Play a movie as screensaver in KDE

Did you ever want to play a video as screensaver? With KDE this is pretty easy.

1. you need a video player. I choosed mpv, but mplayer will also do.
2. you need a video. Store it in a public readable place, for example in /opt/cats.mp4. This is not exactly required in a single-user environment, but since your screensaver will be available to all users it is a nice idea. Of course you could also place it in another directory like /etc/screensaver and/or symlink to the real file. This will make it easier to replace the actual video file.
3. create a custom screensaver service file for KDE:

/usr/share/kde4/services/ScreenSavers/kcats.desktop:

[Desktop Entry]
Exec=mpv --loop=inf -ao=null /opt/cats.mp4
Icon=kscreensaver
Type=Service
X-KDE-ServiceTypes=ScreenSaver
Actions=Setup;InWindow;Root;
Name=Custom Video

[Desktop Action InWindow]
Exec=mpv --loop=inf -ao=null --no-keepaspect --wid=%w /opt/cats.mp4
Name=Display in Specified Window
NoDisplay=true

[Desktop Action Root]
Exec=mpv --loop=inf -ao=null --no-keepaspect --wid=0 /opt/cats.mp4
Name=Display in Root Window
NoDisplay=true

On an Intel NUC I had also to append '-vo=x11' to the option's list.

The exact location of the ScreenSavers directory may depend on your distribution. If unsure, try to locate it with:

$ find /usr -type d -name ScreenSavers

4. Finally, open the Lock Screen menu from KDE's settings and select your custom screensaver.