ffmpeg -i thirtyminutes.flv -acodec libmp3lame -ab 26k output/thirty.mp3
FFmpeg version SVN-r26402, Copyright (c) 2000-2011 the FFmpeg developers
  built on Jan 23 2012 12:27:33 with llvm_gcc 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2335.15.00)
  configuration: --enable-libmp3lame --enable-shared --arch=x86_64
  libavutil     50.36. 0 / 50.36. 0
  libavcore      0.16. 1 /  0.16. 1
  libavcodec    52.108. 0 / 52.108. 0
  libavformat   52.93. 0 / 52.93. 0
  libavdevice   52. 2. 3 / 52. 2. 3
  libavfilter    1.74. 0 /  1.74. 0
  libswscale     0.12. 0 /  0.12. 0
[flv @ 0x7ff85880b000] Could not find codec parameters (Video: [0][0][0][0] / 0x0000)
[flv @ 0x7ff85880b000] Estimating duration from bitrate, this may be inaccurate
Input #0, flv, from 'thirtyminutes.flv':
  Metadata:
    audiocodecid    : 6
    duration        : 2075
    videocodecid    : -1
    canSeekToEnd    : true
  Duration: 00:34:35.04, start: 3.040000, bitrate: N/A
    Stream #0.0: Video: [0][0][0][0] / 0x0000, 1k tbr, 1k tbn, 1k tbc
    Stream #0.1: Audio: nellymoser, 44100 Hz, mono, s16
File 'output/thirty.mp3' already exists. Overwrite ? [y/N] y
Output #0, mp3, to 'output/thirty.mp3':
  Metadata:
    audiocodecid    : 6
    duration        : 2075
    videocodecid    : -1
    canSeekToEnd    : true
    TSSE            : Lavf52.93.0
    Stream #0.0: Audio: libmp3lame, 44100 Hz, mono, s16, 26 kb/s
Stream mapping:
  Stream #0.1 -> #0.0
Press [q] to stop encoding
size=     756kB time=193.46 bitrate=  32.0kbits/s
video:0kB audio:756kB global headers:0kB muxing overhead 0.018091%