[alsa-devel] Disable conversions

[Jaroslav Kysela]

On Wed, 21 Nov 2007, Takashi Iwai wrote:

> At Wed, 21 Nov 2007 12:40:54 +0100,
> I 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?  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");

I don't like this idea nor implementation much. It will be much better to 
design a run-time communication with plugins to change configuration 
parameters / behaviour (something like ioctl on opened pcm handle).

					Jaroslav

-----
Jaroslav Kysela <perex at perex.cz>
Linux Kernel Sound Maintainer
ALSA Project