On Sun, 16 Dec 2001, Paul Davis wrote:
> >What is a difference between an ASCII identifier "plughw:0,0"
> >and "hw:0,0"? And what the output of 'aplay -L' means?
>
> a "hw" device is totally constrained by the hardware characteristics
> of the underlying audio interface. if the device has 26 channels, then
> it must be used with 26 channels; if it only supports interleaved
> access, it must be used with interleaved access; if it doesn't support
> 16 bit output, you can't use it with 16 bit output.
>
> a "plug" device is unconstrained by all this. you can ask for any
> configuration you want, and ALSA will provide it for you.
>
> a "plughw" device is a slightly specialized version of a "plug"
> device, differing only in that the underlying PCM device being
> accessed is of type "hw". it has the same freedom as a "plug" device
> in all other ways.
>
> as a programmer, you do not need to worry about any of this. honest.
>
> >I just want to know a number of installed sound cards
> >and number of subdevices for every card and I'd like
> >to have a possibility to open the right card and a subdevice
> >according user's choice. I think that ALSA-0.5 interface was
> >much better in these things...
>
> well, most of us disagree with you, and some of us, rather vigorously.
>
> in ALSA 0.9, you do not attempt to "scan all cards and pick
> one". this is something that cannot be done reliably or usefully in
> many situations.
>
> you allow the user to specify the *name* of a PCM device they wish to
> use. these names correspond to entries in their ~/.asoundrc file, and
> may contain configurations that your program can't even imagine.
>
> case in point: my machine has (sometimes): 2 Hammerfall cards, 1
> Trident 4D-NX card, 1 Tropez+. The tropez audio playback is currently
> broken, so i never use it for that (but it has a decent wavetable
> synth and 2 MIDI ports); the hammerfall outputs are semi-permanently
> wired to my mixer and the the inputs of everything are up on a patch
> bay. occasionally, i run both hammerfalls as a single PCM device at
> 96kHz, more often as two separate devices.
>
> you will not be able to write a user friendly configuration program
> for my system. you can't do it in general, because the ALSA "plug"
> layer offers a totally flexible layer that allows an audio interface
> to appear to have any characteristics that you want.
>
> instead, just let your program take it from a user that when they tell
> it to use the ALSA PCM device "foo" that they know what they're
> doing. if the user does not specify a name, use "default" and it will
> work 99.8% of the time. the current setup of the "default" device is a
> "plughw" device using the first audio interface. it will work with any
> sample rate, any sample format, any type of access (interleaved,
> noninterleaved, read/write or mmap).
Interesting - and explains why I am having a hard time learning to use the
alsa library.
Could you explain to me how to do the following: the user has a TV capture
card with audio-out that is plugged in into one of the sound cards
installed in the system. I need to ask user which card and which input
s/he plugged the TV audio into. How do I do that ? (Preferably without the
user messing around with configuration files or entering names from
keyboard).
thanks !
Vladimir Dergachev
>
> --p
>
>
>
>
>
>
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