ffmpeg -i test.wav ~/Desktop/out.mp3
ffmpeg version N-37650-g3c939ad Copyright (c) 2000-2012 the FFmpeg developers
  built on Feb  8 2012 15:33:28 with gcc 4.4.3
  configuration: --enable-gpl --enable-nonfree --enable-libx264
  libavutil      51. 38.100 / 51. 38.100
  libavcodec     54.  1.100 / 54.  1.100
  libavformat    54.  0.100 / 54.  0.100
  libavdevice    53.  4.100 / 53.  4.100
  libavfilter     2. 62.100 /  2. 62.100
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0.  6.100 /  0.  6.100
  libpostproc    52.  0.100 / 52.  0.100
[wav @ 0x1f113a0] max_analyze_duration 5000000 reached at 5013333
Input #0, wav, from 'test.wav':
  Duration: 00:03:03.98, bitrate: 1536 kb/s
    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, 2 channels, s16, 1536 kb/s
Output #0, mp3, to '/home/user/Desktop/out.mp3':
    Stream #0:0: Audio: none, 48000 Hz, 2 channels, s16, 128 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (pcm_s16le -> ?)
Encoder (codec none) not found for output stream #0:0