Hi Fons,
On 08/02/2023 12:09, Fons Adriaensen wrote:
Hello all,
I've been contemplating trying out Pipewire as a replacement
for Jack. What is holding me back is a what seems to be a
serious lack of information. I'm not prepared to spend a lot
of time and risk breaking a perfectly working system just to
find out that it was a bad idea from the start. So I have a
lot of questions which maybe some of you reading this can
answer. Thanks in advance for all useful information.
I'm really glad you raise the questions...
I feel in the same situation (more as a user) and still find Pipewire
quite confusing.
I recently reinstalled my uses Manjaro (Arch-based) and I see I _do_
have a 'pipewire' package installed, but it looks like I'm actually
running pulseaudio (?) and am able to run jack and use my
jack-pulseaudio sink _if_ needed - as I have usually done since years.
That's confusing enough, my intuition is that pipewire (at least on Arch
and Arch-based distros) is some sort of 'metapackage' (the upstream
points to pipewire.org) and then the actual functionality is in the
myriad of pipewire-* packages such as pipewire-audio, pipewire-alsa,
pipewire-jack.
Then I see that pipewire-jack conflicts with both jack and jack2 which
makes me very very reluctant to install them as a replacement (I use
jack2): on my older machine I gave it a go and Ardour wouldn't even start.
I don't want to sound over-critical, just as you (and maybe other users)
I'm simply pretty confused. The documentation, at least for me, also
seems a bit confusing when it comes to JACK [1].
It might just be a matter of time, meaning Pipewire is still a
relatively new project and quite ambitious I'd say. I'd also imagine
that (understandable) it's mostly focusing on desktop audio (/video) and
not on pro audio.
A first thing to consider is that I actually *like* the
separation of the 'desktop' and 'pro audio' worlds that
using Jack provides. I don't want the former to interfere
(or just be able to do so) with the latter. Even so, it may
be useful in some cases to route e.g. browser audio or a
video conference to the Jack world.
I agree. For me pulseaudio is 'everyday' non-pro-audio, jack for
pro-audio and then if needed use a sink. Quick and easy and good to have
two distinct approaches. If I'm recording or making audio I'm
(typically) not watching youtube videos et. al.
So, I'm also really interested in the questions you pose (and possible
answers).
So the ideal solution
for me would be the have Pipewire as a Jack client.
So first question:
Q1. Is that still possible ? If not, why not ?
I think the final aim of Pipewire is to _replace_ JACK. It's not clear
for me if the option to run JACK 'natively on demand' is considered a
kind of transitionary phase or will remain. If the latter maybe one
could consider (and use) Pipewiere eventually as Pulseaudio is used today?
If the answer is no, then all of the following become
relevant.
Q2. Does Pipewire as a Jack replacement work, in a reliable
way [1], in real-life conditions, with tens of clients,
each maybe having up to a hundred ports ?
Q3. What overhead (memory, CPU) is incurred for such large
systems, compared to plain old Jack ?
A key feature of Jack is that all clients share a common idea
of what a 'period' is, including its timing. In particular
the information provided by jack_get_cycle_times(), which is
basically the state of the DLL and identical for all clients
in any particular period. Now if Pipewire allows (non-Jack)
clients with arbitrary periods (and even sample rates)
Q4. Where is the DLL and what does it lock to when Pipewire
is emulating Jack ?
Q5. Do all Jack clients see the same (and correct) info
regarding the state of the DLL in all cases ?
The only way I can see this being OK would be that the Jack
emulation is not just a collection of Pipewire clients which
happen to have compatible parameters, but actually a dedicated
subsystem that operates almost independently of what the rest
of Pipewire is up to. Which in turn means that having Pipewire
as a Jack client would be the simpler (and hence preferred)
solution.
As said, this (at least logically), sounds really similar to the
pulsaudio-jack sink concept... For instance what I now have in a script
is something along the lines of:
pactl load-module module-jack-sink
pactl load-module module-jack-source
and get pulseaudio as an in/out jack client.
[1] which means I won't fall flat on my face in front of
a customer or a concert audience because of some software
hickup.
Ciao,
Lorenzo
[1] https://gitlab.freedesktop.org/pipewire/pipewire/-/wikis/JACK
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