[mythtv] AC3 playback mangled until timestretch activated

[Yeechang Lee]

Matt W <mwood23 at gmail.com> says:
> That is, I get long audio dropouts on the primary AC3 audio stream
> -until- I fiddle with timestretch.  Then suddenly everything sounds
> fine, and I can get true DD via AC3 passthrough.  I can even change
> the timestretch back to 1.0x and things continue to run fine.

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.

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