Re: [Jack-Devel] routing alsa through jack

On 12/17/2013 07:51 PM, Lucio Crusca wrote:
> Hello everybody,

Hi Lucio,

> I'm new here and I'm not a Jack developer, but I couldn't find any users 
> mailing lists and this page [1] says that «If you're doing anything with jack, 
> you need to be on this list», so I assumed users are welcome here...

yes, it's called jack-devel, but caters for users, too.

[..snip..]

> Now I'd like to make a conference call with Skype (Alsa only, I don't want to 
> add pulseaudio) and record it using my Jack toy. I need to record both mic and 
> output, obviously.

[..snip..]

> My solution involves snd_aloop.

Entirely appropriate. That approach works just fine here with older
versions of skype that support plain ALSA (I think newer versions of
skype are pulse only, but I don't know. I'm still using skype 2.2.0.25 I
just tested, still works). It gets me sound out of flash or any other
non-jack app.

Did you find
http://alsa.opensrc.org/Jack_and_Loopback_device_as_Alsa-to-Jack_bridge
? It's somewhat verbose, but a very nice article with complete
step-by-step instructions and background information.

> $ aplay -f FLOAT_LE -D hw:9 /usr/share/sounds/alsa/Front_Right.wav
> Warning: format is changed to S16_LE

Long story short: You cannot write directly to the loop-hardware once
alsa_in/out are connected. You'll have to use an 'aggregated' device or
alsa-plug configured in a $HOME/.asoundrc (or similar).

Here 'aplay -d aduplex /usr/share/sounds/alsa/Front_Right.wav'
works (but that's also the default) so just aplay .../file.wav

I use zita-ajbridge which is a drop-in replacement for alsa_in/out but
that's just a detail.

Here my ~/.asoundrc and a script to launch the bridge, which works here:

asoundrc: http://robin.linuxaudio.org/tmp/asoundrc-loopback

 zita-a2j -L -d hw:Loopback,1,0 -j cloop -n 2 -p 256
 zita-j2a -L -d hw:Loopback,1,1 -j ploop -n 2 -p 256
 sleep 1
 jack_connect cloop:capture_1 system:playback_1 &>/dev/null
 jack_connect cloop:capture_2 system:playback_2 &>/dev/null
 jack_connect system:capture_1 ploop:playback_1 &>/dev/null
 jack_connect system:capture_2 ploop:playback_2 &>/dev/null

A more complex example and the details are described in the alsa wiki
article linked above.

HTH,
robin

1387310016.3840_0.ltw:2, <52B0ABB6.8010109 at gareus dot org>