If you may get an error while install/configure ffmpeg packages 

# ./configure

yasm/nasm not found or too old. Use --disable-yasm for a crippled build.

If you think configure made a mistake, make sure you are using the latest
version from Git.  If the latest version fails, report the problem to the
ffmpeg-user@ffmpeg.org mailing list or IRC #ffmpeg on irc.freenode.net.
Include the log file "config.log" produced by configure as this will help
solve the problem.

You need to install yasm on your system by yum command,
#yum install yasm