[vdr] How do I listen to a channel's soundtrack and it's audio description at the same time?

[John Robinson]

Hi everyone.  I've recently joined this list and am totally blind.  I've 
installed VDR and am using the vdr-softdevice plugin with SHM output 
under the Gnome desktop.  I would very much like to be able to hear a tv 
programme's soundtrack, together with the programme's audio description, 
when supported of course.  One member of this list very helpfully 
suggested that, to switch between the programme's main sound track and 
the audio description track, I can hit the 'Audio' key, then the right 
cursor key and then the 'Audio' key again.  This does, indeed switch 
from the main programme sound track to the audio description track, but 
it only lets me hear one or the other, not both.  I would very much like 
to hear the main programme's soundtrack and the audio description track 
at the same time, but at the moment, I can only hear one or the other - 
not both.  If anyone on this list could explain how to hear both the 
programme's soundtrack and the audio description track at the same time, 
I'd really appreciate it.

Many thanks for any help.

John