[gstreamer-bugs] [Bug 567660] [API] need a stream volume interface for sinks that do volume control

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=567660
  GStreamer | gst-plugins-base | git

--- Comment #16 from Sebastian Dröge <slomo at circular-chaos.org> 2009-09-11 14:13:20 UTC ---
(In reply to comment #12)
> One thing to keep in mind: if you define the interface like this it is only
> implementable by sinks that output to some software sound service, or to very
> few hardware devices. The reason for that is that not for all hardware we
> actually know the volume factor each possible volume step refers to. For
> example Bluetooth audio devices generally don't communicate which volume step
> means which amplification. They just offer an opaque integer in a range 0..15
> where 0 is somehow less loud than 15, but that's all we know. Something similar
> is true for many USB devices and so on.
> 
> Of course, this interface is about stream, not device volumes, so this probably
> isn't a real problem. And if some day we want to support 'opaque' stream
> volumes then we could still add another interface for that. But all I wanted to
> make sure is that this is kept in mind.

Sure, for that stuff we already have the GstMixer interface. This is only for
stream volumes.

> Two comments though: it might be worth adding comments that the dB scale you
> chose is for amplitude, not power. (i.e. 20*log10, not 10*log10).

Good idea, actually I wasn't sure if I should take amplitude or power. What
would you suggest to use?

> Also, you
> might want to add a comment making clear that the cubic scale should be used
> for presentation in the UI. And referring to
> http://www.robotplanet.dk/audio/audio_gui_design/ or
> http://lists.linuxaudio.org/pipermail/linux-audio-dev/2009-May/thread.html#23151
> might be a good idea, too.

That's already mentioned in the docs :)

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