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extract AAC audio from flv, and convert aac to mp3 using ffmpeg
# 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
# note that codec is 'libmp3lame'
ffmpeg -i xxxxxxxxxx.m4a -vn -acodec libmp3lame -ac 2 -ab 128 -ar 44100 -threads 4 -f mp3 zzzzzzzzzzz.mp3
# or you can directly convert audio track
ffmpeg -i xxxxxxxxxxx.flv -vn -acodec libmp3lame -ac 2 -ab 128000 -ar 44100 -threads 4 -f mp3 xxxxx.mp3
# for wav -acodec option is not necessary
ffmpeg -i xxxxxxxxxx.flv -vn -threads 4 -ac 1 -ar 44100 xxxxxx.wav
# for ogg
ffmpeg -i xxxxxxxxxx.flv -vn -threads 4 -acodec libvorbis -ac 2 -ar 44100 xxxxxxx.ogg
# simply extract audio without transcoding it.
ffmpeg -i xxxxxxxxxx -vn -threads 4 -acodec copy output.filename
# chop mp4 with/without transcoding
ffmpeg -ss <start.second> -i xxxxxx -t <duration.second> output.filename
ffmpeg -ss <start.second> -i xxxxxx -t <duration.second> -acodec copy -vcodec copy output.filename
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