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Tweaking the DVI/HDMI monitor for smoother video playback., Rant about jerky video playback.
psycho
post Apr 12 2012, 19:27
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Hello felow IT enthusiasts...

Something's been bothering me for quite some time now and I want to share it and I also hope someone might have some suggestions I haven't heard of before that could help me...

OK, as you might know, the video on a PC plays smoother if the refresh rate is set to a multiple of the video framerate. Say you have a video at 24 fps, it will playback smoothest at 72 Hz, 120 Hz. If you have a video at 25 fps it will playback smoothest at 75 Hz, 100 Hz. And if you have a video at 30 fps it will playback best at 60 Hz, 120 Hz.

I know all that and I live in a PAL area so most of my videos are at 25 fps and 24 fps. That means it is best for me if I set my Display Properties to either 75 or 72 Hz. MPC-HC player can switch these modes for me - you can define which fps go with which Hz. That's cool and I use that option.


Now we come to my problem. All of the above works if I connect my monitor via D-sub (VGA). It doesn't work with DVI and I haven't tried HDMI yet, as my manual says it's only for connecting to standalone players and not for computers (it explicitly says "HDMI not for connecting to a computer")... And I don't have the expensive HDMI cable anyway. So with DVI, my refreshrate is always 60 Hz on my monitor, no matter what I set on the PC. So the jerky video playback is always present as I almost never have 30 FPS video and for 25 and 24 FPS 60 Hz just isn't OK.

I can't help but wonder why on earth does DVI use the archaic mode of refreshing the screen?? As far as I know, LCDs don't refresh the screen as the CRTs do and DVI is meant for LCDs. So the logic suggests that there should be a mode of operation for LCDs to operate at "whatever-the-input-Hz" so to speak. I mean, it would rock to have such a mode of operation for DVI that it would actually send only changes of current display at any rate it happens... say with 24 FPS video, the DVI would refresh 24 times per second and that's it... Is there something like that? Can one achieve something similar with a PC and LCD monitor? Maybe HDMI (I have no experience with HDMI whatsoever so far)?


Well, that's it... I wish you all a smooth video playback and I hope someone can help me with some tricks. smile.gif


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andy o
post Apr 14 2012, 15:54
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One way to see which is right is to just check it visually. I can tell in many scenes (pans, titles) when my display is doing 72Hz on 24p content or if it's refreshing at 60Hz on 24p with 3-2 pulldown. Same with 25p (my display can also refresh at 100Hz). One other way I can tell, since it's a plasma, is looking through my camera's LCD. Since the camera's CCD also has a refresh rate, it will mismatch and I'd see an artifact similar to what you get when you videotape a CRT monitor. The screen glows brighter and darker, and depending on the frequency of this I can tell when the screen's rate has been changed. It of course won't tell you which refresh rate, but it will tell you immediately that it's changed. I don't know if this can be done with LCDs though.

I don't think those are DVI limitations. I think it's just many TVs only accept computer input through the DVI port and that's what's limited to 60Hz, as it's apparently your case. HDMI is practically single link DVI with different connectors. With simple DVI-HDMI dongles, one can even transmit 7.1 LPCM audio through DVI.

Regarding the EDID, I just know it can be done, but I've been lucky that I've never had to do it. A good place to start is here.
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