You can easily extract audio from video files such as avi, mpg, even flv! into mp3 uses either mplayer or ffmpeg. You can even record online stream into mp3, such as stream from radio cast.
Lets begin with mplayer. To extract audio from video files, use -dumpaudio option and specified the output filename with -dumpfile
mplayer -dumpaudio nodame_theme.flv -dumpfile nodame_theme.mp3
Okay check out the output:
MPEG ADTS, layer III, v2, 8 kBits, 22.05 kHz, Monaural
Okay, The audio extracted from flv, so quality is quite low, haha. But you can change the audio rate by using ffmpeg. Let see how to use ffmpeg.
ffmpeg -i nodame_theme.flv -ab 128 -ar 44100 nodame_theme.mp3
-i is to specified input file, -ab audio bitrate, -ar audio sampling frequency
Let say what file tells you.
MPEG ADTS, layer II, v1, 128 kBits, 44.1 kHz, Monaural
How about record online stream?
First, find an online radio cast to try, you can have plenty of it from shoutcast.
mplayer -dumpstream http://188.8.131.52:80/stream/1005 -dumpfile smoothjazz.mp3
ffmpeg -i http://184.108.40.206:80/stream/1005 -ab 128 -ar 44100 smoothjazz.mp3
Thanks to Mohd Shakir, you can make it a script for stream recording.