Originally Posted by Ilgar
When the old -dumpaudio failed to work for the .mp4 files, I started using the following script to extract their audio; it seems to work for .flv files as well:
mplayer -quiet $1 -ao pcm:fast:file=$2 -vc dummy -vo null -channels 2
Here $1 is the .flv file and $2 is the output filename.
I, too, have been wrestling with this to get an audio track into a video I am doing from a YouTube video. This is the one that finally worked.