[mythtv] AVSync Problem on entering recorded playback

Stephen Williams stephen.gw at gmail.com
Tue Mar 28 21:45:40 UTC 2006


On 3/28/06, Stephen Williams <stephen.gw at gmail.com> wrote:
> I'm only seeing this with recorded content, live TV works fine. Also
> this is only with SD content, not pushing the box at all (less than
> 50% CPU usage and no prepuffering pauses).
>
> Haven't noticed audio/video slowdown then speed up again. Not sure why
> you'd be seeing that, the video speed should be constant when using
> video as timebase unless AV get more than 3 frames out of sync.
>
> It's definitely a problem with MythTV directly, from the debugging
> i've done the AVSync code is clearly failing. Done a bit of code
> review of that area and there's quite a lot of undocumented 'magic'
> going on, especially with the audio 'warpfactor' calculation. I'll
> keep digging and see if it can't be improved.
>
> Stephen

Okay, i've been making some progress on this now. Disabling the
dropping of frames / doubling of frame times and allowing the AVSync
code to settle down (takes a few minutes to stabilise) it has become
apparent that on initial entry to recorded playback it is trying the
play the video at 30fps (note that this is PAL content at 25fps).

After pausing / unpausing it then starts to play the content correctly at 25fps.

Now for the million dollar question, why are we initially defaulting to 30fps?

Stephen


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