[alsa-devel] [RFC] Channel mapping API (take 2)

Tanu Kaskinen tanuk at iki.fi
Wed Sep 5 08:00:12 CEST 2012

On Tue, 2012-09-04 at 17:47 +0200, Takashi Iwai wrote:
> The rest aren't so much changed.  Only slight bug fixes.

I have a couple of comments about "the rest". I haven't been following
the development of the channel map API very closely, so I'm relying on
the pcm.h file only.

/** channel map list type */
enum snd_pcm_chmap_type {
	SND_CHMAP_NONE = 0,	/** unspecified channel position */
	SND_CHMAP_FIXED,	/** fixed channel position */
	SND_CHMAP_VAR,		/** freely swappable channel position */
	SND_CHMAP_PAIRED,	/** pair-wise swappable channel position */

It's not clear to me what the VAR and PAIRED types actually mean. It
would be nice to explain in more detail the concepts in the header.

The snd_pcm_chmap_position enum doesn't contain an entry for mono. I
think it would be a useful channel to have. Up/downmixing decisions may
be different with mono than, for example, a single channel declared as
front left.


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