[mythtv] Live playback / Timestretch

[Doug Larrick]

Neil Whelchel wrote:
> Hello,
> I was just wondering if anyone was working on or planning to work on a
> patch to use timestretch to keep live tv playback in sync. IE If playing
> live tv and the current playback position is within 30 seconds of real
> time, use timestretch to keep it there. If not, I would like to give it a
> shot..
>
> The thinking behind this is that in real use there always ends up being a
> slight offset between record and playback speed. (Seems to mostly be
> caused by poor audio hardware.) Some of my front end machines play faster
> and run out of data causing a brief pause (very annoying), other ones are
> a bit slower and fall behind (not as bad, but I personally don't like it
> either). So, if the front end sees that the current playback position is
> less than say 45 seconds behind current time, simply change the
> timestretch value a very small amount plus or minus to keep it closer to
> ~20 seconds.
>
> Any thoughts, or suggestions?

Sounds like a good idea to me.  You should look at the code for "use
video for timebase;" in fact, it might make sense to just use
timestretch if this option is enabled, rather than the current code
which speeds up/slows down the audio.  Neither approach works for AC3
passthrough, so no loss there; the only issue I can see is if
timestretch takes more CPU than the existing implementation.

-Doug
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