Unknown encoder 'libmp3lame'

When you try to convert `.mp4` to `.mp3` with ffmpeg as follows:

ffmpeg -i moon_20160905.mp4 -vn -acodec libmp3lame moon_20160905.mp3

you might encounter the following error:

Unknown encoder 'libmp3lame'

Add `--enable-libmp3lame` when configuring ffmpeg as follows:

./configure --disable-yasm --enable-libmp3lame