[pulseaudio-discuss] digital devices (spdif)

[Jens Peters]

>On Mon, 05 Jan 2009 18:09:55 +0100, Lennart Poettering wrote:

Hallo and thanks a lot for your reply.

> The first part is to support SPDIF at all (i.e. for PCM), the next step
> is than to add pass-through CODEC support. It is rather unlikely that we
> will add compression/decompression support for codecs other than the
> free ones (vorbis) anytime soon. That means pass-through support for
> AC3/MP3 is all we can do, i.e. no volume control, no mixing, no nothing.

I think that is what everybody want with pass-through, just passing the 
bitstream from a movie without any modification to an external decoder :) 
I guess that most people don't want to hear eg. messenger sound events 
when watching a movie. The only thing that PA should ensure is, that the 
used sink is not used by other stuff when AC3/DTS starts/plays so that 
the external decoder can recognize the AC3 or DTS signal.
 
> As mentioned the problem is that we cannot really detect which setups of
> a device are incompatible with each other and which ones are not. My
> plans for the Fedora 11 release is to add easy support for changing
> these setups, and -- for the ALSA case -- detect them at initialization
> time by trying since that's the only option we have right now. I.e. we
> try to open the sound card for playback/capturing in different
> configurations (such as Stereo, 7.1, SPDIF, for playback and capturing)
> and see what works together. Then we compile a list for that and allow
> the user to quickly select one of the available configurations for each
> device during runtime and without interrupting playback. 

That sounds actually quite cool.

> I don't think PA is the right place to do matrix encoding/decoding. But
> if someone provides me with a good patch and the patent situation is
> somewaht clear I might be convinced otherwise...
> 
> Also note that ALSA has an ac3 plugin.

Yes, I know, but unfortunately it seems rather forgotten :( (I haven't 
test it though). About PA as the place for live encoding, for me its 
really just the same like post processing with the small difference that 
just the format changes and not what you hear (more or less ;)). 
Furthermore the configuration and usage of PA is so much more convenient 
than understanding and editing alsa configuration files. (And if dreaming 
keeps on, I would also prefer DTS live encoding above AC3)

Jens

(Btw: I hope that I don't mix up stuff :))