[mythtv-users] RE: Configuring SPDIF digital out.

Nick knowledgejunkie at gmail.com
Sat Dec 17 20:07:59 EST 2005

On 17/12/05, Marius Schrecker <marius at schrecker.org> wrote:
> > I might suggest that all alsa utilities, alsactl, and everything else is
> > NOT required
> > to use digital out with MythTV.  I'm using MythTV 0.18.1 on Gentoo and I
> > only
> > have the necessary alsa drivers compiled in the kernel. I've never used
> > alsamixer
> > or alsactl, or installed/emerged alsa-utils, alsamixer, aplay, or anything
> > else
> > alsa related. I'm not starting any alsa services during startup. The only
> > thing I did is:
> >
> > Enable alsa support and driver in the kernel.
> > Put .asoundrc in my home directory.
> > Set MythTV as follows:
> >   -Enable AC3
> >   -Device = "ALSA:digital"
> >   -Mixer = "digital"
> >
> > and that's it.  I also have all the other mythplugins working by setting
> > their device
> > to ALSA:digital. Is my setup unique, or are people doing more than need to
> > to get digital audio working?
> >
> The simpler the better. I don't care how little is installed as long as I
> can get digital output, so far no go, everything looks as if it should be
> working, just no sound :(
> I'd love to know how to test spdiff out as simply as possible, if I can
> bypass aplay then so much the better!
> Can I stream a 48KHz file straight to spdiff out?

You can use aplay -D <pcmdevice> and then send it out of your spdif
whilst testing. You can get a list of all PCM devices by running aplay
-L - choose one that your SPDIF is aliased to (commonly spdif) and see
if you get any sound.

The digital sound HOWTO really does explain everything you should need
to do to get SPDIF output - the one hurdle is commonly determining
which controls in the mixer need to be set to allow this. In my most
basic asoundrc file (which sounds everything by default to my SPDIF) I
have used:

pcm.!default {
type hw
card 0
device 1

The card/device to specify can be determined using `aplay -l` - for my
system my SPDIF was given as device 1 - yours may be different. Note
that this device expects 48kHz audio - if it's not the same format it
may play back too slow/fast or not at all. The excellent asoundrc in
the HOWTO uses the plug and dmix plugins to allow on-the-fly rate


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