Post Syndicated from Lennart Poettering original https://0pointer.net/blog/projects/device-reservation.html

The JACK folks and I have agreed on a little specification for device
reservation that allows clean hand-over of audio device access from
PulseAudio to JACK and back. The specification is generic enough to allow
locking/hand-over of other device types as well, not just audio cards. So, in
case someone needs to implement a similar kind of locking/handover for any kind of resource here’s some
prior art you can base your work on. Given that HAL is supposed to go away
pretty soon this might be an option for a replacement for HAL’s current device
locking. The logic is as simple as it can get. Whoever owns a certain service name on
the D-Bus session bus owns the device access. For further details, read the spec.

There’s even a reference
implementation available, which both JACK2 and PulseAudio have now
integrated.

Also known as PAX SOUND SERVERIS.

Post Syndicated from Lennart Poettering original https://0pointer.net/blog/projects/bizarre-fun.html

#nocomments y

So I wanted to hack proper channel mapping query support into libsndfile, something I have had
on my TODO list for years. The first step was to find the source code
repository for it. That was easy. Alas the VCS used is bzr. There are some
very vocal folks on the Internet who claim that the bzr user interface is
stupendously easy to use in contrast to git which apparantly is the very
definition of complexity. And if it is stated on the Internet it must be true.
I think I mastered git quite well, so yeah, checking out the sources with bzr
can’t be that difficult for my limited brain capacity.

So let’s do what Erik suggests for checking out the sources:

$ bzr get http://www.mega-nerd.com/Bzr/libsndfile-pub/

Calling this I get a nice percentage counter that starts at 0% and ends at, … uh, 0%. That gives me a real feeling of progress. It takes a while, and then I get an error:

bzr: ERROR: Not a branch: "http://www.mega-nerd.com/Bzr/libsndfile-pub/".

Now that’s a useful error message. They even include an all-caps word! I guess that error message is right — it’s not a branch, it is a repository. Or is it not?

So what do we do about this? Maybe get is not actually the right verb. Let’s try to play around a bit. Let’s use the verb I use to get sources with in git:

$ bzr clone http://www.mega-nerd.com/Bzr/libsndfile-pub/

Hmm, this results in exactly same 0% to 0% progress counter, and the same useless error message.

Now I remember that bzr is actually more inspired by Subversion’s UI than by git’s, so let’s try it the SVN way.

$ bzr checkout http://www.mega-nerd.com/Bzr/libsndfile-pub/

Hmm, and of course, I get exactly the same results again. A counter that counts from 0% to 0% and the same useless error message.

Ok, maybe that error is bzr’s standard reply? Let’s check this out:

$ bzr waldo http://www.mega-nerd.com/Bzr/libsndfile-pub/
bzr: ERROR: unknown command "waldo"

Apparently not. bzr actually knows more than one error message.

Ok, I admit doing this by trial-and-error is a rather lame approach. RTFM! So let’s try this.

$ man bzr-get
No manual entry for bzr-get

Ouch. No man page? How awesome. Ah, wait, maybe they have only a single unreadable mega man page for everything. Let’s try this:

$ man bzr

Wow, this actually worked. Seems to list all commands. Now let’s look for the help on bzr get:

/bzr get
Pattern not found  (press RETURN)

Hmm, no documentation for their most important command? That’s weird! Ok, let’s try it again with our git vocabulary:

/bzr clone
Pattern not found  (press RETURN)

Ok, this not funny anymore. Apparently the verbs are listed in alphabetical order.
So let’s browse to the letter g as in get. However it doesn’t
exist. There’s bzr export, and then the next entry is bzr
help (Oh, irony!) — but no get in-between.

Ok, enough of this shit. Maybe the message wants to tell us that the repo
actually doesn’t exist (even though it confusingly calls it a “branch”). Let’s
go back to the original page at Erik’s site and read things again. Aha, the
“main archive archive can be found at (yes, the directory looks empty, but
it isn’t): http://www.mega-nerd.com/Bzr/libsndfile-pub/“.
Hmm, indeed — that URL looks very empty when it is accessed. How weird though
that in bzr a repo is an empty directory!

And at this point I gave up and downloaded the tarball to make my patches
against. I have still not managed to check out the sources from the repo.
Somehow I get the feeling the actual repo really isn’t available anymore under that address.

So why am I blogging about this? Not so much to start another flamefest, to
nourish the fanboys, nor because it is so much fun to bash other people’s work or
simply to piss people off. It’s more for two reasons:

Firstly, simply to make
the point that folks can claim a thousand times that git’s UI sucks and bzr’s
UI is awesome. It’s simply not true. From what I experienced it is not the
tiniest bit better. The error messages useless, the documentation incomplete,
the interfaces surprising and exactly as redundant as git’s. The only
effective difference I noticed is that it takes a bit longer to show those
error messages with bzr — the Python tax. To summarize this more positively: git excels as much as bzr does. Both’ documentation, their error messages and their user interface are the best in their class. And they have all the best chances for future improvement.

And the second reason of course is that I’d still like to know what the correct way to get the sources is. But for that I should probably ask Erik himself.

Post Syndicated from Lennart Poettering original https://0pointer.net/blog/projects/copyright.html

Here’s a little a little tool I
wrote that automatically generates copyright headers for source files in a
git repository based on the git history.

Run it like this:

~/projects/pulseaudio$ copyright.py src/pulsecore/sink.c src/pulsecore/core-util.c

And it will give you this:

File: src/pulsecore/sink.c
	Copyright 2004, 2006-2009 Lennart Poettering
	Copyright 2006-2007 Pierre Ossman
	Copyright 2008-2009 Marc-Andre Lureau
File: src/pulsecore/core-util.c
	Copyright 2004, 2006-2009 Lennart Poettering
	Copyright 2006-2007 Pierre Ossman
	Copyright 2008 Stelian Ionescu
	Copyright 2009 Jared D. McNeill
	Copyright 2009 Marc-Andre Lureau

This little script could use love from a friendly soul to make it crawl entire source trees and patch in appropriate copyright headers. Anyone up for it?

