[API] add interface for volume level meters
Submitted by Lutz Mueller
Link to original bug (#510654)
Description
I propose merging the applications gst-mixer (GNOME's mixer application) and vu-meter (GNOME's volume level meter application) by integrating vu-meter into gst-mixer (i.e. volume level shown in the background of the scales using gst_range_set_fill_level).
The problem: gst-mixer uses GStreamer, but vu-meter uses esd. I need an GStreamer interface for getting the current volume level on a given track. In terms of ALSA, I need an interface that uses functions like snd_ctl_elem_read and snd_ctl_elem_value_get_integer to read the current level on a specific alsa device.