[mythtv-users] AC3 Passthrough issues

[Matt]

On 3/12/06, Matt <skd5aner at gmail.com> wrote:
> On 3/12/06, Michael T. Dean <mtdean at thirdcontact.com> wrote:
> > On 03/12/2006 08:33 PM, Matt wrote:
> > >   I've been searching around, and I can't quite find someone having
> > > the same issue I'm having.  I've got alsa with SPDIF passthrough.
> > > It's been working great for analog shows,
> >
> > Note that you cannot have "passthrough" with analog.  Passthrough is
> > used to pass an AC-3/DTS stream directly through Myth to the receiver.
> > For analog TV, Myth outputs PCM data, instead, because there is no
> > AC-3/DTS stream to pass through.
>
> Right, I understand.  I guess I meant that it worked via spdif optical
> out, not necessarily "digital sound" passthrough for the receiver to
> decode.
>
> >
> > >  and I just installed my
> > > digital cards this weekend.  I recorded an HD broadcast today, Nascar,
> > > and when I started to play it, all I heard was the cars.  I didn't
> > > hear announcers, sound effects... nothing besides "VROOOOM".  So... I
> > > figured... interesting.
> > >
> > > I went into the menu and saw that the first audio channel said AC3
> > > 5.1.  So, I figured "This is only playing a few of the channels".
> > > However, it happens on all the HD stations.  I've tried many of the
> > > suggestions I found for passthrough, but none of them worked.  I'd
> > > either get no sound, or the same sound.
> > >
> > > The interesting thing is, that when I played analog, my receiver would
> > > show "PCM 48K" and play just fine.  When I played the digital, nothing
> > > showed up on the receiver screen and it just played the sounds.  When
> > > commercials came up, you could hear a little more, but you could tell
> > > much was missing.
> > >
> > > Any clues?
> > >
> > > Here's my .asoundrc file:
> > >
> > > ## Uncomment the following to use mixed digital by default
> > >   slave.pcm "dmix-digital"
> > >
> >
> > Don't use dmix.  Change your default to "digital" (uncomment the
> > "digital-hw" line and comment the "dmix-digital" line).
> >
>
> Alright...  I did that... funny thing happened:
> 1) watched the show, heard voices, and there was seperation of
> channels.  However, the receiver did not say it was decoding
> anything.. YAY?  No...
> 2) Closed the show... re-opened... no sound
> 3) Closed it again... waited a few seconds, reopened... same thing as
> before... only the sound of the cars, no announcers.  I also have
> westwing.  I could hear the dramtic music, but no talking.  It sounds
> like I'm getting L/R but no center or rear.
>
> Also... I have myth set to ALSA:digital and the mixer set to "digital"
> and the drop down next to the set to PCM.
>
> I can still verify that analog shows get sent to the receiver as PCM.
>
> What now?
>
> Thanks!
> Matt
>

Well, I found out another thing...

 - The receiver was set to AFD (Auto Format Decode).  It was able to
instantly identify the PCM stuff as two channel, but it never detects
the AC3 passthrough as true AC3.  I had to manually set it to
"surround" and then I got the channels.  HOWEVER, it still doesn't say
that it's truly decoding an AC3 signal.

I think this might be a bug in the format of the signal that myth is
passing.  How can we troubleshoot this?

Thanks!
Matt