首先yum install yum-priorities，yum-priorities插件可以为yum的源仓库指定优先级.

如果安装包是用高优先级的源仓库安装的，那么这些包就不能用低优先级别的源仓库去更新。同样的，如果一个包可以从多个源仓库中下载安装，但指定了优先级别 之后，这个包就会从最高优先级的源仓库安装。假如用户使用一个或者多个第三方源仓库，这些源仓库都会更新系统文件，有些更新甚至会潜在的危害你的的 CentOS系统，这个时候，该插件就特别起作用了。
现在开始编辑 /etc/yum/pluginconf.d/priorities.conf文件，必须先确认其中有以下的设置：[main]
enabled=1  
然后编辑 /etc/yum.repos.d/，如下：
# CentOS-Base.repo
#
# This file uses a new mirrorlist system developed by Lance Davis for CentOS.
# The mirror system uses the connecting IP address of the client and the
# update status of each mirror to pick mirrors that are updated to and
# geographically close to the client. You should use this for CentOS updates
# unless you are manually picking other mirrors.
#
# If the mirrorlist= does not work for you, as a fall back you can try the
# remarked out baseurl= line instead.
#
#
[base]
name=CentOS-$releasever – Base
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
#baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
priority=1
#released updates
[updates]
name=CentOS-$releasever – Updates
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
#baseurl=http://mirror.centos.org/centos/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
priority=1
#packages used/produced in the build but not released
[addons]
name=CentOS-$releasever – Addons
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=addons
#baseurl=http://mirror.centos.org/centos/$releasever/addons/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
priority=1
#additional packages that may be useful
[extras]
name=CentOS-$releasever – Extras
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
#baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
priority=1
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever – Plus
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
#baseurl=http://mirror.centos.org/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
priority=2
也就是每个仓库后面添加了个priority=x，通过上面的设定之后，Yum将不会从低优先级的源更新那些来自base和update仓库的的安装包。
这 里x必须取1到99之间的整数。仓库的默认优先级是99.序号最小的源仓库具有最高的优先级。同常，最好是为CentOS base 和 update仓库选择非常高的优先级（毕竟是官方的嘛！），在上面的CentOS-Base.repo 文件里，CentOS base 和 update仓库都被指定了最高的优先级（priority=1）。
下面开始安装mplayer：
安装RPMforge：
先下载rpmforge-release包，根据你的系统，从下面的链接中选择一个下载。
i386http://apt.sw.be/redhat/el5/en/i386/RPMS.dag/rpmforge-release-0.3.6-1.el5.rf.i386.rpm
x86_64 http://apt.sw.be/redhat/el5/en/x86_64/RPMS.dag/rpmforge-release-0.3.6-1.el5.rf.x86_64.rpm
安装DAG’s GPG key
#rpm –import http://dag.wieers.com/rpm/packages/RPM-GPG-KEY.dag.txt
检查你下载的包
#rpm -K rpmforge-release-0.3.6-1.el5.rf.*.rpm
安装rpmforge包
#rpm -i rpmforge-release-0.3.6-1.el5.rf.*.rpm
运行了上述的命令后，将会向yum源仓库里加入一个配置文件，并且会导入合适的 GPG keys。此时，最好也设置RPMForge仓库的优先级。
用下面的命令检查更新
#yum check-update
最后就安装mplayer了
#yum install mplayer*
然后到这里下载两个编码包all-20071007.tar.bz2和windows-all-20071007.zip
http://www1.mplayerhq.hu/MPlayer/releases/codecs/
yum安装mplayer后编码包默认应安装在/usr/lib/codecs/中，
# tar jxvf all-20071007.tar.bz2
# mv -f all-20071007/* /usr/lib/codecs/
# unzip windows-all-20071007.zip
# mkdir /usr/lib/win32
# mv window-all-20071007/* /usr/lib/win32
# ln -s /usr/lib/codecs /usr/lib/win32
再看看应用程序的影音中是不是出现了mplayer？启动mplayer就可以播放了，rmvb也一样搞定