[alsa-devel] [RFC] Channel mapping API

Mark Brown broonie at opensource.wolfsonmicro.com
Tue Aug 21 18:27:06 CEST 2012

On Tue, Aug 21, 2012 at 05:38:34PM +0200, Clemens Ladisch wrote:
> Takashi Iwai wrote:

> > It's an interesting idea.  But, in the case of HDMI, there are no
> > multiple jacks, so this won't fit.  [...]
> > The primary goal of this API is to provide a way for apps to decide
> > the channel map for multi-channel streams.

> Indeed; including the jack location/type would go beyond what the
> channel map is useful for.  Playback applications know what kind of
> multichannel stream they're playing, but they definitely do _not_ want
> to decice if the output should go to the front or back panel.

> The channel mapping is a _stream_ configuration, the other routing
> choices are device setup.

Perhaps I'm missing something but why would the availability of
additional information be a problem for applications here?  The idea was
purely to punt the description of the outputs attached to the stream to
somewhere we already need to use to describe the outputs rather than
having to map the two formats together.

> At the moment, we lack an API to provide topology information.  But
> whatever form it takes, it should probably be independent of the channel
> mapping.  (I'll see if I can find time to do something about my media
> framework patches until next week.)

For media controller?  Everyone who's looked at in detail has expressed
concern about it being too heavyweight...
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