应该是由于没有安装w32codecs的问题，但是Ubuntu的source里又装不了，搜到solution如下。
现在播放DVD都没有问题了，不过我的1区正版魔戒播不了，而在Windows下的SMplayer是可以的，郁闷。
 
This package is not available from the Ubuntu repositories due to licensing and legal restrictions.To play encrypted DVDs, the libdvdcss2 package is essential.

For Ubuntu 9.04 (Jaunty) Users use the following procedures

sudo wget http://www.medibuntu.org/sources.list.d/jaunty.list --output-document=/etc/apt/sources.list.d/medibuntu.list

Then, add the GPG Key using the following commands

sudo apt-get update

sudo apt-get install medibuntu-keyring

sudo apt-get update

For i386 Users install Codecs using the following command

sudo apt-get install w32codecs libdvdcss2

For amd64 Users install Codecs using the following command

sudo apt-get install w64codecs libdvdcss2