[MPlayer-users] Re: Framerate vs. monitor refresh rate

[Morris Beverly]

>> I've tried to explain the kind of tearing is along many
>> trapezoidal slices all at the same time.  This suggests that
>> DVI-D has several scanlines being updated all at the same
>> instant in parallel, which doesn't fit the quoted material you
>> provided, presuming "line by line" means SEQUENTIALLY as seen
>> by the human.
>>
>> Also the same kind of tearing is seen with a normal CRT
>> monitor on a VGA connection, not DVI-D.  Now surely there is
>> only one e-beam inside the CRT, which would produce a kind of
>> half-way-done frame -- not the 10 or 20 or 30 separately torn
>> trapezoidal slices being seen even when using the CRT.
>>
>> The tearing being seen just does not fit this "normal" way of
>> thinking about refresh rates, no matter what kind of monitor /
>> interface being used.
>
>
> Yes, when you single step, the tear will clean itself up, it only 
> occurs when the image is changing. If the image
> is static, the tear is still there - but you cannot see it because the 
> images are the same. The same goes for video the
> tear effect is most visible when the image changes a lot frame to frame.
>
> Everything you describe is entirely consistant with a lack of 
> syncronisation to the VBlank period, except that it occurs
> at multiple vertical positions at the same time... So I dont know 
> whats causing it... but my problem is definitely a vblank
> one, and I really just wanted to point out that DVI-D still uses a 
> normal CRT-like scan pattern for the display updates.


It is possible that you are in fact only getting one tear per frame.  Because of persistence of vision, sync problems often seem to be happening simultaneously when they are actually on individual frames and your eye is making the glaring errors pile up into one percieved image.  I used to see this sort of thing a lot with bad sync on crt projectors.

It will be very hard to diagnose this without some sort of recording equipment.  I'd just borrow a regular camcorder and shoot the screen.  You may get lucky & get enough data to be useful over the course of a minute or so of recording.

I would really try to get some specific help on the VBlank thing from mac people.  I've got to say I think this is your problem too.

good luck,

morris