If you want to play protected CDs or DVDs on Arch Linux or any other distro, you may need to install libdvdcss, in order to avoid the message “Media stream scrambled/encrypted”.

In Arch just enter this at the prompt.

sudo pacman -S libdvdcss

You may also need to install libdvdread libdvdnav, so enter at the shell prompt

sudo pacman -S libdvdread libdvdnav

Now you should be able to play those protected CDs, be sure to have legal copy of any copyrighted material.