[alsa-devel] Disable conversions

Lennart Poettering mznyfn at 0pointer.de
Sun Nov 25 21:41:32 CET 2007

On Wed, 21.11.07 12:40, Takashi Iwai (tiwai at suse.de) wrote:

> At Tue, 20 Nov 2007 01:51:51 +0100,
> Lennart Poettering wrote:
> > 
> > 4) If I open an audio device with "plughw:" i can disable the software
> >    resampling that takes place via
> >    "snd_pcm_hw_params_get_rate_resample()". However, there is no
> >    equivalent for disabling the channel number adjustment or the
> >    sample format conversion. This would be very useful in PA however,
> >    since this would allow me to use only the parts of plughw I am
> >    interested in (softvol), and disable all the rest (resampling,
> >    conversion, channel remixing).
> Hmm..  It's a bit difficult to implement in a clean way.
> For example, what would be the reason to disable softvol?  

Hmm, I think there's some kind of misunderstand here: softvol is the
only part I am interested in to use. It's the resampling, the sample
type conversion, and the channel map changing I want to disable. Right
now, I can only disable the resampling, but the type conversion and
channel conversion always stay enabled. Or did I miss something?

> It's basically irrelevant with the PCM parameters.  It's added just
> because of lack of hardware volume controls.
> One idea I have is to make an API like
> 	snd_pcm_alias_plugin(src, dst);
> For example,
> 	snd_pcm_alias_plugin("softvol", "passthru");
> would take passthru plugin instead of softvol plugin.
> (Suppose passthru plugin as a simply pass-through plugin to its
>  slave.pcm)

I am not sure if I understand what this would be useful for?


Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net         ICQ# 11060553
http://0pointer.net/lennart/           GnuPG 0x1A015CC4

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