[mythtv] AC3 playback mangled until timestretch activated

Yeechang Lee ylee at pobox.com
Sat Feb 13 21:25:43 UTC 2010

Matt W <mwood23 at gmail.com> says:
> hm interesting.  So is that a case of the broadcaster sending an AC3
> stream that contains 0 channels?

The OSD menu shows multiple tracks because there are multiple tracks
within the recording, if not necessarily at the beginning.

#1   Stereo--AC3---------
#2   None----Stereo------

"None" means there is no second audio track at all until the program
with two audio tracks begins.

> Yes it seems to be the multiple channel count that trips up my myth
> box.  That PBS broadcast that first alerted me to all of this had
> three AC3 streams, with a total of 10 active channels, total.

I don't believe that the total number of audio channels is relevant,
per se; only that multiple audio tracks exist *and* that not all of
them are present at the start of the recording.

Another interesting finding: The timestretch workaround works even at
the start of the affected recording, before the second audio track
(and consequent issue in playing the first, default, track) begins. In
other words, a quick hack that forces a timestretch change to, say,
1.05X, then back to 1.0X, when playback begins might work.

Again, this is an issue only with the trunk audio code, not with the
0.22 stock code.

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