[mythtv-users] ac3 Issues/Questions

Peter Schachte schachte at csse.unimelb.edu.au
Thu Jan 25 01:35:08 UTC 2007

[Sorry to users of threaded mail readers; this is a resend of a bounced
message, and I've lost the References: line.]

>> I've been using spdif out with no problems when not using AC3.  When I
>> set the switch in the setup to pass ac3 a few things happen.  First, I
>> get a consistent -300ms sync issue and secondly, when I switch to just
>> listening through my tv rather then my spdif out, I get the digital
>> static noise through the TV.  I can fix that by changing the audio
>> source in the menu but...

Not sure if this will help, but you might try setting the passthrough device to
ALSA:digital (or ALSA:spdif, or whatever you use for SPDIF out), rather than
Default.  I found this got rid of the horrible noise on the analog output.  It
also got rid of all sound to the analog output when playing a DVD with surround
sound.  I have yet to find a way to get normal analog output when playing a
surround sound encoded DVD with AC3 passthrough selected.

>> 1) Is there a way to set the -300ms sync in the system settings
>> somewhere?

I haven't seen a sync problem.

>> 2) Is there a way to set the default audio to non-ac3 and perhaps set a
>> button on my remote for turning on ac3?

You could probably write a little script to hack the database to toggle AC3
passthrough, and use irxevent to execute it when you hit a certain remote
button, but I don't know how often Myth checks the database for that config
setting, so it might not work very well.  You'd probably at least have to
restart the playback for the toggle to take effect.

If you use both digital and analog sound, you might want to read my posting
here with the subject "simultaneous analog and digital (SPDIF) audio output

Peter Schachte              One of the symptoms of an approaching nervous
schachte at cs.mu.OZ.AU        breakdown is the belief that one's work is
www.cs.mu.oz.au/~schachte/  terribly important.
Phone: +61 3 8344 1338          -- Bertrand Russell

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