[pulseaudio-discuss] Stream volume API

[arun at accosted.net]

Hi folks,
Following from the discussion on flat volumes, here's a patch series to
enable a stream volume API. The API itself makes sense from a client
perspective independent of the flat volume discussion.

One thing worth noting is that I've got a single callback for
notifications of both volume and mute settings. My thinking was that
while this makes the API not quite as symmetric as it could be, from a
client perspective, this is likely more sensible. I'm open to being
persuaded otherwise, though. :)

I did try to implement a fallback mechanism to allow all of this to work
without protocol changes, using the subscribe API. This turned out to be
hairier than expected since we'd have to do a bunch of extra bookkeeping
to ensure callback order is kept the same as the newer API across
multiple concurrent async calls. The fallback mechanism can be revisited
if we want to, independently of this patch set (the tests make it easy
to verify basic functionality).

Cheers,
Arun