Can't convert FLAC to MP3 with FFmpeg

Question

How can I convert FLAC to MP3 using FFmpeg?

What I've tried:

ffmpeg -i "file.flac"  "file.mp3"

Stream mapping:
  Stream #0:0 -> #0:0 (flac -> ?)
Encoder (codec none) not found for output stream #0:0

file.mp3 is empty


ffmpeg -codecs | grep flac
ffmpeg version N-46093-g14f69a0 Copyright (c) 2000-2012 the FFmpeg developers
  built on Oct 28 2012 15:24:03 with gcc 4.4.6 (GCC) 20120305 (Red Hat 4.4.6-4)
  configuration: --enable-libvpx --enable-libx264 --enable-libxavs --enable-libxvid --enable-pic --enable-thumb --enable-libfaac --enable-gpl --enable-nonfree
  libavutil      52.  1.100 / 52.  1.100
  libavcodec     54. 69.100 / 54. 69.100
  libavformat    54. 35.100 / 54. 35.100
  libavdevice    54.  3.100 / 54.  3.100
  libavfilter     3. 20.106 /  3. 20.106
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 16.100 /  0. 16.100
  libpostproc    52.  1.100 / 52.  1.100
 DEA..S flac                 FLAC (Free Lossless Audio Codec)


ffmpeg -codecs | grep mp3
ffmpeg version N-46093-g14f69a0 Copyright (c) 2000-2012 the FFmpeg developers
  built on Oct 28 2012 15:24:03 with gcc 4.4.6 (GCC) 20120305 (Red Hat 4.4.6-4)
  configuration: --enable-libvpx --enable-libx264 --enable-libxavs --enable-libxvid --enable-pic --enable-thumb --enable-libfaac --enable-gpl --enable-nonfree
  libavutil      52.  1.100 / 52.  1.100
  libavcodec     54. 69.100 / 54. 69.100
  libavformat    54. 35.100 / 54. 35.100
  libavdevice    54.  3.100 / 54.  3.100
  libavfilter     3. 20.106 /  3. 20.106
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 16.100 /  0. 16.100
  libpostproc    52.  1.100 / 52.  1.100
 D.A.L. mp3                  MP3 (MPEG audio layer 3) (decoders: mp3 mp3float )
 D.A.L. mp3adu               ADU (Application Data Unit) MP3 (MPEG audio layer 3) (decoders: mp3adu mp3adufloat )
 D.A.L. mp3on4               MP3onMP4 (decoders: mp3on4 mp3on4float )

Answer 1

Your version of FFmpeg has no MP3 encoder. It can only decode, as indicated by the "D" in the command line output.

If you built it yourself, install LAME before — this depends on your distribution — and then reconfigure it --with-libmp3lame.

Or pick a static build from the FFmpeg download page.

This should give you access to the de facto standard MP3 encoder.