[mythtv-users] 0.25 Major AV sync problems

Richard peper03 at yahoo.com
Mon Jul 23 18:26:00 UTC 2012

On 05/07/12 21:41, Richard wrote:
> On 19/06/12 06:24, Jean-Yves Avenard wrote:
>>> I'll upload a sample when I can figure out where to upload it to. 
>>> The things
>>> I see are common across all DVB-T broadcasts in NZ. No difference if I
>>> select AAC or AC3 audio on channels where this is possible. The problem
>>> seems to be something to do with audio PTS so I guess it's 
>>> independent of
>>> codec type.
>> it's bizarre that it's not something everyone would see
> I get the feeling it has several causes (whether individually or 
> together).
> I just had another play around and found turning off 'Separate video 
> modes for GUI and TV playback' seemed to cure it.  The resolution for 
> both GUI and Video output were both set to 1920x1080 with the frame 
> rate set to 'auto'.  I'd originally turned this setting on to handle 
> the one or two US DVDs I have but I noticed that although I'm in PAL 
> land, the GUI had a tendency to end up refreshing at 60Hz, which 
> causes the TV to go black for a second or two whilst it re-syncs.
> After turning it off and jumping backwards and forwards in a recording 
> that had been getting out of sync before, everything was fine.  Then I 
> turned it back on again and tried explicitly setting the frame rate to 
> 50Hz or 25Hz but that still gave me sync errors.  After I turned it 
> off again, I was *still* getting sync errors.
> Changing the deinterlace method from 'Temporal 2x' to 'Temporal 1x' 
> also fixed the problem (although it doesn't look quite as good).
> Then I tried running nvidia-settings and explicitly set the refresh 
> rate to 'Auto'.  Now I could set the deinterlace method back to 
> 'Temporal 2x' and not get sync errors.
> I see the ticket (10797) has been closed and marked as fixed although 
> I don't think it *is* fixed.  I think it may well be caused by several 
> conditions having to be present, but in one of several combinations.  
> You change one setting and think you've cured it and then something 
> else changes (perhaps due to restarting the system) and the problem is 
> back again.
> Regardless of all the different settings, *something* is stopping the 
> audio and video getting into sync after a jump.  They're in sync when 
> you first start playing and only get out of sync if you jump (whether 
> manually or because of a cut-point).  If you pause playback for a few 
> seconds and then unpause it, they're back in sync again and stay that 
> way until the next jump so it can't just be a case of 'the hardware 
> isn't up to this deinterlace method' or 'the audio buffers are too 
> low' or whatever.  If that were the case, the two streams should 
> either always be out of sync or possibly get progressively more out of 
> sync.
> I'll keep an eye on my system over the next few days.

Ok, since I turned off 'Separate video modes for GUI and TV playback', 
I've not had any sync problems.  I don't believe this particular feature 
is broken since even with it turned on, it's possible to get picture and 
audio in sync (via pause) but it's certainly helping to get the stars in 
alignment on my system so that the problem *can* occur.


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