[alsa-devel] PCM parameters in file plugin

Jaroslav Kysela perex at perex.cz
Tue Jan 6 11:31:02 CET 2009

On Tue, 6 Jan 2009, Pavel Hofman wrote:

> Pavel Hofman napsal(a):
> > Hello,
> > 
> > I am working on a file plugin patch to allow adding PCM parameters 
> > (rate, format) to  the name of the file created (plus the ability to run 
> > an external command via popen, such as upsampling with sox). I got stuck 
> > in trying to obtain these parameters in pcm_file.c:_snd_pcm_file_open(). 
> > Is it actually possible or the information is not available at the time 
> > of opening the file (and the whole patch is thus nonsense)?
> > 
> > Thanks a lot for help.
> > 
> I am now opening the output file in pcm_file.c:snd_pcm_file_write_bytes.
> Surprisingly it seems to work fine. Could such hack be accepted as a
> patch to the plugin (if coded properly)? Is there a better place to open 
> the file?

The file should be opened in the hw_params callback (all PCM parameters 
are known in this time). Also, extending filename with PCM parameters 
should be optional (configurable). But the idea looks nice.


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

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