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[New: openFATE 318813] ALSA: Improved dmix defaults for multi-channel audio
Feature added by: Martin Herkt (lachs0r)

Feature #318813, revision 1
Title: ALSA: Improved dmix defaults for multi-channel audio

openSUSE Distribution: Unconfirmed
Priority
Requester: Desirable

Requested by: Martin Herkt (lachs0r)
Partner organization: openSUSE.org

Description:
For those who still reject PulseAudio in favor of ALSA’s dmix, there’s a
small but significant improvement to the default configuration with regard to
multi-channel audio sources. Currently, the default dmix device is limited to
stereo sources, which means that playing surround sound sources necessitates
exclusive access. Having to make sure nothing else is using the underlying
hardware when trying to watch a movie is not nice. There’s a relatively
trivial solution to this, using the upmix plugin, which is included with the
alsa-plugins package. In general, I see no reason not to install this package,
seeing as it also includes the Speex resampler (which is used automatically if
available, and without which audio quality will be severely degraded for
sources that need to be resampled by ALSA first).

The only known case where this does not “just work” is when audio hardware
exposes channels as multiple stereo pair subdevices instead of a true
multi-channel card (e.g. EMU10K1), but this hardware is a special case anyway
(and a somewhat rare one these days), and I’m sure workarounds are possible.

Test Case:
https://github.com/mpv-player/mpv/wiki/ALSA:-Surround-Sound-and-Upmixing

I wrote this article for users of mpv. It contains an example asoundrc. So to
test this, make equivalent changes to the default dmix configuration and try
playing a surround sound file with e.g. mpv (or use speaker-test) while
something else is playing e.g. a stereo stream via the default device. Playback
should not fail, and both sources should output sound to the appropriate
channels (i.e. the stereo source should be upmixed and mpv should detect the
correct channel map automatically, applying downmixing as necessary).

Use Case:
Playing audio from several applications with different channel configurations
(e.g. stereo system notifications and a media player playing a surround sound
file).

Business case (Partner benefit):
openSUSE.org: For some users, PulseAudio does not solve any problems (and in
fact still is the source of some), or they may prefer dmix for other reasons,
but with the current default configuration, just watching movies or playing
games can be inconvenient, as it would require exclusive access to the sound
hardware, and in some cases (e.g. openal-soft) editing configuration files just
to get the channel mapping right.


--
openSUSE Feature:
https://features.opensuse.org/318813

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