From VDR Wiki
The audiochannelselect patch lets the user switch between the different audio channels of a broadcast (both channels, only left, only right,...).
Applying the patch
If the patch is compressed you have to unpack it before
Now you can install it with
cd $SOURCEDIR/VDR patch -p 1 < /path/to/patch
Note, VDR has to be recompiled now, see VDR installation.