CentOS 7需额外安装扩展源：
su -c 'yum localinstall --nogpgcheck https://download1.rpmfusion.org/free/el/rpmfusion-free-release-7.noarch.rpm https://download1.rpmfusion.org/nonfree/el/rpmfusion-nonfree-release-7.noarch.rpm'
rpm --import http://li.nux.ro/download/nux/RPM-GPG-KEY-nux.ro
rpm -Uvh http://li.nux.ro/download/nux/dextop/el7/x86_64/nux-dextop-release-0-1.el7.nux.noarch.rpm
yum -y install ffmpeg ffmpeg-devel
1.转换amr到mp3：
ffmpeg -i shenhuxi.amr amr2mp3.mp3
2.转换amr到wav：
ffmpeg -acodec libamr_nb -i shenhuxi.amr amr2wav.wav
3.转换mp3到wav：
ffmpeg -i DING.mp3 -f wav test.wav
4.转换wav到amr：
ffmpeg -i test.wav -acodec libamr_nb -ab 12.2k -ar 8000 -ac 1 wav2amr.amr