[mythtv-users] AC3 passthrough still doesn't work.

Kevin Kuphal kuphal at dls.net
Sun Oct 24 16:03:23 UTC 2004

Bo Najdrovsky wrote:

> Well, I've made quite a bit of progress on my HD2000 based MythTV box, 
> but there is one last remaining nagging issue, and that's the fact 
> that the AC3 passthrough does not work in mythfrontend.  I'm able to 
> play the recorded .nuv files with mplayer, and the AC3 passthrough 
> works fine with that program when I use the command line option -ao 
> alsa:device=spdif    This fact confirmed for me that my hardware is 
> not at fault, but the bug must be in Myth.  I went and recompiled 
> MythTV 0.16 to make sure that ALSA output is enabled, restarted 
> everything and put ALSA:spdif into the audio device field in front end 
> configuration, but the results are the same as with OSS... I hear 
> about quarter second of audio, and then silence.  I'm guessing that 
> perhaps mythfrontend isn't setting up the SPDIF port correctly.  Any 
> ideas?
AC3 passthrough does not mean that Myth will output on the SPDIF 
connector.  It means that if your content has AC3 audio then it will be 
passed untouched to the audio device.  If your recorded or live content 
has anything but AC3 source material you will get only garbage.  To get 
output on the SPDIF connector, you need only configure ALSA OSS 
emulation to output everything to it or, as you noted, use the 
ALSA:spdif feature in the audio field.

 Secondly, the ALSA support in Myth is somewhat in flux and also works 
best with the 1.0.5a version of ALSA when compiled against it.  The CVS 
version has some fixes and also some patches are being worked on that 
revamp the audio portion of Myth with better ALSA support.  I don't know 
if either of these will help but I wanted to make sure you were on the 
right track and understood what the current status is.


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