[mythtv-users] audio issue with 6 channel TV output

Barry Martin barry3martin at gmail.com
Tue Nov 8 01:39:05 UTC 2022

Hello Matthias!

> Hello Paul, Barry,
> not adding anything helful I am afraid, but maybe related? Recently I 
> observed the problem tha occasionally, the audio of my recordings gets 
> tainted... I think the center channel in the surround audio track gets 
> lost, yesterday I had an example, some sound but almost no voices.I 
> switched the frontend audio to hdmi/2.1, same, then in the playback, I 
> switched from the surround track (ac3 I think) to stereo and the 
> voices were back.

Here during playback of some DVDs (old school! <joke>) we have noticed 
sometimes the surround sound is not properly detected so only plays 2CH 
(front channels).  Sometimes a power cycle brings it back, sometimes 
not.  While this has nothing to do with MythTV it seems to indicate 
sometimes the signal isn't correctly determined.  (Will see what happens 
when I add a Frontend after the remodeling.)

> It is just some minutes, not the whole recording.

Possibly nothing but I am wondering if when the surround sound channels 
are lost if there is a problem with Closed Captioning? Here have noticed 
some CC 'spelling' is really bad: parts of words are missing or 
duplicated.  Something like "the quick brown fox" would be displayed as 
"the quin bro foxox" ==> 'quick' and 'brown' being smooched together, 
the 'ox' of 'fox' being repeated.  Thinking perhaps a slight corruption 
of the programme -- thinking if you loose your surround sound plus a 
corruption of the Closed Captioning text then perhaps is due to a 
problem in the recording.  (I'm only barely familiar with ATSC format 
here in the U.S.; guessing you are in the EU and so PAL -- may not be 
the same method of CC encoding.)

> This has happened several times recently, but never before that. I 
> suspected the problem in the programming or recording, drivers...??? 
> But not in myth. I guess I should try to reproduce playing the file 
> with with vlc.

Out of curiosity if you replay the segment with missing surround sound 
audio does the same thing occur?  Might indicate if the problem is in 
the recording or was possibly due to a heavier load on a processor at 
the time.  I'll admit this is a guess. Comparison via VLC is also a good 
thought: at least would help determine if the problem was in the 
recording or the playback process.

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