What's wrong with volume=0?

The reason that soundcards have a mute property is because there may be multiple
mixers, and you want them to remember the volume from before it was muted. For
applications such as Totem, it is application-specific and thus a knowledgeable
application could use volume=0 for mute.

This forces the application to cache the value of the volume, and restore it
when removing the mute, which makes the application more complicated, and
violates the encapsulation principles of object programming. 

Your slider is not the same widget as the mute button. It caches the value for
you already.

heh, sound-server doesn't have sliders...

then cache it in your sound-server, ok? :).

then what's the point of the volume plugin having a mute property ?

I don't know.

Look, my issue with this is that we're currently proxying all sort of properties
in playbin by adding it to playbin; that sucks. I'd rather use something like
gstpropertyproxy for that, or something else.

the better idea may be to have the "volume" property return a pointer to the
volume plugin itself, then the app does whatever it wants with the plugin...
if I understand correctly, the volume plugin never gets destroyed, so the app
could cache it

No, I'd rather use the property proxy interface Stefan did for this.

This is fixed for playbin with the current-audio property (set it to -1 to mute) and for playbin2 with a mute property.