+ use a more correct naming scheme to match the one from Spa
+ remove the default video source, since we now use a different
 session for video

This is mostly useful when using the adapter with audiotestsrc,
which supports an infinite number of channels. By specifying
a preference, we can limit it to the number of channels that we want.

* there is just one link, no need for a list
* warn if something goes wrong and don't assert