I made a quick installer script that will install MPlayer 1.0rc1 with the essential codecs pack and the Firefox plugin on a new installation of Slackware 12. With this script you should be able to get MPlayer set up on Slackware 12 in 3 easy steps.
1. Download The MPlayer Installer that I made (Right click Save Link As).
2. Change to root user and run the MPlayer Installer OR run the MPlayer Installer with sudo as followed:
bash-3.1$ su root
bash-3.1# sh mplayer_setup.sh
3. If everything installed smoothly you can remove the mplayer directory and all files inside it. If it failed then all you need to do is (as root) removepkg on all of the .tgz files and do a rm /usr/lib/codecs/*.
Firefox should be restarted after the script has run. Test Firefox by going to various media sites, one I like to use is Apple Trailers (Because of the quality and speed). If you could contact me and let me know if the installer worked or failed I would appreciate it.
Line by line breakdown of the installer:
mkdir mplayer; cd mplayer;
Creates the mplayer directory and moves into it.
wget http://www2.linuxpackages.net/packages/Slackware-12.0/X11/MPlayer/mplayer-1.0rc1-i486-1goa.tgz; installpkg mplayer-1.0rc1-i486-1goa.tgz
Gets the mplayer-1.0rc1-i486 package from linuxpackages.net then installs the package
wget http://www2.linuxpackages.net/packages/Slackware-12.0/Library/mplayerplug-in/mplayerplug-in-3.45-i686-1amg.tgz; installpkg mplayerplug-in-3.45-i686-1amg.tgz
Gets the mplayer plug-in for Firefox and installs it
Downloads the essential codecs pack from mplayerhq.hu
tar xvjf essential-20061022.tar.bz2; mv essential-20061022/* /usr/lib/codecs; rm -rf essential-20061022
extracts the essential codecs package to one of the directories MPlayer looks for codecs in and removes the directory.