[Pkg-mpd-maintainers] Bug#568588: mpd: MPD default config doesn't allow multiple programs to share audio output via ALSA

[Max Kellermann]

On 2012/12/17 11:42, Yury Bulka <yurkobb at gmail.com> wrote:
> I completely agree with Konstantin Khomoutov. All the apps like web
> browsers and vlc are able to use dmix without any noticeable loss of
> sound quality.

That depends on your quality requirements.  dmix defaults to 48 kHz
and 16 bit.  Most music (all music ripped from CDs) is 44.1 kHz.  You
could argue that you don't hear a quality loss from resampling, but
quality is definitely lost, and more CPU is consumed for the
resampler.

Now if you're listening to high-quality 24 bit FLAC files, you're in
trouble: dmix will force you to throw away the additional 8 bits.
Maybe you can't hear that either, well ok, then that's your personal
requirement for audio quality.

> Also, vlc with dmix for some reason still uses less CPU
> than mpd without dmix.

If (the latest) MPD uses more CPU than *any* other software music
player, then this is either a configuration error, a different (more
expensive) resampler that MPD defaults to (can be configured), or a
bug.

If you think it's the latter, I'm very interested in fixing this
problem and optimizing MPD to make it faster again than the other
software.  Post your repeatable benchmark numbers comparing vlc/MPD
and a "perf report" of MPD to bugs.musicpd.org and I'll take care of
it.

However, this bug report is about MPD 0.15.8.  Much has changed, much
has been optimized since 0.15.  I will not opimize MPD 0.15, because I
have done that already, and it's called MPD 0.17.2.  Let's not beat a
dead horse.

> I believe that only realtime production-critical programs like jackd
> should use hw:0 by default. MPD is just another media player like vlc or
> mplayer. Alsa developers decided to enable dmix by default, and why we
> are reverting their decision on a per-program basis? Why ALSA has a
> "default" device at all then? Isn't it actually designed to be used by
> default?

dmix is per-user, but MPD usually runs as a different user (repeating
myself).  Given the severe disadvantages of dmix and its uselessness
when used by MPD, disabling it is a reasonable choice for me.  That's
just my opinion, and everybody can put his opinion in his mpd.conf.

Max