Estou a utilizar o Debian Sid e quero converter um mp3 para mp3, mas
com bitrate inferior. Para isso estou a utilizar o ffmpeg, mas ele não
reconhece o formato mp3.
O comando, com respectivo output, é este:

brunomiguel@lunix:~/Desktop$ ffmpeg -i Koop\ -\ 01\ -\ Koop\ Island\
Blues.mp3 -acodec mp3 -ab 80k Koop-Koop_Island_Blues.mp3
FFmpeg version SVN-rUNKNOWN, Copyright (c) 2000-2007 Fabrice Bellard,
et al.
configuration: --prefix=/usr --libdir=${prefix}/lib --shlibdir=$
{prefix}/lib --incdir=${prefix}/include/ffmpeg --enable-shared --
enable-libmp3lame --enable-gpl --enable-libfaad --mandir=${prefix}/
share/man --enable-libvorbis --enable-pthreads --enable-libfaac --
enable-libxvid --enable-pp --enable-libamr-nb --enable-libamr-wb --
enable-x11grab --enable-libogg --enable-libgsm --enable-libx264 --
enable-liba52 --enable-libtheora --extra-cflags=-Wall -g -fPIC -DPIC --
cc=ccache cc --enable-swscaler
libavutil version: 49.5.0
libavcodec version: 51.42.0
libavformat version: 51.12.2
built on Sep 3 2007 12:26:56, gcc: 4.2.1 (Debian 4.2.1-3)
Input #0, mp3, from 'Koop - 01 - Koop Island Blues.mp3':
Duration: N/A, bitrate: 192 kb/s
Stream #0.0: Audio: mp3, 44100 Hz, stereo, 192 kb/s
Unknown encoder 'mp3'