Removed autoaudiosink's device selection.

The way this code was testing devices locked the element to using the wrong
device. The incorrect device had a max volume of 39 on the Master track, really
making accurate volume changes impossible.

Instead of trying to make any guesses about this I'm leaving it to the element
to have sensible defaults.

Code will also ensure that it returns a newly created copy of the mixer, not
one we have already used.

mopidy/gstreamer.py

@@ -49,42 +49,34 @@ class AutoAudioMixer(gst.Element, gst.ImplementsInterface, gst.interfaces.Mixer)
             elif not factory.has_interface('GstMixer'):
                 continue
 
-            element = factory.create()
-            if not element:
-                continue
+            if self._test_mixer(factory):
+                return factory.create()
 
-            # Element has devices, try each one.
-            if hasattr(element, 'probe_get_values_name'):
-                devices = element.probe_get_values_name('device')
+        return None
 
-                for device in devices:
-                    element.set_property('device', device)
-                    if self._check_mixer(element):
-                        return element
+    def _test_mixer(self, factory):
+        element = factory.create()
+        if not element:
+            return False
 
-            # Otherwise just test it as is.
-            elif self._check_mixer(element):
-                return element
-
-    def _check_mixer(self, element):
         try:
-            # Only allow elements that succesfully become ready.
             result = element.set_state(gst.STATE_READY)
             if result != gst.STATE_CHANGE_SUCCESS:
                 return False
 
-            # Only allow elements that have a least one output track.
-            output_flag = gst.interfaces.MIXER_TRACK_OUTPUT
-            return bool(self._find_track(element, output_flag))
+            # Trust that the default device is sane and just check tracks.
+            return self._test_tracks(element)
         finally:
             element.set_state(gst.STATE_NULL)
 
-    def _find_track(self, element, flags):
-        # Return first track that matches flags. 
+    def _test_tracks(self, element):
+        # Only allow elements that have a least one output track.
+        flags = gst.interfaces.MIXER_TRACK_OUTPUT
+
         for track in element.list_tracks():
             if track.flags & flags:
-                return track
-        return None
+                return True
+        return False
 
     def list_tracks(self):
         return self._mixer.list_tracks()
@@ -452,7 +444,7 @@ class GStreamer(ThreadingActor):
          100 == max volume for given system.
         None == no mixer present, i.e. volume unknown.
 
-        :rtype: int in range [0..100]
+        :rtype: int in range [0..100] or :class:`None`
         """
         if self._mixer is None:
             return None