Buy a license from Raspberry Pi site at http://www.raspberrypi.com/mpeg-2-license-key/
Before doing so you’ll need to get the serial number from the Raspberry Pi. This is NOT printed physically on the board.
Power up RaspBMC and go to Settings > Settings Information to get the IP address.
SSH into Pi on the default port using the following credentials:
Once paid, an email should be sent with
Edit the config.txt in /boot directory and add decode_MPG2 and decode_WVC1 as stated in the email.
Run the following commands to check if it’s enabled:
vcgencmd codec_enabled MPG2
vcgencmd codec_enabled WVC1