Re: Required/preferred multichannel order for ALSA

[Liam Girdwood <lrg@ti.com>]

On Thu, 2012-04-26 at 16:33 -0500, Ricardo Neri wrote:
> Hi Takashi, list,
> 
> I am implementing multichannel support for HDMI on Texas Instruments' 
> OMAP4. I would like to know if ALSA mandates a specific channel order or 
> has a preferred one.
> 
> I tried to find some guidance in alsa-lib or in the alsa driver. All I 
> could find is the order described in speaker-test: 
> FL/FR/RL/RR/C/LFE/SL/SR. This order seems to be in use due to historical 
> reasons [1]. It was also mentioned that an API to set/get the channel 
> mapping was going to be implemented [2]; I tried to find it without 
> success. As [1] and [2] are very old posts, I was wondering if the 
> situation has changed.
> 
> My question arises from the fact that HDMI audio uses the channel 
> ordering defined in CEA-861 section 6.6.2, which is different from what 
> speaker-test expects. This also different from the order that SMPTE 320M 
> specifies. OMAP4 is able to alter the channel mapping, so I could match 
> what ALSA expects if such required/preferred order exists.
> 
> Thanks in advance for your comments.
> 
> Ricardo
> 
> 
> [1].http://www.spinics.net/lists/alsa-devel/msg24444.html
> [2].http://www.spinics.net/lists/alsa-devel/msg24495.html

A lot of hardware now can remap channels to suit the use case so it
would probably be good to have an ALSA API to get/set the mappings.

This seems like it would be a good subject for the BoF.

Liam