Re: PCM API questions

[Takashi Iwai <tiwai@suse.de>]

At Mon, 24 Jun 2002 08:49:25 -0400,
Paul Davis wrote:
> 
> >> 2.  How is device selection designed to work with ALSA?  My experience
> >> with ALSA has been very confusing in this regard.  I recall reading at
> >> least once that ALSA is not designed to have applications enumerate all
> >> the devices; that the correct way is to use ~/.asoundrc to define a
> >> hardware device and then supply that name to applications.  But is there
> >> anything more sophisticated an application can do than to just present
> >> the user with a text box?
> >
> >the pcm name really depends on the driver implementation.
> >usually, device #0 is provided for general use.  but, for example, the
> >implementation of 4-channel sound is driver speicific.
> >some driver implements using a control switch and other combines
> >multiple pcm streams, etc.
> >
> >however, there are standard names, too:
> >default, front, rear, center_lfe, surround40, surround51, spdif and
> >iec958 (identical with spdif).
> >it would be nice if users can choose one of them from a list, and
> >additionally have an input text field (well, not sophisticated,
> >though).
> 
> but there's no straightforward method of determining which names
> actually exist. the code in aplay that handles the -L request, for
> example, is baroque to the point of extremity. an application could
> not just use those standard names, because the audio interface they
> have may not support them.
 
yep.  that's actually a problem, too.
the names above are not defined on all cards (except for default).
i think we need a kind of config database for each card.
this is useful not only for pcm but also for parsing the mixer
structure.


> in addition this also doesn't deal with the issue of users with more
> than one soundcard installed.

this is not difficult, since the card number can be passed via
CARD argument.


Takashi


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