You download videos from youtube and want to exctract audio of type mp3 and/or wav from them.
Downloaded youtube vidos often contain spaces in their names and all other kind of symbols. If there is batch of videos to convert then use following command in Ubuntu or any other linux (possibly you are missing a few packages that enabke you do this):
for i in *.flv; do ffmpeg -i "$i" -vn -acodec libmp3lame -aq 4 "$i.mp3"; mplayer -vo null -vc dummy -ao pcm:waveheader:file="$i.wav" "$i.mp3"; done
Firstly this script extracts aac audio, converts it to mp3 and then uses created mp3 to create wav also.
There is trick that all $i-s must be enclosed in quotes otherwise spaces mess up the script. One other trick is that if you just want to extract audio then you cannot use “copy” in ffmpeg and use file extension mp3, no player cannot play mp3 that is encoded in aac as youtube does.