[LAU] Jack fallback to alsa when firefire device off?

[Robin Gareus]

On 02/17/2011 07:16 AM, Mike Cookson wrote:
> 
> 
> 
> Wed, 16 Feb 2011 11:27:42 -1000 письмо от Joel Roth
> <joelz at pobox.com>:
> 
>> On Wed, Feb 16, 2011 at 11:14:21PM +0300, Mike Cookson wrote:
>>> Is there such thing? It is not my question, it saw it on irc. And
>>> really
>> could not find nothing.
>> 
>> Not sure I understand the question fully.
>> 
>> If you are using JACK-based apps, you will always want JACK
>> running, whichever audio device is available. If your apps don't
>> require JACK, then why bother to use it?
>> 
>> It sounds like you want some facility to run JACK under certain
>> conditions. I believe there are some hooks in udev that will let
>> you run a script, for example when a firewire device is plugged in.
>> That script could start jackd.
>> 
>> You don't mention the type of app; if it's a recorder/player/mixer
>> thing, Nama (based on Ecasound) automatically *detects* JACK,
>> falling back to ALSA if necessary.
>> 
>> cheers,
>> 
>> 
>> -- Joel Roth


> I mean feature, that if firewire device is off, jack should switch to
> alsa - like it switches to dummy on suspend.

The problem is that JACK will shut-down or crash when you disconnect the
device, before any HAL (udev) can react and tell JACK to switch back-ends.

Possible options and solutions to this have been discussed on the
JACK-devel list end of 2010 but nothing has been implemented, yet.

The largest concern is that there is no way of knowing how to retain and
map port connections. e.g. the 1394 devices may have 8 in/out while the
build-in ALSA only has two; there are other details too (e.g.
sample-rate, device config, etc)

It may be an option to run JACK on top of pulseaudio, and have
pulseaudio switch the devices, but this is just a kludge and not
recommended in any way.

ciao,
robin

-- 
Robin Gareus
web: http://gareus.org/                mail: robin at gareus.org
lab: http://citu.fr/                   chat: xmpp:rgareus at ik.nu

Public Key at http://pgp.mit.edu/  http://gareus.org/public.asc
Fingerprint : 7107 840B 4DC9 C948 076D 6359 7955 24F1 4F95 2B42