1
    end
   end
   return bytesread
  end
 }
end
----
function convert(wav,out,isleft,verboseout)
 local sampleRate=32768
 --encoded samples are in litte startian
 local newArray=function(length)
  local ret = {}
  for i=1,length do
   table.insert(ret,0)
  end
  return ret
 end
 local readBuffer = newArray(1024)
 local outBuffer = newArray(1024/8)
 local c = newConverter()
 local audioin=newAudioReader(wav,verboseout,isleft)
 local fout = fs.open(out,"wb")
 if verboseout then verboseout.say("Converting wav samples to DFPWM...") end
 while true do
  local read = audioin.read(readBuffer)
  local i =0
  if read < 0 then break end
  c.compress(outBuffer,readBuffer,0,0,read/8)
  fout.write(outBuffer)
  if i%100==0 then yield() end
  i=i+1
 end
 fout.flush()
 fout.close()
end
--CC program to use the api above. Remove this section and loadapi to use as an api.
print("Type the location of the wav file: ")
local wavfileloc=read()
print("Type a location for the DFPWM file to be written to.")
local dfpwmout=read()
print("Use left or right channel? Type just \"2\" for right and any other character for left.")
local chan=read()
chan=(chan~="2")
convert(wavfileloc,dfpwmout,chan,{say=function(s) print(s) end})