[mythtv-users] ac3 passthrough problems

[Jason Sharpe]

 On Sep 22, 2006, at 5:31 AM, Thomas B�rkel wrote:
>
> > HI!
> >
> > Scott wrote:
> >
> >> Audio output device:
> >> ALSA:iec958:CARD=0,AES0=0x6,AES1=0x82,AES2=0x0,AES3=0x2
> >> Passthrough output device: Default
> >> Enable AC3 to SPDIF passthrough: [checked]
> >> Enable DTS to SPDIF passthrough: [checked]
> >> Aggressive Sound card Buffering: [not checked]
> >> Use internal volume controls: [not checked]
> >
> > It is funny, that this actually works, because with these setting,
> > MythTV uses the "Default" device for AC3, not the one with the hex
> > codes.
>
> Yes. But, my understanding of the "Passthrough output device" is that
> if it is set to "Default" (case sensitive) then it simply refers to
> the device defined by "Audio output device". This can be confirmed by
> running with mythtvfrontend -v audio > audio.debug.txt and looking at
> the device MythTV opens with ALSA.
>
> So you're correct that mythtv uses the "Passthrough output device"
> when AC3/DTS passthrough is enabled. However, setting "Passthrough
> output device" to "Default" is a special case that tells MythTV to
> use the "Audio output device". Using the HOWTO asoundrc file the
> following alternative setup should work as well:
>
> Audio output device:  ALSA:digital-dmix
> Passthrough output device:
> ALSA:iec958:CARD=0,AES0=0x6,AES1=0x82,AES2=0x0,AES3=0x2
> Enable AC3 to SPDIF passthrough: [checked]
> Enable DTS to SPDIF passthrough: [checked]
> Aggressive Sound card Buffering: [not checked]
> Use internal volume controls: [not checked]
>
> This config would be useful if MythTV was able to detect and route
> AC3/DTS sound through the "Passthrough output device" only as needed.
> For example, if in MythMusic sound would not be 48kHz AC3 format and
> get routed via the "Audio output device". During OTA ATSC playback
> where AC3 formats are present MythTV would route sound via the
> "Passthrough output device" instead.
>
> Of course, I have no idea if MythTV actually works this way. I'm just
> saying, based on the definition of the two fields that it would be
> nice if it MythTV could work this way! :)
>
> --
> Scott



Wow! Scott, Thank you!

I use optical as well for all of my sound out of my myth frontend and for
over the past year with .18, .19, and now .20 I have never been able to pass
through DD or DTS properly to the receiver.

The receiver would switch to DD mode when I tried different settings and
played an OTA HD recording, but I would get no sound. Then If I played
something recorded from my PVR-250 it would switch back to PCM and play
fine. Going to an OTA HD recording again would send the receiver back to DD
mode but silent.

I have tried probly 7 or 8 times over the past year to try to get this work
with every different .asoundrc config file possible without success.

I have an Intel HD on MOBO sound chip as well, however my aplay -l reports
CMIXXXX instead of ALCXXXX (sorry not at home so I don't have everything
exactly).

So just for kicks last night I started tinkering with it again with no
success and found this discussion. I deleted my /etc/asound.conf and made
sure I didn't have a ~/.asoundrc file and used the one from the Wiki to
start fresh. And I still couldn't get it to work.

On a whim and last resort last night I tried your string of
ALSA:iec958:CARD=0,AES0=0x6,AES1=0x82,AES2=0x0,AES3=0x2 in
the passthrough device and HD recordings played perfectly in DD! For the
first time EVER!

So the settings I have are:

Audio output device:  ALSA:default
Passthrough output device:
ALSA:iec958:CARD=0,AES0=0x6,AES1=0x82,AES2=0x0,AES3=0x2

Enable AC3 to SPDIF passthrough: [checked]
Enable DTS to SPDIF passthrough: [checked]
Aggressive Sound card Buffering: [not checked]
Use internal volume controls: [not checked]

This way PCM sound (from my PVR-250) plays using the default Alsa device and
DD is passed through to the string.

I can't believe after all of this I get true DD now from HD. It is like I
just started using Myth again... I am that giddy!

Also upgraded the backend and frontend from .20 to .20.2 and it fixed alot
of the other misc issues I was having. (Preview on recording list was
incorrect colors, fast forward and rewind would freeze after 5 secs or so
and then it would jump back to the original starting point, etc)

Overall .20 is a great improvement!

Thanks everyone!

Jason
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