Re: [Jack-Devel] ALSA PCM substreams

Gabriel M. Beddingfield wrote:
> When opening a PCM, would it make sense for JACK to open all the
> substreams on that PCM?

No.  PCM devices with multiple substreams typically use them for
hardware mixing.  (When opening a device without an explicitly
specified substream number, ALSA chooses the first free substream.)

> I was helping a user on IRC with the Audio 4 DJ, a 4-in/4-out USB
> sound card.  The card uses the `caiaq' driver in ALSA.  It didn't
> "just work" because the 4 channels are split up into stereo
> substreams.  So, when jack opens "hw:1,0", it opens "hw:1,0,0"
> (2 channels) and ignores "hw:1,0,1" (2 more channels).[1]

The driver should have used two devices instead of two substreams.
(But automatically opening multiple devices would not necessarily be
a good idea either.)

> I spoke with the developers of the `caiaq' driver, and they said it
> would make sense for JACK to go ahead and open all the substreams.

Only for this particular device.


A useful feature would be the ability to specify multiple device names,
and Jack automatically constructing a "multi" device for them.


Regards,
Clemens

1386085031.11834_0.ltw:2, <529DFA9E.9060509 at ladisch dot de>