[pulseaudio-discuss] PulseAudio doesn't seem to find my HDMI audio card

[Colin Guthrie]

'Twas brillig, and Marie-Noëlle Augendre at 09/06/11 18:44 did gyre and
gimble:
> 2011/6/9 Colin Guthrie <gmane at colin.guthr.ie <mailto:gmane at colin.guthr.ie>>
>     OK, so now you have set your "normal" sound card to Off. Is this
>     intended?
> 
> 
> I thought it was one, or the other. Can I have both àt the same time?
> What for?

So that you can swap your sounds from different applications between
them as you wish. e.g. you may want to have a monitor connected to your
regular DSUB 15 or DVI but have a nice HD TV hooked up to your HDMI. You
could play videos+sound on your HD TV but have your regular desktop and
regular sounds on your "normal" monitor. Lots of use cases for this.

>     Normally I'd expect you to want to keep both cards available but only
>     use the one you want at any given time.
> 
> 
> I didn't even know there were 2 cards in that laptop when I bought it. I
> only want the HDMI to work properly so I can listen to some music in
> good conditions. Why would I want to use the "bad" audio card?

Explained above. It all depends on your scenario. But if you don't want
the built in card, then yes, keep it turned Off.

>     Anyway, Firefox is able to output sound, but is that sound going to your
>     normal sound card or to your HDMI?
> 
> 
> My guess is it goes to the "normal" one, as I barely hear anything with
> the volume at 100%. Any other way to know for sure?

Erm, by listening which sound card from which the sound comes out.... It
should be very obvious which sound card a given app is using.

But, if you cannot tell then run:

sudo fuser -v /dev/snd/pcm*

This should tell you which cards which applications are using. TYpically
only pulseaudio should have your cards open. If any other app has a card
open, your system or the app is misconfigured. All alsa sound should be
routed to the "default" sound device which in turn shoud be configured
to go to PulseAudio via the alsa-pulse plugin. Your distribution should
ensure this is all configured for you, so assuming they have done that
and assuming you've not messed with that config it *should* work, but
it's worth double checking and asking your distro support channel how
they expect it to work in their deployment of PA.


>     If your normal sound card then firefox is bypassing PA and accessing the
>     h/w directly. THis can cause other apps to not be able to ouput.
> 
>     In your listing, I do not see any "Sink Input" (i.e. playback streams),
>     so that suggests no app is actually playing audio via PA at the time you
>     grabbed it. I would suggest that something is not configured correctly
>     at that level (e.g. are you apps using alsa output and is alsa not
>     configured correctly to use the PA plugin? If possible configure the
>     apps to use PA directly rather than going via the alsa plugin)
> 
> I don't know what alsa is (and I don't know much more about pulseaudio ...)

Alsa is the low level layer that actually communicates with the sound
h/w. Pulseaudio uses alsa to talk to the sound h/w. Applications can
either talk direct to alsa to talk to the hardware or talk to PA (which
in turn will talk to alsa to talk to the hardware) or the app can talk
to alsa, but have it intercepted and passed to pulseaudio before
ultimately going back to alsa to talk to the h/w. This last example may
sound bizarre (and to a degree it's a compatibility thing) but PA will
"talk to alsa" in a much more advanced way than any other alsa client
out there does, so it's well worth using it.

Anyway enough of the background. There are plenty other sources of
information out there on the web if you want to know more.


> Why are there 2 different programs?

Because you run more than one program at a time on a multi-tasking
operating system....

> And how are the other applications supposed to know which one to use?

What do you mean by "which one"? Do you mean which sound card if you
have two or which system (alsa vs. PA)?

If the former, initially they will use the "default" sound card in PA.
You can then move the application's sound streams to the device of your
preference via pavucontrol or similar mixer apps. PA will remember this
choice and restore it the next time you run the app.

If you mean alsa vs. PA, then the answer is simple. All applications
should use what they are capable of. It is the distro's responsibility
to ensure that if the app only supports alsa, that alsa is configured in
such a way that it will redirect sound to PulseAudio. As a user you
*shouldn't* have to worry about it, except when things are mis-behaving
or are misconfigured. I suspect that as a novice user you should
probably be going via your distributions support channels who can then
communicate with upstream projects after having gotten to the bottom of
your specific problems in the context of that distributions PulseAudio
deployment.


> I have looked at the settings in
> GMusicBrowser, RythmBox and VLC and didn't find anything that seems
> related to alsa or pulseaudio; so I don't know how to configure these
> applications.

Ryhtmbox use GStreamer so this should "just work" with PA. VLC has
multiple audio backends, you can choose which one you want. It's
typically set to Auto which will use PA if support is compiled and
installed. YOu may need to add an additional package from your distro's
software repository.


I'm not sure I can help you more unless you can get the basic
configuration correct such that applications are talking to PA in some
capacity (either directly or via ALSA). Your distribution support
channels should be able to help you in get this bit right as it does
vary from distro to distro as to how to check and configure this correctly.

Col


-- 

Colin Guthrie
gmane(at)colin.guthr.ie
http://colin.guthr.ie/

Day Job:
  Tribalogic Limited [http://www.tribalogic.net/]
Open Source:
  Mageia Contributor [http://www.mageia.org/]
  PulseAudio Hacker [http://www.pulseaudio.org/]
  Trac Hacker [http://trac.edgewall.org/]