ffmpeg

ffmpeg -i "datei1.flv" -ab 128k -ar 44100Hz -ac 2 "datei2.mp3"

for i in *.flv; do ffmpeg -i "$i" -ac 2 -ar 44100Hz -ab 128k "$i.mp3"; done 

ffmpeg -i VideoFile.flv -ss 00:00:01.00 -vcodec mjpeg -vframes 1 -f image2 VideoFile.jpg