[mythtv-users] SPDIF output works for MythMusic, but not MythTV

[Brad Benson]

On Fri, 18 Mar 2005 14:48:15 -0600, Andrew Close <aclose at gmail.com> wrote:

> you can buy a male to male stereo patch cable and plug one end into
> the output of your pvr-350 and the other into the input of your sound
> card.  when you listen to music it will be the same as usual.  when
> you watch tv you should now get sound out of the SPDIF port.
> not pretty, but it should work.

I've got a related problem and it's been driving me nuts for quite a
while now.  I have a pvr350 and a zoltrix nightingale soundcard
(c-media CM8738 using cmpci kernel module).  I have the 350 audio
outputs linked into the line in of the soundcard and both spdif
optical and stereo rca connections from the soundcard outputs to my
receiver's inputs.  I've tried the instructions in the
DigitalSoundHowTo on mythtv.info that say to set "Analog to IEC958
Output" to on in alsamxer.  The problem is that alsamixer has a
setting labeled just IEC958 Output which seems to have no effect
whether it is on or off.  There is another setting labeled IEC958
Loop.  My understanding of this setting is that it pipes the analog
input back out through the spdif output.  However, when I enable this
setting I am very clearly getting analog audio coming into the
receiver, but sound works for all parts of myth.  (I know this because
I can disconnect the spdif cable and still get sound, but when I
disconnect the analog cables sound goes away.)  When I disable this
setting I get audio over the spdif connector for MythMusic, MythVideo,
MythDVD, etc.  Everything EXCEPT tv.  The only way I've found so far
to get sound from tv over the spdif connector is to use the
instructions from the DigitalSoundHowTo for Via sound chips.  The
problem there is that the only way to get that to work is to issue
this command from the command line:

arecord -D hw:0,0 -fdat | aplay -D mixed-digital

This works perfectly for outputting tv audio over the spdif connector,
but there is no way to automatically execute that command every time
myth plays a recording and if I leave that command running all the
time I get double audio from all other parts of myth (music, video,
etc).

Has anyone else had a similar problem?  Is anyone else using a cmpci
sound device succesfully using spdif output for all parts of myth? 
The sound quality I get over spdif is obviously much better than the
analog connections, but right now I'm stuck using analog for
everything in order to avoid having to switch audio inputs when using
different parts of myth (because that's too much for the GF to handle
;).

Thanks,
Brad