[pulseaudio-discuss] [RFC] Source Output Volumes

[Arun Raghavan]

On Fri, 2011-06-17 at 12:15 +0100, Colin Guthrie wrote:
> 'Twas brillig, and Colin Guthrie at 20/05/11 09:50 did gyre and gimble:
> > Hello,
> > 
> > As some of you know I've been working on restoring a little more
> > symmetry to our API to allow the adjustment of source output (capture
> > stream) volumes.
> > 
> > In the past, when stream volumes were added to sink inputs, it was
> > thought that this feature wouldn't be overly useful for capture streams
> > and while this argument still holds true, there is one feature that has
> > since been added to PA that would make it useful - flat volumes.
> > 
> > Flat volumes allow for multiple streams to be connected to the same
> > device and when they differ in stream volume, the maximum one is chosen
> > and the h/w is set to that, with the difference in volume between the
> > streams applied in software. This in theory allows for optimum power
> > efficiency where the software stays out of the loop whenever possible.
> > 
> > With flat volumes, adding per-stream volumes to capture streams makes sense.
> > 
> > It does also simplify client code when they want to adjust their own
> > volumes, they don't have to implement their own asymmetry to deal with ours.
> > 
> > 
> > So I am proud to announce my work to try and achieve this. There are no
> > doubt still bugs, so a thorough review is very much appreciated.
> > 
> > I will not post patches to the list (unless screamed for) as some of
> > them are necessarily rather large (+400 and +2k lines in the biggest
> > patches).
> > 
> > Most of the code is mirrored from the sink or sink input side. There is
> > a lot of scope to cut down on code duplication but for the purposes of
> > getting this out there I'll leave that for after the next release.
> > 
> > In some cases, applying the patch and comparing e.g. sink.c with
> > source.c is a better way of reviewing the changes (while there are still
> > several differences it isn't too hard to compare them).
> > 
> > I originally added support for synchronised streams for recording but
> > then realised that this makes little sense practically and removed it
> > again. I did the removal in a separate commit as it may be easier to
> > compare the sink vs. source files before this patch to cut down on
> > asymmetry)
> > 
> > Known niggles;
> > There are still some strange things with volumes. The flat volume stuff
> > doesn't seem to work perfectly as when adjusting a recording stream
> > volume down from NORM, the h/w volume does not drop... only when the
> > hardware volume has been moved down to 0 and back to NORM does flat
> > volume stuff work seem to work properly.
> > 
> > I think there are still a few niggles with volume setting generally (for
> > outputs too) as I still have a problem reported earlier that the initial
> > volume of things is disconnected to the h/w state and while PA thinks
> > it's got 100% it's actually not... I still need to look at that properly.
> > 
> > So without further ado, here is the branch for review:
> > http://colin.guthr.ie/git/pulseaudio/log/?h=master-source-volume
> > git://colin.guthr.ie/pulseaudio (master-source-volume branch)
> > 
> > For convenience of testing you can also use this patch to pavucontrol:
> > http://colin.guthr.ie/git/pavucontrol/log/?h=master-source-volumes
> 
> Any further comments on this or can I merge?

Sorry -- I actually did try the code again but missed you on IRC, then
went out of circulation for a few days. I'll add fixes for the
passthrough and echo-cancel bits after you merge, they should be pretty
small. I tested with multiple parec streams and it all looks good.

I did notice something weird though -- with gnome-sound-recorder (which
uses pulsesrc), adjusting the stream volume made the client whose volume
I adjusted get only noise. Not sure what's happening there, and haven't
had a chance to dig in yet. Other than this obviously being a problem
for pulsesrc, would be nice to figure this out so we know if other
clients also need fixing.

Cheers,
Arun