[Haskell-cafe] libmad and os/x coreaudio wrappers

Chris Waterson waterson at maubi.net
Wed Mar 19 14:09:00 EDT 2008

Hi there!  I've taken my first stab at writing some (admittedly
minimal) libraries for Haskell, and would love to get feedback on

   * hmad: a wrapper for the libmad MP3 decoder.

   * CoreAudio: a wrapper for OS/X CoreAudio.

(You should be able to "darcs get" the above links, if you want.)

I wrote the libmad wrapper to generate a "stream" (i.e., a lazy list)
of audio samples.  CoreAudio allows the input stream to be lazy, as
well.  So, here's a simple MP3 player:

 > module Main where
 > import Sound.CoreAudio
 > import Codec.Audio.MP3.Mad
 > import qualified Data.ByteString.Lazy as B
 > import System
 > import System.IO
 > main :: IO ()
 > main = do files <- getArgs
 >           mapM_ playFile files
 > playFile :: String -> IO ()
 > playFile file =
 >     withBinaryFile file ReadMode $ \ inHandle ->
 >        do xs      <- B.hGetContents inHandle
 >           samples <- decode xs
 >           play samples

I do have a couple questions...

   * The CoreAudio library requires its users to be compiled with
     "-threaded".  Is there a way to specify that in the Cabal file?

   * I wanted to be able to generate a variety of streams from libmad.
     Besides stereo linear PCM data, it also seemed like it might be
     worth-while to produce a stream of MP3 frame headers, the
     unsynthesized frequency domain data, and so on.  I tried to
     accomplish this with a the DecoderSink class, but I'm not sure I
     succeeded.  Any thoughts here would be appreciated!

I hope someone else finds these useful.  The FFI was a joy to use once
I figured it out... :)


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