[mythtv-users] Outputting AC3/DTS in analog too?

Alen Edwards allen.edwards at oldpaloalto.com
Tue Jun 24 06:26:23 UTC 2008

Marc MERLIN wrote:
> My mythtv is connected into a denon AVR3808 receiver with a coax digital
> connection.
> This plays analog and digital audio just fine.
> Problem is that I would like to send my sound to my second TV so that I can
> display the same video/audio output to two TVs. I already have an HDMI
> splitter and my picture goes to both TVs.
> If my sound is analog, the denon receiver will also send it to its audio
> output, to my second TV.
> If it's digital, it will not do that.
> Denon says that I need to connect a separate analog audio signal to its
> input for that audio to go to the second TV.
> Can I configure mythtv to downsample AC3/DTS to stereo and play AC3 on its
> digital output like it does now _and_ analog downsampled audio to on its
> analog out?
> If not, I take it alsa can do that, but I've had very little luck with alsa
> configs in the past. Do you have a pointer to a working alsa config that
> will both
> 1) convert analog audio to digital and send both analog out and digital out
> 2) downconvert digital audio and send both the analog and original digital
>    signal?
> Thanks,
> Marc

I have been trying to do this for some time.  Problem with ALSA is that 
as far as I can tell the wiki that tells you how to do what you want 
doesn't work.  And even if it did, ALSA does a poor job of creating the 
spdif output.  Seems like it decodes and then encodes and that is 
probably not what you wanted.

I have a HDA chip and I know it could do this if the driver allows it.  
I have asked for some help in identifying the driver and its 
documentation but no luck so far.

What I ended up doing is using one of these: 
which you may be able to see is offered for under $20 on ebay.  I am 
feeding the spdif signal to it and setting it to 2.0 so it will take any 
spdif input (even 5.1) and properly convert it to 2 channel.  I will 
somehow take the signal and send it to my Rx for the surround system.

This may be a good solution for you as well.  It is cheap enough and 
this little box works well.


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