Re: Channel modes feature request.

[Takashi Iwai <tiwai@suse.de>]

At Tue, 12 Aug 2003 10:25:50 +0100,
James Courtier-Dutton wrote:
> 
> Takashi Iwai wrote:
> > At Tue, 12 Aug 2003 00:19:34 +0100,
> > James Courtier-Dutton wrote:
> > 
> >>I have a SB live audio card.
> >>I can open it with device names like: -
> >>surround40 (Front Left, Front Right, Rear Left, Rear Right)
> >>surround51 (Front Left, Front Right, Rear Left, Rear Right, Center, LFE)
> >>
> >>There is a requirement for: -
> >>surround41 (Front Left, Front Right, Rear Left, Rear Right, LFE)
> >>surround50 (Front Left, Front Right, Rear Left, Rear Right, Center)
> >>
> >>How can I get alsa to support these ?
> > 
> > 
> > i still don't understand your question quite correctly.
> > 
> > do you mean open a multi-channel (5ch) pcm stream wihh the
> > configuration above?
> > if so, it's not too difficult for sb live (but not always easy for
> > other cards).  it would look like:
> 
> Can you expand on why. Because it seems sensible to me that all cards 
> that do surround51, can also do surround50 and surround41.

ok, so you mean a generic support for these formats.

> If by what you say, it is not possible (when I say not possible, I mean 
> not possible with adding extra memcpy's to move the channels around in 
> alsa-lib) , then I will adjust my application to use the surround51 pcm, 
> and just mute the un-needed channel.

well, after thinking a bit more, it turned out that it's easy to do
this in generic way (but with an overhead, of course).

e.g. surround41 can be derived from surround51 such as

pcm.surround41 {
	type route
	slave.pcm surround51
	ttable.0.0 1
	ttable.1.1 1
	ttable.2.2 1
	ttable.3.3 1
	ttable.4.5 1
}

we can define this as a default while the optimized version can be
defined in each card definition (as written in my previous post).


Takashi


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