[alsa-devel] Use of default device with snd_pcm_link()

[Jaroslav Kysela]

O Sun, 27 Dec 2009, Devin Heitmueller wrote:

> I am working on some code which captures from one PCM device and plays
> to another, based off of the latency.c found in alsa-lib.  I noticed
> something strange:
>
> The code works if I set the capture device to hw:1,0 and playback
> device to hw:0,0.  However, if I change the playback device to
> "default:0", the snd_pcm_link() call fails with -ENOSYS (error 38).
>
> If I dump out the properties, I can see that the the default device
> *is* mapped to device 0,0, so it's not clear why the behaviour would
> differ.
>
> My goal was just to playback to whatever the default device is, and I
> was under the impression that default:0 should be equivalent to
> "hw:0,0".  Can anyone offer any brief explanation as to why the
> snd_pcm_link() call would fail?

Some alsa-lib plugins do not have the link feature implemented. If you use 
snd_pcm_dump(), you may list all plugins in chain. I think that dmix is in 
path. And no, "default:0" is NOT equivalent to "hw:0,0".

 						Jaroslav

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Jaroslav Kysela <perex at perex.cz>
Linux Kernel Sound Maintainer
ALSA Project, Red Hat, Inc.