[mythtv-users] LipSync Issues with HDMI and 0.22

Jurgen Kramer gtmkramer at xs4all.nl
Fri May 7 07:48:40 UTC 2010

On Thu, 2010-05-06 at 02:03 +1000, Jean-Yves Avenard wrote:
> Hi
> On 5 May 2010 21:16, Jurgen Kramer <gtmkramer at xs4all.nl> wrote:
> > I have the same problem when I switch my TV to 24Hz for 24fps films when
> > playing with mplayer. What seems to help (workaround) is that when I do
> > a fastforward while playing and then return to the original playing
> > position with a rewind the lag is gone. I guess this is a caching issue
> > of some sort.
> >
> > Nb when I play 24fps films with the TV still on 50Hz there are no
> > lipsync issues.
> The problem is that the refresh rate is never a perfect static value,
> and there will always be syncing issues between the TV and the video
> card.
> When your TV is set at 24Hz, the decoding + playback doesn't have much
> latency to play with. If the video is playing slightly too fast, it
> has to drop frames , if it's playing too slow it needs to seek
> forward.
> Calculating the proper timestamp to keep perfect AVSync becomes complicated.
> That's why you will usually notice in the logs that myth is suddenly
> playing twice faster to catch up or dropping frames.
> When your TV is set at 50Hz, those issues do not occur and it's much
> easier to keep thing working properly.
> There is a patch somewhere for mplayer that improves things. I would
> have thought it made it to mplayer by now. Have you tried a recent
> mplayer ?

Not yet, I will probably hold of until I upgrade my frontend to F13 and
MythTV 0.23.
Currently using mplayer SVN-r29800-4.4.2 from rpmfusion, mplayer svn is
at r31139 so that's fairly old.

> As for MythTV and AVSync, under some circumstances (especially with
> timestretch active), there were errors in the timecode calculations
> and there is work currently underway to improve the algorithm used for
> AV-Sync.
> I would expect that it won't be too long before this work gets in,
> hopefully by 0.24
> Jean-Yves
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