can I convert one of this format to compatible 16000.0 Sample Rate FLAC file?

kAudioFormatLinearPCM                   = 'lpcm',
kAudioFormatAppleIMA4                   = 'ima4',
kAudioFormatMPEG4AAC                    = 'aac ',
kAudioFormatMACE3                       = 'MAC3',
kAudioFormatMACE6                       = 'MAC6',
kAudioFormatULaw                        = 'ulaw',
kAudioFormatALaw                        = 'alaw',
kAudioFormatMPEGLayer1                  = '.mp1',
kAudioFormatMPEGLayer2                  = '.mp2',
kAudioFormatMPEGLayer3                  = '.mp3',
kAudioFormatAppleLossless               = 'alac'

I tried using ffmpeg

ffmpeg -i audio.xxx -acodec flac audio.flac

but result is

FFmpeg version CVS, Copyright (c) 2000-2004 Fabrice Bellard
Mac OSX universal build for ffmpegX
  configuration:  --enable-memalign-hack --enable-mp3lame --enable-gpl --disable-vhook --disable-ffplay --disable-ffserver --enable-a52 --enable-xvid --enable-faac --enable-faad --enable-amr_nb --enable-amr_wb --enable-pthreads --enable-x264 
  libavutil version: 49.0.0
  libavcodec version: 51.9.0
  libavformat version: 50.4.0
  built on Apr 15 2006 04:58:19, gcc: 4.0.1 (Apple Computer, Inc. build 5250)
Input #0, wsaud, from 'audio.alac':
  Duration: 00:00:03.8, start: 0.000000, bitrate: 199 kb/s
  Stream #0.0: Audio: adpcm_ima_ws, 24931 Hz, stereo, 199 kb/s
Unable for find a suitable output format for 'audio.flac'

I also installed flac codec for mac, but nothing...

I tried also use convtoflac.sh (from http://legroom.net/software/convtoflac) but result is similar.

Any idea to convert in flac?