[mythtv-users] Simultaneous analogue (analog) and S/PDIF output

[Alex Butcher]

Hi Jean-Yves -

On Wed, 12 Jan 2011, Jean-Yves Avenard wrote:

> On 12 January 2011 07:59, Alex Butcher <mythlist at assursys.co.uk> wrote:
>> That would be perfectly acceptable.
>
> I think we misunderstood each other. I have been consistently
> referring to the numerous other threads discussed this in the past 2
> weeks where I have repeated several times the procedure on how to do
> so.

I'm sorry; I promise you I've looked, but haven't found anything directly
relevent. I think I know the threads you describe, but they aren't as
detailed as I need.

> So once again:
> Your default output device needs to be a device that you crafted with
> the ALSA configuration ; you create a mixer device that will send
> audio to both analog and digital device.

OK, presumably I've got that with my current .asoundrc, as it works with
other ALSA apps and with mythfrontend now that I've disabled PassThru.
That's the easy part. :-)

> Then you set the passthrough override to ALSA:iec958:AES0=6, and check
> the StereoPCM flag, and do not enable the 5.1 stereo upmixer..

Regarding the upmixer, it's already disabled:

| AudioDefaultUpmix | 0    | xxxxxxxxxxxxxxxxxxxxxxx |
| AudioUpmixType    | 0    | xxxxxxxxxxxxxxxxxxxxxxx |
| MusicDefaultUpmix | 0    | xxxxxxxxxxxxxxxxxxxxxxx |

A further complication is that I don't think the audio settings page is
displaying properly on my system. I don't know whether that's an issue with
the build from rpmfusion that I'm using, or whether it's because there are
too many settings to squeeze onto my display (1024x576, with mythfrontend
using 944x557 to avoid parts of the GUI being in the overscan area). For a
start, the 'Device Capabilities' box is squashed to nothing. It looks just
like <http://www.gregandeva.net/mythfrontend.png> reported in
<http://www.gossamer-threads.com/lists/mythtv/users/443270#443270>. I'm
running a more recent 0.24-fixes though:

$ rpm -q --changelog mythtv
[...]
* Mon Nov 22 2010 Jarod Wilson <jarod at wilsonet.com> 0.24-2
- Update to release-0-24-fixes, svn revision 27317
- Add preview image fixup patch from ticket #9256
- Add alsa passthru device patches from trunk r27306 and r27307
[...]

There's no StereoPCM flag in my GUI. Is the StereoPCM flag you describe the
MultiChannelPCM row?  If so, that's currently:

| MultiChannelPCM | 0    | xxxxxxxxxxxxxxxxxxxxxxx |

The schema documentation at <http://www.mythtv.org/wiki/Settings_table>
seems to be out-of-date regarding this.

Presumably the StereoPCM GUI element is the inversion of the MultiChannelPCM
row value.

If I understand you and mythtv-0.24/libs/libmyth/audiooutputsettings.cpp
correctly, to summarise your settings for non-upmixed stereo over analogue +
S/PDIF, but passthru for AC3 and DTS (with the caveat that analogue channel
will need to be muted), I think I need to make these settings:

AudioOutputDevice=ALSA:default
MixerDevice=ALSA:default
MixerControl=PCM
MasterMixerVolume=per preferences
AudioDefaultUpmix=0
AudioUpmixType=0
MusicDefaultUpmix=0
AC3PassThru=1
DTSPassThru=1
AdvancedAudioSettings=1

These I'm less sure about:
MaxChannels=2 ???
PassThruDeviceOverride=0 ???
PassThruDevice='ALSA:iec958:AES0=6' or 'ALSA:iec958:{ AES0 0x06 }' ???
MultiChannelPCM=0 ???

I hope you'll forgive me for being persistent; as well as solving my
immediate problem I'm trying to make this thread something of a canonical
explanation of how MythTV handles analogue, S/PDIF, and so on so that people
with problems can refer to it to debug their problems too (regardless of
what the GUI reports; we've all seen incidents where the settings GUIs
report differ from the settings that are actually being /used/).  I'll wiki
it later, even.

> Stereo will be sent to both analog and digital simultaneously that way.
>
> AC3, DTS and other multichannels audio will be sent to the passthrough
> device only.
>
> Now, if your passthrough device is hdmi, and it is connected to a
> multi-channels capable device ; then use that alsa crafted mixer for
> everything. Do not use passthrough override, do not check AC3 or DTS
> and everything will be sent as multi-channels LPCM when required, you
> can then use the upmixer too

I'll bear that in mind if/when I pick up a display with HDMI. In the
meantime, it's good reference for anyone else reading who's already in that
situation though.

>> *ahem* Are you quite sure it should work as you describe?
> of course I'm sure..
>
> I wrote that code.... It's like asking if I'm sure if the shoes I'm
> wearing are yellow

:-)

I'm aware of your status as author of many of these bits (and the original
VDPAU stuff). My comment was really intended as "Are you sure it /worked/ as
you describe /as of 21 November 2010/, rather than -trunk or the /current/
0.24-fixes'. :-)

> (And one more thing, there's no point hacking through the database, I
> only ever use the settings, the mysql values you are referring to are
> meaningless to me)

But my UI doesn't show some of the settings you describe or at least, not
with the labels you give them.  I gather others have reported the same
problem with screenshots (I think you were in the thread).

> JY

Many thanks,
Alex