[mythtv-users] ac3 passthrough problems

Michael T. Dean mtdean at thirdcontact.com
Fri Sep 22 04:42:21 UTC 2006

On 09/21/06 22:28, Scott wrote:

>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
>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 don't know the specifics of MPlayer's "-vfm hwac3", but basically, yes 
it should do exactly that.

>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.
Because informing the receiver of the type of sound data is the 
responsibility of the application not of the driver...


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