**** Update i recommend you install yum priorities plugin to avoid base system files getting replaced. As of this writing the files replaced are alsa based files and causes no system issues, but for some modifying the base system is an issue, so i have tested the whole install again with the priorities plugin and all works as expected. ****
Now just to be clear all this works for both 32-bit and 64-bit Scientific Linux.
Step 1: Add the Atrpms Repo *** for centos pull the proper package.***
32-bit --> rpm -Uhv http://dl.atrpms.net/all/atrpms-repo-6-6.el6.i686.rpm
64-bit --> rpm -Uhv http://dl.atrpms.net/all/atrpms-repo-6-6.el6.x86_64.rpm
yum -y install atrpms-repo
Step 2: Add the Macromedia Repo 32-bit and 64-bit
Adobe has released a yum repo for 64-bit so it has been added. please only choose one of the rpm options below 32/64 has been marked.
32-bit --> rpm -Uhv http://linuxdownload.adobe.com/adobe-release/adobe-release-i386-1.0-1.noarch.rpm
64-bit --> rpm -Uhv http://linuxdownload.adobe.com/adobe-release/adobe-release-x86_64-1.0-1.noarch.rpm
Step 3: Install Multimedia Applications
yum install ffmpeg libdvdcss libdvdread libdvdnav libdvdplay lsdvd libquicktime mplayer mplayerplug-in gstreamer-plugins-ugly gstreamer-ffmpeg gstreamer-plugins-bad-free
Step 4: Install Flash Support
yum install flash-plugin
you should now have full multimedia and video support for all popular formats. If you experience any issue or have a better approach feel free to post a reply I am always listening.