[mythtv-users] 60hz too slow for NTSC + Bob deint?

Jesse Guardiani jesse at wingnet.net
Wed Apr 19 05:16:55 UTC 2006


On Tuesday 18 April 2006 8:28 am, Doug Larrick wrote:
> Jesse Guardiani wrote:
> > Hello,
> > 
> > Is 60hz just too slow for NTSC + Bob deint?
> > Or is something lying?
> > 
> > I get this when I try to play back NTSC video
> > on my LCD TV running 60hz:
> > 
> > 2006-04-16 22:54:19.226 OpenGLVideoSync: x,y -> 720, 450
> > 2006-04-16 22:54:20.944 NVP: Timed out waiting for free video buffers.
> > 2006-04-16 22:54:21.338 Using OpenGLVideoSync
> > 2006-04-16 22:54:21.338 Set video sync frame interval to 33366
> > 2006-04-16 22:54:21.338 Video sync method can't support double framerate
> > (refresh rate too low for bob deint)
> > 2006-04-16 22:54:21.339 Set video sync frame interval to 33366
> > 2006-04-16 22:54:21.342 Using deinterlace method bobdeint
> > 2006-04-16 22:54:21.354 Using audio as timebase
> > 2006-04-16 22:54:21.354 Video timing method: SGI OpenGL
> > 2006-04-16 22:54:21.354 Refresh rate: 16697, frame interval: 33366
> > 
> > 16697 > 33366 / 2 
> > 
> > And according to vsync.cpp, that's a problem.
> > I something lying, or are those numbers correct?
> >
> 
> Do you have a default timestretch factor turned on?  That can push the
> required refresh rate too high.
> 
> But actually, 16697 corresponds to 59.89 Hz vertical refresh... this is
> fractionally less than the 59.97 that you actually need.  Sounds like
> you need to play around with your modeline.

I realized tonight that I should have known the subject of this thread was 
incorrect from the start. I have 2 LCDs in the house. The first is an 
HDTV (1360x768) and the second is a computer monitor (1440x900). I 
realized that the first has been using a custom modeline since I installed 
it and I don't get this Bob error on that screen. So only the monitor was 
broken in this way, and yeah, I generated a new modeline for the monitor 
and that fixed it. Now I just get typical Bob behavior: It works under 
certain circumstances, and starts to break under others.

This particular machine is a network attached frontend. Bob starts up choppy
with lots of Prebuffering pauses in the logs, but if I switch to another 
virtual desktop for a second, then switch back everything smooths out and the
prebuffering pauses completely go away. Pausing and rew/ff causes the 
Prebuffering pauses to come back, but switching to another virtual desktop 
for a few seconds always solves the problem.

My primary machine, a combined frontend/backend (to which the above mentioned
frontend connects) can playback Bob just fine from the start. Rew/FF works 
without introducing Prebuffering pauses too. But Pause and channel changes
will cause the prebuffing pauses to start up. I don't have virtual desktops
on this frontend as it's dedicated to MythTV duty, so I can't say if switching
to another would help. Once the Prebuffing pauses start, there's nothing I
can do.

The hardware cards on these machines are a bit different. I'm running an AGP
6200 on the primary, and an AGP 5200 on the network attached frontend. I can't
know if some of the differences in behavior might be hardware related unless I
swap the cards and retest, which I probably won't do.

There's a rhyme or reason here. I'm convinced that Bob is doable and it's just
that some code somewhere is broken. I'll take another look at the code tomorrow
and see if I can spot anything out of place. However, I suspect someone more 
familiar with the playback code could probably make short work of this bug if
they could reliably reproduce it.


-- 
Jesse Guardiani
Programmer/Sys Admin
jesse at wingnet.net


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