(experimental) automatic sound mixing

[Colin Walters]

Hi,

I spent a bit of time today on an ALSA-level sound mixing solution, i.e.
this bug:

https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=130593

Basically my solution was to allocate the IPC keys at the start of the X
session, and generate an ALSA config file on login which uses those
keys.  This avoids issues with possible IPC key collisions and is more
secure.  There's a little program alsa-launch which does this.  It
monitors your X connection and destroys the IPC keys and such when you
log out.

I had to patch alsa-lib to let it read a config from a file specified an
environment variable.  alsa-launch is part of alsa-utils now.  I'm sure
some people will complain this makes alsa-utils dependent on X; I guess
we'll need an alsa-utils-x11 package.

Also, I needed to add alsa-launch to the X startup; however there was no
programmatic way to do this in the current xinitrc setup.  So I
refactored the X init scripts so that packages can drop a file
in /etc/X11/xinit/xinitrc.d/ which adds to the DESKTOP_SERVICES
environment variable.  I then modified the dbus package to use this new
variable.

All the new packages are here:
http://people.redhat.com/walters/alsa/

These are based off the new ALSA 1.0.7 packages I uploaded to rawhide
today.

I'd like to get feedback on this and see how well it works for people;
I've just done some light tests with ogg123, rhythmbox, and xmms.
Particularly interesting is recording and complex ALSA applications.
Oh, and multiple sound cards.

If there are no objections I'd like to feed this all into rawhide in a
few days after it's gotten a bit of testing here and see how things go.
Hopefully for FC4 the idea of configuring applications for different
sound output backends will totally disappear.

Longer term of course I'd like to not have to generate an ALSA config
file in /tmp; this kind of thing just makes sense inside the alsa-lib
code itself.  But this was just a quick one-day hack to see how well
asym could work as the default.

Comments appreciated.

[Bill Nottingham]

Colin Walters ([e-mail]) said:
> Longer term of course I'd like to not have to generate an ALSA config
> file in /tmp; this kind of thing just makes sense inside the alsa-lib
> code itself.

Why /tmp instead of $HOME? (In fact, why doesn't alsa-lib by default
read configs out of $HOME to override /etc anyway?)

Bill

[Colin Walters]

On Thu, 2005-01-06 at 23:22 -0500, Bill Nottingham wrote:
> Colin Walters ([e-mail]) said:
> > Longer term of course I'd like to not have to generate an ALSA config
> > file in /tmp; this kind of thing just makes sense inside the alsa-lib
> > code itself.
>
> Why /tmp instead of $HOME? (In fact, why doesn't alsa-lib by default
> read configs out of $HOME to override /etc anyway?)

NFS home dirs.

[Mike Hearn]

On Thu, 06 Jan 2005 22:55:59 -0500, Colin Walters wrote:
> I had to patch alsa-lib to let it read a config from a file specified an
> environment variable.

Maybe we could set the environment variable to the IPC key itself
then use something like:

pcm.dmix {
        @args [ SLAVE FORMAT RATE ]
        @args.SLAVE {
                type string
                default "hw:0,0"
        }
        @args.FORMAT {
                type string
                default S16_LE
        }
        @args.RATE {
                type integer
                default 48000
        }
        type dmix
        ipc_key {
    	@func getenv
    	vars [ ALSA_DMIX_IPC_KEY ]
    	default { 12345678 }
        }
        ipc_key_add_uid no
        slave {
                pcm $SLAVE
                format $FORMAT
                rate $RATE
        }
}

pcm.!default {
      type plug
      slave "pcm.dmix"
}

which is a slightly modified version of the default ALSA config file. Then
there'd be no need to generate config files or patch alsalib.

And yes, I know, possibly ALSA should not provide a mini API in its config
file but well that's an argument for upstream :) We have it, might as well
use it ...

thanks -mike

[Colin Walters]

On Fri, 2005-01-07 at 13:26 +0000, Mike Hearn wrote:
> On Thu, 06 Jan 2005 22:55:59 -0500, Colin Walters wrote:
> > I had to patch alsa-lib to let it read a config from a file specified an
> > environment variable.
>
> Maybe we could set the environment variable to the IPC key itself
> then use something like:

Good idea.  I hacked this up a bit to fix some bugs and add a few more
default buffer size bits, and uploaded it and alsa-launch to rawhide.

Once this patch goes in:
https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=144554
alsa-launch will run and asym should be transparently enabled.

[Mike Hearn]

On Sat, 08 Jan 2005 01:30:57 -0500, Colin Walters wrote:
> Good idea.  I hacked this up a bit to fix some bugs and add a few more
> default buffer size bits, and uploaded it and alsa-launch to rawhide.

Cool. If this works out it'd be nice to get alsa-launch upstream and have
some document on the ALSA wiki explaining how other distribution vendors
can set this up.

thanks -mike