Post Syndicated from Lennart Poettering original https://0pointer.net/blog/projects/tagging-audio.html

So you are hacking an audio application and the audio data you are
generating might eventually end up in PulseAudio before it is played. If that’s the case then please make sure
to read this!

Here’s the quick summary for Gtk+ developers:

PulseAudio can enforce all kinds of policy on sounds. For example, starting
in 0.9.15, we will automatically pause your media player while a phone call is
going on. To implement this we however need to know what the stream you
are sending to PulseAudio should be categorized as: is it music? Is it a
movie? Is it game sounds? Is it a phone call stream?

Also, PulseAudio would like to show a nice icon and an application name next
to each stream in the volume control. That requires it to be able to deduce
this data from the stream.

And here’s where you come into the game: please add three lines like the
following next to the beginning of your main() function to your Gtk+
application:

...
g_set_application_name(_("Totem Movie Player"));
gtk_window_set_default_icon_name("totem");
g_setenv("PULSE_PROP_media.role", "video", TRUE);
...

If you do this then the PulseAudio client libraries will be able to figure out the rest for you.

There is more meta information (aka “properties”) you can set for your application or for your streams that is useful to PulseAudio. In case you want to know more about them or you are looking for equivalent code to the above example for non-Gtk+ applications, make sure to read the mentioned page.

Thank you!

Oh, and even if your app doesn’t do audio, calling g_set_application_name() and gtk_window_set_default_icon_name() is always a good idea!

Post Syndicated from Lennart Poettering original https://0pointer.net/blog/projects/versioning-dbus.html

So you are designing a D-Bus interface and want to make it future-proof. Of
course, you thought about versioning your stuff. But you wonder how to do that
best. Here are a few things I learned about versioning D-Bus APIs which might
be of general interest:

Version your interfaces! This one is pretty obvious. No explanation
needed. Simply include the interface version in the interface name as suffix.
i.e. the initial release should use org.foobar.AwesomeStuff1, and if
you do changes you should introduce org.foobar.AwesomeStuff2, and so
on, possibly dropping the old interface.

When should you bump the interface version? Generally, I’d recommend only
bumping when doing incompatible changes, such as function call signature
changes. This of course requires clients to handle the
org.freedesktop.DBus.Error.UnknownMethod error properly for each function
you add to an existing interface. That said, in a few cases it might make sense
to bump the interface version even without breaking compatibility of the calls.
(e.g. in case you add something to an interface that is not directly visible in
the introspection data)

Version your services! This one is almost as obvious. When you
completely rework your D-Bus API introducing a new service name might be a
good idea. Best way to do this is by simply bumping the service name. Hence,
call your service org.foobar.AwesomeService1 right from the beginning
and then bump the version if you reinvent the wheel. And don’t forget that you
can acquire more than one well-known service name on the bus, so even if you
rework everything you can keep compatibilty. (Example: BlueZ 3 to BlueZ 4 switch)

Version your ‘entry point’ object paths! This one is far from
obvious. The reasons why object paths should be versioned are purely technical,
not philosophical: for signals sent from a service D-Bus overwrites the
originating service name by the unique name (e.g. :1.42) even if you
fill in a well-known name (e.g. org.foobar.AwesomeService1). Now,
let’s say your application registers two well-known service names, let’s say
two versions of the same service, versioned like mentioned above. And you have
two objects — one on each of the two service names — that implement a generic
interface and share the same object path: for the client there will be no way
to figure out to which service name the signals sent from this object path
belong. And that’s why you should make sure to use versioned and hence
different paths for both objects. i.e. start with
/org/foobar/AwesomeStuff1 and then bump to
/org/foobar/AwesomeStuff2 and so on. (Also see David’s comments about this.)

When should you bump the object path version? Probably only when you
bump the service name it belongs to. Important is to version the ‘entry point’
object path. Objects below that don’t need explicit versioning.

In summary: For good D-Bus API design you should version all three: D-Bus interfaces, service names and ‘entry point’ object paths.

And don’t forget: nobody gets API design right the first time. So even if
you think your D-Bus API is perfect: version things right from the beginning
because later on it might turn out you were not quite as bright as you thought
you were.

A corollary from the reasoning behind versioning object paths as described
above is that using / as entry point object path for your service is a
bad idea. It makes it very hard to implement more than one service or service
version on a single D-Bus connection. Again: Don’t use / as entry
point object path. Use something like /org/foobar/AwesomeStuff!

Post Syndicated from Lennart Poettering original https://0pointer.net/blog/projects/writing-volume-control-uis.html

Writing modern volume control UIs (i.e. ‘mixer tools’) is much harder to get
right than it might appear at first. Because that is the way it is I’ve put
together a rough
guide what to keep in mind when writing them for PulseAudio. Originally
just intended to be a bit of help for the gnome-volume-control guys I believe
this could be an interesting read for other people as well.

It touches a lot of topics: volumes in general, how to present them,
what to present, base volumes, flat volumes, what to do about multichannel
volumes, controlling clients, controlling cards, handling default devices,
saving/restoring volumes/devices, sound event sliders, how to monitor PCM and
more.

So make sure to give it at least a quick peek! If you plan to write a volume
control for ncurses or KDE (hint, hint!) even more so, it’s a must read.

Maybe this might also help illustrating why I think that abstracting volume
control interfaces inside of abstraction layers such as Phonon or GStreamer is
doomed to fail, and just not even worth the try.

And now, without further ado I give you ‘Writing Volume Control UIs’.