ffmpeg -i filename.mp4 filename.mp3
fixed bit rate :
ffmpeg -i video.mp4 -b:a 192K -vn music.mp3
variable bit rate :
ffmpeg -i in.mp4 -q:a 0 -map a out.mp3
variable bit rate of 165 with libmp3lame encoder :
ffmpeg -vn -sn -dn -i input.mp4 -codec:a libmp3lame -qscale:a 4 output.mp3
- -vn disables all video-streams from the input
- -sn disables all subtitle-streams from the input
- -dn disables all data-streams from the input
- -i specifies the input file
- -codec:a libmp3lame specifies the encoder
- -qscale:a 4 specifies the quality target for libmp3lame
- The last argument is the output-file. Note that the file-extension might be used to infer additional information.
References
https://superuser.com/questions/332347/how-can-i-convert-mp4-video-to-mp3-audio-with-ffmpeg
https://superuser.com/questions/1463710/convert-mp4-to-mp3-with-ffmpeg