[mythtv-users] stereo+AC3/DTS sound to both analog+digital outputs

[Petr Stehlik]

Hi,

first the goal I'd like to achieve: to lower the power bill by not
running my 5.1 receiver when not necessary (an overkill for poor stereo
sounds of most recordings). Also the receiver eats 40W when idle and
they often forget to turn it off after watching something.

My setup: MythTV 0.21 with analog stereo output wired to TV and digital
output wired to the receiver. The TV has fairly good speakers so it
would be OK to use just that (and keeping the 5.1 receiver turned off)
for most recordings, videos and DVDs. But often I'd like to listen to
the sound in the full 5.1 digital quality so if I turn the receiver on
I'd like it to play all MythTV sounds.

MythTV allows to configure AC3/DTS pass-through. With the pass-through
disabled and no ALSA magic enabled all sound sources (stereo, AC3, DTS)
play on the analog output only. I miss the sound on the digital output
here.

Now if I enable the AC3/DTS pass-through in MythTV then stereo sound
goes to analog output _only_ (=plays on the TV) while AC3/DTS goes to
digital output _only_ (plays on the receiver only). This is the worst
situation for WAF, believe me ;)

To solve this problem I have added an ALSA magic with a small .asoundrc
that basically routes everything to the digital output (I guess, I am
not ALSA expert):

pcm.!default {
	type plug
	slave {
		pcm "spdif"
		rate 48000
		format S16_LE
	}
}

With this .asoundrc in place _everything_ plays on the digital output
only - I miss the sound on the analog output (= in the TV).

I am not sure if this is just a configuration issue in MythTV or if it
can be "fixed" by an advanced ALSA setup or if I'd need some internal
changes in MythTV. My current setup is the following:

Sound device: ALSA:default
Pass-through device: ALSA:iec958:{AES0 0x02}
Upmix: stereo passive

I'd like MythTV to work like if the AC3/DTS is _disabled_, i.e. to play
even the AC3/DTS sounds on the analog output, yet _at the same time_ to
pass-through all AC3/DTS sounds unmodified to the digital output. Plus
I'd need to configure ALSA to watch the analog+digital outputs and if
there is something on the analog but not on the digital one then to
_copy_ the analog to the digital output so even the poor stereo is
available on the digital output. All this happening automagically
without user fiddling with config stuff.

Sounds complicated? I simply wants MythTV to play all sounds on both
analog+digital outputs without unnecessary down/upmixing (AC3/DTS passed
through unmodified).

Any suggestions, please?

Thanks

Petr