[mythtv] AVSync Problem on entering recorded playback

Mark Buechler mark.buechler at gmail.com
Tue Mar 28 20:54:20 UTC 2006


I noticed you're using video as timebase.. Using that with 720p content,
does your audio/video slowdown then speed up again every once in awhile?

- Mark.

On 3/28/06, Steven Adeff <adeffs.mythtv at gmail.com> wrote:
>
> On 3/28/06, Mark Buechler <mark.buechler at gmail.com> wrote:
> > On 3/28/06, Stephen Williams <stephen.gw at gmail.com> wrote:
> > > I'm seeing stuttering playback on entry to recorded program playback
> > > (DVB source), a pause/unpause clears this up.
> > >
> > > Having performed some debugging I have determined that the AVSync code
> > > is never managing to get a sync. The following excerpt is from the
> > > frontend log with "-v playback":
> > >
>
> <snip>
>
> > > We continually get the above "doubling video frame interval." messages
> > > until playback has been paused / unpaused. It appears that the system
> > > is never able to sync in the case where audio is ahead of video.
> > >
> > > Having added more debugging to NuppelVideoPlayer it appears that
> > > something it deliberately 'correcting' for the doubled video frame
> > > interval used to regain sync. This has been determined by timestamping
> > > calls to NuppelVideoPlayer::DisplayNormalFrame, the
> > results are as
> > > follows:
> > >
> > > 1. During normal (correctly AVSynced playback)
> > > NuppelVideoPlayer::DisplayNormalFrame is called at a very
> > regular rate
> > > every 40ms (25fps).
> > > 2. When attempting to regain AVSync by doubling the video frame
> > > interval this increases to 60ms (this is expected and temporarily
> > > brings the AVSync to within 3 frames).
> > > 3. However, as soon as we stop doubling the video frame interval this
> > > timing is reduced to 20ms, it appears that something is trying to
> > > compensate for the 60ms frames.
> > >
> > > I'm looking for some further guidance on how to debug this issue. Is
> > > anybody able to tell me what is controlling the rate at which
> > > NuppelVideoPlayer::DisplayNormalFrame is called during
> > normal
> > > playback, i.e. what mechanism is causing those 20ms frames that are so
> > > effectively counteracting the attempt to gain AVSync?
> > >
> > > Some further system information is supplied below in case it is
> required:
> > > - Using OpenGL Vsync to a PAL TV (using an interlaced modeline).
> > > - I've tried with and without OpenGL Vsync, there is no difference.
> > > - Running 0.19-Fixes branch.
> > >
> > > If I can provide any more data then please let me know.
> > >
> > > Thanks in advance,
> > > Stephen
> >
> >
> > Question, are you seeing this ONLY with recordings? A few people have
> > reported seeing this with LiveTV until they pause/unpause. I have the
> same
> > issue but mine seems to loose sync at times with 720p content and
> eventually
> > regains it. I'm wondering if all of these could be symptoms of the same
> > problem.
> >
> > - Mark.
>
> I offer this up to help diagnose the problem as I don't think it is an
> issue with MythTV directly....
>
> I haven't noticed any audio sync issues on my machine with 1080i or
> 720p (I am not using XvMC). I do notice a 1-3sec stutter when starting
> playback of recordings, and sometimes after pausing. For live tv the
> stutter lasts a little longer usually and sometimes after changing
> channels it looks like its dropping frames but the audio remains in
> sync. Pausing and unpausing clears all these issues up (I just wait
> for the 1-3sec stutter period since its easier and goes away on its
> own).
>
> I've been running my own builds off the fixes branch.
> --
> Steve
> _______________________________________________
> mythtv-dev mailing list
> mythtv-dev at mythtv.org
> http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mythtv.org/pipermail/mythtv-dev/attachments/20060328/d8a4ccf1/attachment.htm 


More information about the mythtv-dev mailing list