[alsa-devel] Disable conversions

[Takashi Iwai]

At Wed, 21 Nov 2007 16:16:21 +0100 (CET),
Jaroslav Kysela wrote:
> 
> 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).

Or, we may provide a simpler way to change the local configurations
dynamically without changing the config file.  Change the default
configuration to be more selective, e.g. skip softvol if a certain
config vaiable is set, or so.


Takashi