Step 1: install
$ sudo yum install epel-release
$ sudo yum localinstall --nogpgcheck https://download1.rpmfusion.org/free/el/rpmfusion-free-release-7.noarch.rpm
$ sudo yum install ffmpeg
$ ffmpeg -version // test if installed successfully
Step 2 examples:
$ ffmpeg -i input.mp4 output.webm
// turn video format
$ ffmpeg -i input.mp3 output.ogg
// turn audio format