[MPlayer-users] Q on monitor refresh rate versus fps

[Oliver Seitz]

Am 30.12.2008, 21:48 Uhr, schrieb Matyas Sustik <mplayer.list at sustik.com>:

> Rashkae wrote:
>>> 2.  Should one sync the refresh rate to the video fps?  (Multiple?)
>>
>> The video driver should do this for you, if it's supported.
>
> So if I play two videos in separate windows requiring different refresh  
> rates
> (have not tried this yet) I wonder how could this work?  I just have no  
> idea
> how I would implement that properly...

I think the frames are decoded at the fps rate of the video. Each frame  
has a duration of, say, 1/24s or 1/25s or 1/30s. Even 15fps look quite  
fluent. Some early cartoos used 4fps, it looks jerky, but still like  
motion, not like slideshow.

Each decoded frame then is waiting for a vertical sync to be put on the  
screen before the next screen refresh. This delay will usually be less  
than 1/75s, or at most 1/50s. This is a very short time compared with  
usual video framerates. Thus waiting for the next retrace will not disturb  
the video display.

The time per frame when playing 24fps on 50Hz will be like 3/50, 2/50,  
2/50, ... [x12], 3/50, ... The difference between "long" and "short"  
frames is 1/50s or 0.02s. This difference becomes smaller at higher screen  
refresh rates.
While the time per frame in a telecined video will be like 1/30, 1/30,  
1/30, 2/30, 1/30, ... The difference between "long" and "short" frames is  
1/30s or 0.033s. Long frames are displayed for 0.066s, which can be  
noticed as jerk.

And: If you play two videos on one screen, usually both videos won't be  
fullscreen height. (You would need a really fancy screen for that...)  
There is a chance that the distortion would appear above or below your  
video windows.

So I think it is pretty possible to sync video display to screen refresh  
as long as the screen refresh is not too slow, which it isn't with today's  
displays.

Greets,
Kiste