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Forcing other framerates

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Rolf Ernst wrote:
> On 4/26/2010 10:59 AM, meino.cramer at gmx.de wrote:
>> "Ing. Daniel Rozsny?"<daniel at rozsnyo.com>  [10-04-26 17:21]:
>>   
>>> meino.cramer at gmx.de wrote:
>>>     
>>>> RC<cooleyr at gmail.com>  [10-04-25 20:00]:
>>>>       
>>>>> On Sat, 24 Apr 2010 16:32:40 +0200
>>>>> meino.cramer at gmx.de wrote:
>>>>>
>>>>>         
>>>>>> I bought a new LCD monitor with 60Hz framerate.
>>>>>> When playing videos sometimes I git a distortet
>>>>>> screen (not only with mplayer!!!). I think, it
>>>>>> is because the video plays at 50Hz framerate
>>>>>> which then interferes with the 60Hz refresh rate
>>>>>> of the monitor.
>>>>>>            
>>>>> LCDs effectively do not have a refresh rate (or a "framerate").
>>>>>          
>>> LCD has a refresh rate! It refreshes the picture from top to bottom,
>>> just the "memory effect" of the screen is much bigger than on CRT. The
>>> LCD is effectively a visible dynamic memory (DRAM).
>>>      
>>    That means...?
>>    Displaying Image contents with a rate of 25Hz to a technology
>>    drawing every 1/60 second a picture...gives...?
>>
>>   
>>>     
>>>>> You've not described what this "distortet screen" problem is, so
>>>>> nobody
>>>>> can possibly help.
>>>>>
>>>>>
>>>>> -- 
>>>>> Ha. I'm the idiot.
>>>>> _______________________________________________
>>>>> MPlayer-users mailing list
>>>>> MPlayer-users at mplayerhq.hu
>>>>> https://lists.mplayerhq.hu/mailman/listinfo/mplayer-users
>>>>>
>>>>>          
>>>> If LCDs have no framerate or refresh rate, they will not draw
>>>> frames from top to bottom? How then?
>>>> A try for a better explanation:
>>>> Certain videos (for example the Neo<->Smith fight sceen in Matrix
>>>> Revoluitions) with fast changing lightning conditions expose some
>>>> screen distortions.
>>>> They are of two kind:
>>>> The upper half of the screen is still in "bright condition"
>>>> when the lower half is in "dark condition" -- what comes first and
>>>> where this "break" is, depends. Also varying is the position
>>>> of this "break" on the screen.
>>>>        
>>> That is a missing vertical synchronization - what -vo are you using? On
>>> what video card and which drivers? Usually on dualhead the vsync is
>>> hard to get..
>>>      
>>    Oh, oh...some mails ago I got a hint to disable all VSYNCs in the
>>    nvidia settings...
>>
>>    So...using -vo xv gives me the fastest (read: normal speed) video
>>    with audio and video in sync.
>>    Other drivers result in the message that my two core 3800+ AMD
>>    CPU is to slow....(?)
>>    My gra?hics card is ai
>>    nVidia Corporation G73 [GeForce 7600 GT] (rev a2) which run with
>>    the current nvidia drivers on a Linux box.
>>    I myself and my computer each uses only one head ;)
>>    Most of the time I use my own... ;) ;)
>>    I disabled AutoTwinDevice in the Xorg.conf as I did with
>>    TwindDevice (dont remember the correct names of that parameters, but
>>    was something like that.).
>>
>>    Since 60Hz is common for LCD I am asking myself, whether I am the
>>    only one having problems with playing 25Hz/region 2 contents...?!
>>
>>    Since it also happens for example with the fight scene Neo<->Agent
>>    Smith in Matrix Revolutions (DVD, region 2) I think, it is not
>>    a bug in the video itsself....
>>
>>    I am a little (read: very) frustrated, since this monitor is new
>>    and I like its colors and features, but...
>>
>>    So any help to circumvent this problem is *very* appreciated! :O)
>>
>>    Have a flicker-free evening! :O))
>>    Best regards,
>>    mcc
>>
>> -------
>>    
> Somewhere along this thread someone stated that the LCD is refreshed 
> bottom to top. This is simply not true (suggest 
> http://en.wikipedia.org/wiki/Refresh_rate). The actual 'flicker' is 
> around 200Hz which I doubt comes into play in this case.
> 
> Let me reiterate that I do what you are doing often and do not observe 
> this symptom. Maybe it is some sort of interaction between graphics card 
> and monitor?

The problem is just VSYNC (which requires at least double buffering).
It is often visible from a fullscreen flash video..

Back to the LCD question. The screen is refreshed at 60 or 72 or 75 Hz 
(newer models with 3D support at 120Hz). From top to bottom, believe me 
or not. But the afterglow is significantly longer than of CRT (which has 
about 1/3 to 2/3 of vertical time at 60 Hz), LCD has about 0.1 to 1 
second, which is MORE than one frame (at 60Hz so you do not see it 
flickering).

If you are looking at 2 frames at one time, it means, that the computer 
switches the frame in middle of screen refresh = VSYNC problem.

If VSYNC is missing, the screen refresh and movie framerate can be any 
number, different or same, does not matter. Without proper vsync and 
double/triple buffering you will get always a cut frame.

As the OP mentioned, it is very visible at dark+bright scene change 
(e.g. a lightning, of photo flash, or anything similar) where you 
clearly see two frames - half of old, half of new. Fix VSYNC.

PS. The wikipedia is not correct about CCFL, it runs at tens of kHz 
frequencies, not 200. I work with both CCFL and LCD, so I can tell.. 
don't believe everything you read.

PS2: There are some LCD's which really flicker - to gain low delay, they 
shut off CCFL while the image is changing - so you do not see the 
transition, but a crisp image. But it is bad, since it flickers :)

Daniel


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