1) convert flv to mp3
facvt xxx.flv -out xxx.mp3 -fmt mp3 -ac 1 -asr 44100 -abr 64000

2) convert flv to wav
facvt xxx.flv -out xxx.wav -fmt wav -ac 1 -asr 44100

3) convert flv to amr
facvt xxx.flv -out xxx.amr -fmt amr -ac 1 -asr 8000 -abr 12000