[pulseaudio-discuss] ask about passthrough support

[Arun Raghavan]

On Wed, 2011-09-07 at 14:20 +0800, Lu Guanqun wrote:
> Hi Arun,
> 
> I have several things unclear about passthrough support:

I'm talking about this work at Linux Plumbers' Conference on Friday. If
videos are available, I'll link to them -- hopefully that should make
the motivation clear.

> 1. Is it only useful when there's hardware decoding functionality
> available? Can I simply test out passthrough with the current ALSA sound
> card (some emulations possible)?

Pretty much. The whole idea is that you're pushing out compressed audio,
so something needs to decode it -- an a/v receiver that does AC3/DTS, or
a Bluetooth headset that supports MP3 decode.

> 2. As right now, ALSA only have PCM interface, how do we pass the
> encoded data down? Do we have to use some other driver specific
> interfaces? Vinod, recently posted some patches to add compression
> interface for ALSA. Is that needed?

No, that's not needed. We currently do IEC61937 payloading to make 

> 3. To be able to use passthrough, do we still need changes on Gstreamer?
> Therefore people can simply use something like 'gst-launch xxx'. And
> how's that status?

The base stuff is in git master, and some of it is en route
(https://bugzilla.gnome.org/show_bug.cgi?id=657179).

Regards,
Arun