ffmpeg external mic

ubuntu@ubuntu:~$ ffmpeg -f oss -i /dev/dsp audio.mp3
ffmpeg version git-2012-01-21-9e53f62 Copyright (c) 2000-2012 the FFmpeg developers
  built on Jan 21 2012 16:14:53 with gcc 4.4.3
  configuration: --enable-gpl --enable-libmp3lame --enable-libvorbis --enable-libxvid --enable-x11grab --enable-libx264 --enable-nonfree --enable-pthreads --enable-libfaac --enable-postproc --enable-libtheora --enable-zlib --enable-version3
  libavutil      51. 34.101 / 51. 34.101
  libavcodec     53. 57.105 / 53. 57.105
  libavformat    53. 30.100 / 53. 30.100
  libavdevice    53.  4.100 / 53.  4.100
  libavfilter     2. 59.101 /  2. 59.101
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0.  6.100 /  0.  6.100
  libpostproc    52.  0.100 / 52.  0.100
[oss @ 0x36283e0] /dev/dsp: Device or resource busy
/dev/dsp: Input/output error