multiple audio applications (JACK)

guldo · 01-02-2007, 06:00 PM

Hello
I'm trying to run several audio applications at once.
I mean, if I run mplayer and mpg321 at the same time, I can listen to both; there are some applications that cannot work like this though.
Some do not start until the audio device is available, and get hold of the device when they start, so that the device become unavailable.

How can I run those applications at once?
I thought I could use JACK, but I can't understand how am I supposed to use it...

Code:

# jackd -R -d alsa
jackd 0.101.1
Copyright 2001-2005 Paul Davis and others.
jackd comes with ABSOLUTELY NO WARRANTY
This is free software, and you are welcome to redistribute it
under certain conditions; see the file COPYING for details

JACK compiled with System V SHM support.
loading driver ..
creating alsa driver ... hw:0|hw:0|1024|2|48000|0|0|nomon|swmeter|-|32bit
control device hw:0
configuring for 48000Hz, period = 1024 frames, buffer = 2 periods
nperiods = 2 for capture
nperiods = 2 for playback

Code:

# alsaplayer -o jack audio_04.wav
Failed to load output plugin "jack". Trying defaults.
ALSA lib pcm_dmix.c:864:(snd_pcm_dmix_open) unable to open slave
snd_pcm_open: Dispositivo o risorsa occupata (default)
Failed to initialize plugin!
/usr/lib/alsaplayer/output/libalsa_out.so failed to load
NOTE: THIS IS THE NULL PLUGIN.      YOU WILL NOT HEAR SOUND!!

Any help?

Linux: 2.6.18
alsa is compiled from source (1.0.13)
Jack is installed from the debian package:
# jackd --version
jackd version 0.101.1 tmpdir /dev/shm protocol 15

ronkymac · 01-03-2007, 09:04 AM

jack is an audio server: think of it as a patchbay for audio.

the command #jackd ... started up the audio server. Now, all the programs connect through that server. The next step is to route the audio through each application so as to get an output, so the best way to do this is use a frontend. There's a few available, but by far the most popular is QJackCTL - http://qjackctl.sourceforge.net/

install that, and get it running - it's pretty intuitive, but if you need any help then get back to linuxquestions.org.

Regards,
Ronald.

guldo · 01-03-2007, 11:05 AM

Thanks for the reply.
So I start jack using that gui; then I run, for example:
# mplayer -ao jack whatever.wav
It works.
But I have two problems:
1) mplayer has a jack option; what can I do with applications that do not have it?
2) sound comes with an annoying noise; don't know why... I tried some values for rate/frames/realtime...

Emerson · 01-03-2007, 01:10 PM

There is dmix for ALSA, does the same job. I think it's included with latest ALSA.

guldo · 01-03-2007, 01:21 PM

Thanks, that's interesting, too!

Anyway, I still cannot understand how can I use it with any application...
I set up a .asoundrc to use the dmix plug, and tried soon after with aplay; it works fine.
But how can I make any application use it? This I can't understand...
:help:

Emerson · 01-03-2007, 02:15 PM

http://www.linuxquestions.org/questi...d.php?t=446651

guldo · 01-03-2007, 06:19 PM

Great!
I just had to load the oss modules, start the application via aoss and select the oss device for its output

No need for jack.

Thank you!