From VDR Wiki
All TV application here, besides Kaffeine, are using /dev/video, so a FF DVB card  is needed. They are useful to watch TV with VDR on your computer monitor, a TV is not necessary.
Kaffeine on the other hand is a self-contained application. It has the ability to watch digital TV independent from VDR.
- As these applications are permanently accessing the video device /dev/video it is locked for other application. Other programs like the screenshot-plugin or VDRAdmin are not (fully) working then.
- One should pay attention that the right video device is used for access (e.g. /dev/video0, /dev/video1, ...), as often webcams and analog TV card are initialised before the DVB card.