[mythtv-users] ac3 passthrough results in accelerated video
Michael T. Dean
mtdean at thirdcontact.com
Thu May 29 16:15:44 UTC 2008
On 05/29/2008 11:30 AM, scram69 wrote:
> Recently upgraded to 0.21 so I could finally get ac3 passthrough
> working on my osx frontend. When it works, it's great - however...
> Just about every other time I start to watch a recording, the
> playback, both video and sound, is accelerated, as if I were watching
> using 2x-3x timestretch or fast forward. (I bring up the time stretch
> menu, and it indicates 1.0x) If I uncheck ac3 passthrough in the
> Setup>General menu, the problem goes away.
> Unfortunately, the frontend log output is _exactly_ the same when I
> see this accelerated playback as when I do not.
> There have been a number of posts about ac3 passthrough in 0.21, but
> in searching, I haven't come across this issue. Has anyone else
> experienced this?
Does it always happen on any given recording or are you saying that on a
particular recording, you'll sometimes see it play incorrectly and
sometimes see it play correctly?
If it always happens on a given recording, it's just a matter of your
broadcaster choosing to use 32kHz AC-3, which the vast majority of
computer-based sound cards cannot handle (they play it as 48kHz, thus
the "timestrech"--which is actually more of a "chipmunking" as there
shouldn't be pitch correction). Myth just keeps the video in sync with
the audio as passthrough means that adjusting the audio stream is
Oh, and if you enable timestretch--even to 1.05x or something--it will
"make it work" by disabling passthrough. TTBOMK, even if you then go
back to 1.0x, it will still "work" (as Myth won't re-enable passthrough
unless you exit playback and restart playback).
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