[mythtv-users] SPDIF and analog audio simultaneously

[Kevin Kuphal]

J. Scott wrote:

> Thanks to a lot of information from this archive, I was able to get my 
> SPDIF output working properly using my nForce onboard audio.
>
>  
>
> I'm still working on the issue of being able to output analog audio 
> simultaneously with SPDIF. I distribute the audio and video throughout 
> my house via a rf modulator that requires an analog audio signal. For 
> this purpose, I have to always have analog audio enabled.
>
>  
>
> I recently got a 6.1 home theater set up, so I'd like to be able to 
> send a digital audio signal directly to the receiver. I really only 
> need this feature for MythVideo and maybe MythMusic.
>
>  
>
> So I'm looking for ideas on how to either:
>
>  
>
> 1. Have the audio output delivered in both analog and digital format 
> simultaneously. Everything I've seen so far indicates that you have to 
> specify a single device (analog or digital) for the audio output. I 
> wonder if a solution might include using a separate soundcard, or 
> using some of the other 5.1 channels built into the onboard soundcard???
>
>  
>
> OR
>
>  
>
> 2. Devise a simple way to switch between digital output and analog 
> output, preferrably using the remote control. This is reasonably easy 
> with MythTV and MythMusic, but I can't see any way to do it in 
> MythVideo without altering the mplayer command line- a little tricky 
> from the remote!
>
>  
>
> Worst case I guess I could get a cheap front-end (xBox?) to put in the 
> cabinet with the home theater receiver. I believe the xBox supports 
> SPDIF output.
>
>  
>
> Thanks for the ideas!
>
I think what you're looking for is the ALSA PCM plug-in "dshare"

Something like this in your .asoundrc:

pcm.dualchannel {
    type share
    slave spdif
    bindings.0 0
    bindings.0 1
    }
}

Now, I might have the bindings mixed up as I've never done this, but you 
can see the reference material from ALSA here:

http://www.alsa-project.org/alsa-doc/alsa-lib/pcm_plugins.html#pcm_plugins_dshare

I think what it means is you define pcm.dualchannel as your default ALSA 
device like:

pcm.!default {
 type plug
 slave.pcm "dualchannel"
 }

And the dual channel definition takes the spdif output and maps channel 
0 to channel 0 and channel 0 to channel 1.  I think that means that your 
digital would be hw:0,0 and your analog hw:0,1 (thus channel 0 and 1 on 
card 0)

Hope this helps,
Kevin