[pulseaudio-discuss] jack soundcard reservation behavior

[Lennart Poettering]

On Fri, 31.07.09 13:46, Fernando Lopez-Lezcano (nando at ccrma.Stanford.EDU) wrote:

> One question though, shouldn't pulseaudio have printed something when
> jack quits? (with -vvv) It does print when jack asks for the card. 

0.9.16 does, 0.9.15 doesn't take notice of that.

> > So with F12 you start jack, and rb stops and then you quit jack and rb
> > continues automatically.
> 
> Great. But do the streams stop playing or do they continue playing
> "muted" while the card is "borrowed" by jackd? If I use the pacmd
> suspend 1 trick they continue playing (muted, or sent to the equivalent
> of /dev/null, I don't know). 

The effect of pasuspend and this reservation lgoci stuff should be
mostly identical: the device is forcibly suspended playback
freezes. The client apps are notified about that and could show this
in the UI but almost no app doesd that and for them time just appears
frozen.

or with other words: not a single sample is dropped when PA's device
access is suspended.

> > > [*] for example it would allow for currently playing streams to be moved
> > > to a dynamically loaded jack plugin without missing a beat (or rather,
> > > with a very short interruption). Part of this is also implemented in my
> > > current script. 
> > 
> > I'd love to make PA automatically load a jack connectivity module when
> > JACK is started up. A simple way to implement that would be by
> > watching for JACK's service name to appear on the bus. But
> > unfortunately jack doesn't work that way and the running daemon does
> > not take name on the bus.
> 
> Couldn't jack notify when it is ready? (and furthermore when it is about
> to quit). It is already talking on dbus with pulseaudio... I'm pretty
> sure things are not so easy :-) It would also have to be something you
> could turn on/off when jack is started, maybe that would be the deal
> killer. 

Taking a name on the bus would be the perfect solution, since it makes
sure PA knows exactly when jack becomes available and when jack goes
away again. Also if jack dies abnormally D-Bus would clean up the name
automatically so this would even be very robust.

Lennart

-- 
Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net
http://0pointer.net/lennart/           GnuPG 0x1A015CC4