[pulseaudio-discuss] AMD chipset HDMI and SPDIF outputs lack surround sound modes

[Tanu Kaskinen]

On Sat, 2012-07-21 at 13:43 -0500, Yfrwlf wrote:
> Hello,
> 
>      I'm running Ubuntu 12.04 with two computers both with AMD video 
> chipsets.  Both of the sinks I need to output sound on have no mode 
> setting in Gnome sound config.  The analog outputs show surround options 
> available, but S/PDIF and HDMI options only offer stereo output.  Is 
> there some way in which I can contribute to enhance Pulseaudio so that 
> future versions will have this corrected?

S/PDIF is limited to two channels, unless you use some compressed format
(AC3 or DTS). You can use those compressed formats if you set up the
encoder plugins in the alsa configuration. PulseAudio uses the "a52" and
"dca" alsa devices if they exist.

It's not entirely clear to me what's missing from surround HDMI support.
IIRC, there are some problems to be solved (I think help here would be
much appreciated) before it can be supported, but on the other hand, the
extra-hdmi.conf profile set configuration file
(in /usr/share/pulseaudio/alsa-mixer/profile-sets) seems to already have
definitions for 5.1 surround. default.conf doesn't have those
definitions. extra-hdmi.conf is only used with NVidia and Intel
chipsets. I think the purpose of extra-hdmi.conf is to expose all the 4
hdmi devices that those chipsets have, but I don't know why there's a
difference in the surround handling. Maybe this is a bug, and
default.conf should have the surround definition too?

I hope someone more knowledgeable will clarify this.

>      On a separate topic, is there a way to force it to output with more 
> channels until a patch is applied?  I've tried messing around with pacmd 
> and can't figure out how to set the channels.  Does this need to be done 
> through editing one of the config files?

The channel configurations are determined by the profile set
configuration files, so familiarize yourself with the files
in /usr/share/pulseaudio/alsa-mixer/profile-sets (or
src/modules/alsa/mixer/profile-sets in the source tree). Some
documentation is in default.conf and this wiki page:
http://www.freedesktop.org/wiki/Software/PulseAudio/Backends/ALSA/Profiles

-- 
Tanu