ffmpeg: How to convert FLV to M4A, M4B without losing quality (demux/extract AAC)

How to extract AAC autio tracks from FLV or MP4 video files with freeware command-line ffmpeg (Windows, Linux, Mac OS X)

First of all find out what type of audio is used in the video file:

ffmpeg -i inputfile.flv

You will get something like

Stream #0.1: Audio: AAC, 44100 Hz, stereo, s16, 128 kb/s

Now you know that AAC audio is used (or MP3, or Speex, or Wav,...), so use the following command:

ffmpeg -i input.flv -vn -acodec copy output.m4a

or

ffmpeg -i input.flv -vn -acodec copy output.m4b