[mythtv-users] ac3 passthrough problems

Michael T. Dean mtdean at thirdcontact.com
Sat Sep 23 18:02:16 UTC 2006

On 09/23/06 11:36, Thomas Börkel wrote:

>Michael T. Dean wrote:
>>Actually, it looks like MythTV completely ignores the Placebo--I mean 
>>Passthrough output device. ;)
>>(The only occurrence of "PassThroughOutputDevice" in 
>>myth{tv,plugins,themes} is in the settings page.)
>That's strange, because it actually works for me, as intended.
>I have no .asoundrc. I have configured ALSA:default (which is analog in 
>Alsa 1.06) as normal device and ALSA:spdif as passthrough device.
>Now, when I have NOT checked AC3 passthrough and play a AC3 5.1 
>recording, I get only Dolby Surround on my receiver. And I get analog 
>sound on my TV (using soundcard's analog output), too.
>When I check AC3 passthrough and play AC3 5.1, then I get Dolby Digital 
>5.1 on my receiver, but silence on my TV.
>When I play MP2 sound, then the AC3 passthrough switch does not change 
>anything. I always get Dolby Surround on my receiver and sound on my TV.
>So, if the passthrough device is being ignored by Myth, then it must use 
>ALSA:spdif by it's own choice.

I'm talking about

Passthrough output device
Audio output device to use for AC3 and DTS passthrough. Default is the 
same as Audio output device. This value is currently only used with ALSA 
sound output.


Enable AC3 to SPDIF passthrough
Enable sending AC3 audio directly to your sound card's SPDIF output, on 
sources which contain AC3 soundtracks (usually digital TV).  Requires 
that the audio output device be set to something suitable.

(nor the DTS equivalent).

Basically, if the setting is being ignored, it means that you always use 
the exact same (*nix) output device (not necessarily the same as a 
physical output device) whether playing back AC-3 or not.  How your 
audio drivers respond to that, though, is another matter entirely...  :)


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