[mythtv-users] ac3 passthrough problems

Scott list-mythtv at bluecamel.eml.cc
Fri Sep 22 02:28:11 UTC 2006

On Sep 21, 2006, at 5:00 PM, Michael T. Dean wrote:

> On 09/21/06 15:36, Scott wrote:
>>  On Sep 21, 2006, at 2:17 AM, Thomas Börkel wrote:
>>> Apparently, Myth sends raw AC3 data to Alsa and Alsa does not
>>> switch your receiver to DD.
>>  Not necessarily. It's perfectly possible to send analog format
>>  signals out the spdif and for the receiver to decode them.
> It is not the responsibility of the underlying driver to tell the
> receiver to switch modes when the application changes audio
> formats--it's the application's responsibility.  Some receivers are
> better at "auto-detecting" formats than others.  Some sound cards are
> better at creating specification-compliant data streams which enhance
> the receiver's ability to auto-detect.
> Myth doesn't yet do well at informing the receiver of the audio stream
> type (because all previous attempts to add functionality to do so have
> broken more systems than they've fixed--and not just because of bad
> configurations).

Mike, are you implying, or saying, that when I use mplayer -vfm hwac3  
to pass data to my spdif, that mplayer is putting some sort of header  
on the stream to inform my A/V receiver to switch to the proper mode?  
I really don't think you're saying this but I want to confirm.

Going back to the AC3 sound saga at hand, I plan to update to alsa  
1.0.13-rcX and see if it makes a difference.  I suspect it will not  
since it appears only MythTV is having an issue. From there, if that  
fails I'll try disabling on board sound and seeing if MythTV and a  
Audiogy 2 ZS do any better. I hate to that as the "extra" pci slot  
was going to be used for a future tuner.


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