[mythtv] AC3 playback mangled until timestretch activated

Matt W mwood23 at gmail.com
Thu Feb 11 20:30:20 UTC 2010

> Your description resembles, and your log excerpts somewhat resemble,
> what I reported at #8030. I hadn't known about the timestretch
> workaround but indeed that does work for me.
> As noted in the ticket, I'm pretty sure the issue has something to do
> with the trunk audio code not handling properly the transition between
> a non-AC3 and a AC3 audio track. Applying your observations to my
> experiences with other afflicted recordings, another factor appears to
> be the presence of a non-AC3 track, like so:
>     0:15----0:30----0:45
> #1   Stereo--AC3---------
> #2   None----Stereo------
> The Stereo track (upmixed to Dolby Digital) on #1 plays properly until
> it swaps to an AC3 track, with the Stereo track moving to the
> now-existing #2. This confuses the audio code.

Yeechang, that is interesting.  In my case, the playback shows all
three streams as AC3 encoded, but indeed, when I switch the playback
to either of the two other streams (which btw, are not French or
Spanish but a descriptive audio channel, and normal stereo channel),
my amp switches back to the default Dolby PL II that I have set up.
When I switch between the DD stream and one of the others, and then
back to DD, I still have sync/dropout issues.  Only playing with
timestretch seems to "tickle" the playback into properly handling the

Should I add my comments to your open ticket? I've only done one of
those bug reports before so I'm not sure about the etiquette!  :-)


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