[pulseaudio-discuss] {PATCH][RFC] AC3 passthrough support

Michael Rans mcarans at yahoo.co.uk
Sun Jul 11 01:43:44 PDT 2010

At the moment I can switch between A52 and stereo SPDIF but it requires file 
editing and restarting Pulseaudio. 

1. I haven't tried the new profiles yet - does this mean with the profiles in a 
GUI, I would be able to switch from A52 to stereo SPDIF output without editing 
any files or restarting Pulseaudio? 

2. Would I be able to switch while music is playing between stereo and A52 and 
back (as is currently possible between my SPDIF and HDMI on different 


From: Tanu Kaskinen <tanuk at iki.fi>
To: pulseaudio-discuss at mail.0pointer.de
Sent: Sun, 11 July, 2010 6:47:14
Subject: Re: [pulseaudio-discuss] {PATCH][RFC] AC3 passthrough support

On Sat, 2010-07-10 at 15:40 +0000, Michael Rans wrote:
> Regarding AC3 encoding in Pulseaudio - it would be better because at
> the moment switching between stereo and A52 is not possible (ie. I
> cannot have both these lines in default.pa:
> load-module module-alsa-sink device=Filter_RateConvert rate=48000
> sink_properties=device.description=AC3 sink_name=AC3
> load-module module-alsa-sink device=ALC889A_Digital
> sink_properties=device.description=SPDIF sink_name=SPDIF
> Presumably the SPDIF out is locked by one of them, then the other
> fails. With ac3 encoding in Pulseaudio, this would be switchable
> without editing any files.

Switching between stereo and a52 does not require doing the encoding in
pulseaudio. Pulseaudio already provides both stereo and a52 spdif
profiles for alsa cards with spdif output. The a52 profile uses the alsa
plugin to do the encoding. The only problem is, as you know, that the
a52 alsa plugin doesn't seem to work with pulseaudio (at least without
the rate converter workaround). Fixing the plugin (or pulseaudio, if the
cause actually is in pulseaudio) instead of implementing ac3 encoding in
pulseaudio would be a perfectly fine solution.

Tanu Kaskinen

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