[pulseaudio-discuss] digital devices (spdif)

Colin Guthrie gmane at colin.guthr.ie
Sat Jan 3 04:10:13 PST 2009

'Twas brillig, and Jens Peters at 03/01/09 10:45 did gyre and gimble:
> Hello there,
> Before I begin I want to say that pulseaudio is really one of the coolest 
> peaces of software on Linux I have seen in the last years. It took me 
> some time to get the whole picture and where to place pulse exactly, but 
> once I got it the setup was quite easy (using Ubuntu  8.10 with Gnome and 
> a Vanilla KDE4 and of course pavucontrol).


> For the record, I'm using an 
> Intel HDA (Realtek ACL889A) card onboard and I use the digital output, 
> connected to and external AC3/DTS decoder (Teufel decoderstation3) and 
> headphones/microphone in the front.

> I wonder actually if there are any decisions made regarding AC3/DTS pass-
> through and may be life encoding. The only outsider regarding sound 
> output is AC3/DTS where I talk directly to alsa (mplayer -ao alsa -ac 
> hwac3,hwdts,). It would be very cool if I could do something like mplayer 
> -ao pulse -ac hwac3,hwdts,. The stream would show up in pulse control and 
> I can imagine that even moving the stream to another (digital) output 
> could realized. Obviously any other normal output on a digital output 
> would have been muted/discarded when pass-through output is started (At 
> the moment I have to make sure that there is no active output before 
> starting pass-through output). A second pass-through stream should also 
> be muted/discarded until the output is free again. (Actually I guess this 
> is the same work-flow as on Windows). I read somewhere that a big 
> showstopper for this is the detection of digital devices. Why not just 
> adding a module parameter for that, because I guess that most users, 
> including me, already have to add the digital output by hand, so e.g.: 
> load-module module-alsa-sink device=iec958:0 capabilities=spdif,..
> until hal/alsa gives some more information.

Well you clearly know the score and what needs doing to make it kinda 
work! I think you make good points about being able to dynamically 
reconfigure sinks etc with different options.

Lennart, do you have any plans in this area? I know that loading all the 
sub-cards on a device can lock off the previous ones, but perhaps the 
detection code can be tweaked to open+suspend, open+suspend each of them 
so that they are nto all enabled at the same time. And perhaps some 
auto-probing could then be done once all the devices are loaded to 
detect whether the devices are mutually exclusive etc. Don't know if 
this would be possible? If it is perhaps these mutually exclusive sinks 
can be presented to the user as a single sink but with "sink options" of 
some kind (e.g. 5.1 support, digial vs. analog vs. both, etc. etc.).

Is this totally unreasonable?

> Additionally having a post-processing module like ladspa for live 
> encoding like the windows counterparts Dolby Digital Live of even better 
> DTS Connect would made pulse the _real_ audio control software imho. But 
> I already read about license issues, I don't know what possibilities are 
> there :(  

Pulse can load ladspa processing :)

> Just to be sure: these are actually my ideas and nothing more :) (and not 
> at all meant as criticism or offensive). And if everything has been said 
> earlier then there is no need to respond either..

It's all good. There are lots of ideas and plans to make pulse better 
but they are not always written down clearly (I've got several proposals 
in my head myself that I've not written yet!)



Colin Guthrie

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   PulseAudio Hacker [http://www.pulseaudio.org/]
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