[pulseaudio-discuss] Expected level of ALSA/OSS compatibility

[CJ van den Berg]

On Tue, Apr 17, 2007 at 11:17:53AM +0000, Neilen Marais wrote:
> So, I'd like to know what is the ultimate level of ALSA/OSS compatibility
> that can be expected? Are there certain things that just can't be emulated
> by a non-kernel deamon?

For ALSA it should be possible to achieve close to perfect compatibility
because all ALSA client applications are supposed to use libasound, which
provides hooks for things like PulseAudio. Unfortunately though, there are a
couple issues though with the ALSA plugin at the moment, on both the ALSA
and PulseAudio sides of things, but it should hopefully get better soon.

With OSS it's a little different. It's almost impossible to achieve full
compatibility with the padsp approach (and it's been tried by ALSA and ESD
before with limited success). There is another approach though that actually
uses a kernel daemon and therefore promises perfect compatibility, but AFAIK
it's still in its early stages.  For more info checkout
https://www.redhat.com/archives/fedora-desktop-list/2007-January/msg00080.html

> I've googled a bit, but can't seem to find any definite answers. And if I
> find apps that don't want to work with the ALSA/OSS emulation, should I
> report them all as bugs?

If you can trace it to PulseAudio, sure. Although if the application already
has a native PulseAudio plugin that your distro isn't shipping, I suggest
you also report it with them. After all, native PulseAudio output is the
better way to go in most situations.

> FWIW, my experiences so far have been:
> 
> libao apps: Ubuntu ships the PA plugin, works like a charm.
> 
> XMMS: Ubuntu doesn't ship the pulseaudio plugin, so out of lazyness I
> tried talking to PA through both ALSA and ESD output plugins, neither of
> which worked. A connection seems to get created with pulseaudio (I can see
> "ALSA plug-in [xmms]" in paman), but xmms claims there is a problem with
> the audio device.  I compiled and installed the PulseAdio xmms plugin
> myself, which works, so I'm happy with XMMS support now.
> 
> Audacity: Can't get it to work; it simply doesn't list the PA ALSA
> devices, and gives me an error if I try to use padsp (see
> https://bugs.launchpad.net/ubuntu/+source/pulseaudio/+bug/107207 )
> 
> mplayer: Don't have the PA patch applied yet. PA ALSA emulation doesn't
> work, padsp strangely does work quite well.
> 
> totem-xine: Again the ubuntu version doesn't seem to include a PA plugin,
> but the PA ALSA emulation seems to work a treat.

The xmms, mplayer, xine and gstreamer plugins are all in Debian already, so
with a little luck they will probably make it into the next release of
Ubuntu too.

-- 
CJ van den Berg

mailto:cj at vdbonline.com
  xmpp:cj at vdbonline.com
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