[alsa-devel] Channel mapping

Clemens Ladisch cladisch at fastmail.net
Thu Nov 22 10:17:54 CET 2007

Jaroslav Kysela wrote:
> On Wed, 21 Nov 2007, Takashi Iwai wrote:
> > Indeed, the mixer <-> PCM mapping can be useful.  For such
> > information, the fixed size struct isn't suitable as multiple mixer
> > elements correspond to a single PCM channel.
> I think that we have already such interface, but maybe not well described 
> and used. I would propose to use SNDRV_CTL_ELEM_IFACE_PCM for PCM mixer 
> related controls and device & subdevice from control_id structure. In this 
> way, we can easy group and assign all control elements to PCM substream.

At the moment, this is only used for sound cards that have multiple

> We may have only one problem - to identify which elements are mixer 
> related and which are not. Maybe, we can use one bit from access flags to 
> determine, if it's a mixer control element if interface != MIXER.

I'm not sure if this information (mixer or not) is that useful - an
application is likely to access a mixer control with a 'known' meaning,
like volume or mute, and in this case it has to search the controls by
their name anyway.


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