[mythtv] AC3 playback mangled until timestretch activated

[Yeechang Lee]

I wrote:
> 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

Further support for this theory came from another recording of
_The Tonight Show with Conan O'Brien_ (in reruns) tonight with proper
audio playback due, I believe, to only having one audio track:

     0:15----0:30----0:45
#1   Stereo--AC3---------

This is in contrast to the aforementioned problematic _Tonight_
recording:

     0:15----0:30----0:45
#1   Stereo--AC3---------
#2   None----Stereo------

So it's not transitioning from a non-AC3 to AC3 audio that's the
problem; it's doing so with another audio track in the recording. I am
unsure on what would happen if track #2 existed from the start of the
recording like #1.

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