sharp

# using libfaac on Mac OS X 10.6.8
# -vn : not copying video
# -acodec : specify codec used in flv file
# -ac : channels. 1 is for mono, 2 is for stereo
# -ab : specify bitrate for output file (note that rate is not kbps but bps)
# -ar : sampling frequency (Hz)
# -threads: number of threads for encoding
# "-strict experimental" is necessary to use libfaac

ffmpeg -y -i xxxxxxxxxxx.flv -vn -acodec aac -ac 2 -ab 128000 -ar 44100 -threads 4 -strict experimental xxxxx.m4a