FROM: http://xubuntu.org/news/screen-locking-in-xubuntu-14-04/
What happened to my music playback?
As your seat becomes inactive, your audio stream is stopped/paused until you log into your session again. This is one of the known issues of light-locker or locking with LightDM in general.
Currently, when locking, it is assumed you are either:
- in a public space of sorts (the desktop at home hardly needs
locking) and have walked away from the machine
- using a system with more than one user
Stopping/pausing playback in both of these scenarios make sense.
However, this might be an annoying change for users used to having their music playback continue even when their session locks. If you don’t like this behavior, there are basically two solutions:
- Set light-locker to lock the session “When the screensaver is
deactivated”
- Switch back to using xscreensaver
- Add your user to the “audio” group on your computer and music
playback will continue also with light-locker
The first option is a good workaround, because it means that your audio-playback will continue when the screen has been blanked. However, when you wake up your computer, e.g. by touching the mouse, it will pause the music until you log into your session again.
The third solution is mentioned last, because it isn’t advised to add your user to the “audio” group (read The Audio Group wiki page for a comprehensive explanation). However, as long as you’re on a single-user system, this might still be an option for you.