While installing FFMPEG supporting packages in your system and get an the following error,

# ruby setup.rb config

setup.rb:283: warning: duplicated key at line 284 ignored: "bin-dir"
setup.rb:788:in `load_rbconfig': uninitialized constant Config (NameError)
    from setup.rb:768:in `invoke'
    from setup.rb:1578:in `<main>'

You need to install ruby package properly and check the support version.
# yum install ruby

or just refer the link to install RUBY.