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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 13 2012, 02:16
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You forgot to list all your hardware and software, including GPU and monitor. Most modern displays can do a variety of refresh rates over HDMI, but depending on the GPU you might have trouble with black levels, which is a whole other can of worms unless you're lucky.
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onkl
post Apr 13 2012, 02:19
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Try Media Player Classic Home Cinema with EVP Sync output. You might also want to update your graphics card drivers, or try another card if you have one at hand.

I never had any problems with regular PC displays, the only display that tends to judder with wrong refresh rates is the HDTV in the living room (connected to a HTPC). If your manual says anything about standalone players, you might have a "normal" telly too?
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psycho
post Apr 13 2012, 16:58
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OK, my hardware/software:
GPU: Radeon 4770
MONITOR: LG IPS236

OS: Windows XP PRO 32-bit


About EVR in MPC-HC. It's as cool as any other output if set up correctly. And my videos don't playback jerky because my PC would not be able to handle them, DXVA works just fine for HD video and SD video doesn't even wake up my CPU (AMD Athlon 64 X2 4000+ Brisbane).


To clarify: I can get perfectly smooth playback with D-sub @ 75 Hz for 25 fps videos and @ 72 Hz for 24 fps videos and @ 60 Hz for 30 fps videos. I just can't get the same with DVI and I don't know if I should go and buy HDMI cable just to later find out that it won't help me with my monitor.
To clarify further, most of my friend and my girfriend can only see the difference between jerky and non-jerky playback if I poit it out when it's happening (fast movement with sports channels, etc.)... So it isn't so much of a problem as it is an annoyance for me, because I'm just to sensitive and I just love smooth playback...

I don't own a TV, because I use IPTV via my computer, which is my media center for my living room... so no TV needed...


Thank you for your replies. smile.gif


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onkl
post Apr 13 2012, 18:09
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Here's a German review of your LCD: http://www.prad.de/new/monitore/test/2011/...nalverarbeitung
According to them, the manual states support for 56Hz to 75Hz, but they could only select 59/60Hz in the driver. Yet the judder test (with a moving bar) didn't reveal any problems. So I have to assume the display works fine and something else is causing your issue.

One thing to check could be Interlacing. It seems your display can deinterlace on its own, so make sure the outpute doesn't "look" interlaced to it, something that might not show up over an analog connection.

And concerning EVR Sync (not the normal EVR): Is that even available on XP? I remeber one problem with XP always was the lack of VSync on the desktop, unlike Vista and 7, which have VSync enabled.
You can hit CTRL+J to get some playback statistics in MPC and might want to play around with the render settings inside the context menu.

I doubt HDMI will make a difference. Essentially the same as DVI. But the price starts at 1€ online, so you might as well get one.
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psycho
post Apr 13 2012, 18:47
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Thanks for that review link (dankeschön! smile.gif). I'll read it whole later on.

I can also set only 59 Hz, 60 Hz and even 70 Hz when connected with DVI, but with D-sub I can select from 56 Hz to 75 Hz as it should be according to specs... so the specs clearly describe D-sub values. However, as I said, with DVI it doesn't matter what I select on the PC, the monitor is always at 60 Hz if I check it's menu... And that is what causes my problems.

Well, I will leave it connected via D-sub for now...


I will also try to somehow achive that some IPTV player will send interlaced picture to the monitor with the information that the picture need deinterlacing... I'm not sure how I will do this yet, but you gave me something to play with. smile.gif

EVR Sync on XP IS possible, but you must install NET Framework 3.5 Service Pack 1 (Full Package).

And I have also played with CTRL+J in MPC-HC and there I can see confirmation of the judder. No matter if I set overlay, VMR9, EVR Sync, the refresh rate matters and if it's a multiple of fps it's smooth and if not it isn't. How do I see that with CTRL+J? Well, when the refresh rate is a multiple of fps, the graph you see with CTRL+J is almost a perfect flat line, if however I look at the graph with say 60 Hz and a 25 fps video, the graph is a lot of triangles - jitter(?).


Thankyou for any input guys. smile.gif


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onkl
post Apr 13 2012, 19:44
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If the lines aren't straight, that doesn't necessarily mean the video stutters. The important thing is, that both lines stay parallel at each other. If they start to drive apart, snchronization will kick in and that's what's causing the judder. EVR Sync tries to spread this delay to every single frame, thus making the lines spiky but keeping them together. You basically trade one noticable judder for a lot of tiny ones. You may call it jitter, but I doubt that's what you're seeing.
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andy o
post Apr 14 2012, 02:10
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If the monitor is refreshing at 60Hz, you don't need any graphs, it's doing pulldown. psycho the monitor's EDID is probably only exposing those refresh rates to the monitor, since I don't think regular VGA does this, the GPU just sends whatever you tell it to. With digital connections, it sends what the monitor tells it it can take. You might wanna look into tweaking the EDID, but first check that the monitor supports those Hz at those resolutions (I'm assuming 1080p). Does the GPU allow for higher than 60 Hz in lower resolutions?
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psycho
post Apr 14 2012, 12:53
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Well... that makes sense, andy o. Any suggestions for software to tweak the EDID? smile.gif

Yeah, when connected to DVI, the lowest resolution is 800x600 and the highest refresh rate is 75 Hz. But even if I set this mode, the monitor will say it's runnig at 800x600@60Hz so... As said, it's OK on VGA.


I remember I have read somewhere that DVI can't work at any refresh rate other than 60 Hz, so everything we see as an option to select refresh rates with monitor connected via DVI is probably for compatibility only... To fool some software that other refresh rates are available... That's how I interpret this... Or has anyone ever successfully set refresh rate other than 60 Hz with DVI? And I mean really set it... not like me, when my PC says it's doing 75 Hz, but monitor says it's only 60 Hz...


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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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psycho
post Apr 14 2012, 23:33
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Yeah, what you describe, andy o, is exactly what I can see. When 24 fps video is played back @ 72 Hz via VGA it's smooth, when the same video is played back @ 60 Hz it's not smooth.

I will do a graphical interpretation of what I see. Say we have something scrolling horizontally on screen and imagine it would leave trails, this is what I can see:




And thanks for the avsforum link, I will check it out.


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psycho
post Jun 25 2012, 18:14
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All this time later and I have come up with the solution to my problem and I would like to share it so anyone with similar problem can maybe benefit from this...

So, the culprit was in AMD(ATI) "Catalyst Control Center". First, I had to uncheck "Enable GPU scaling" under "Digital Panel (DVI)", then I had to check under "HDTV Support", "Add 720p50 format to the Display Manager (PAL)" and I also checked "Add 1080p50 format to the Display Manager (PAL)" for full HD resolution to be able to refresh at 50 Hz. After all that I could use the "Force" button under "Displays Manager", "Displays Properties" to set it to either "HDTV Mode" 1280 x 720 @ 50 Hz or 1920 x 1080 @ 50 Hz.

Now I get super smooth 25 fps video playback!

So the "Enable GPU scaling" was forcing my monitor to always operate at 1920×1080@60Hz no matter what I have set. Strange, I can understand the resolution part of this logic but not the refresh rate part of it... Well, nevermind - solved! And just in time to watch UEFA 2012 championship via IPTV on the PC! smile.gif

(to be fair though, on this monitor I just can't see the difference in picture quality between D-sub and DVI... on my old monitor D-sub had some nasty noise, especially if displaying grey color... well, that's not the case with this one and all this quest for setting appropriate refresh rate via DVI was almost not necessary... almost, because 50 Hz was never before available to me and is even smoother than 75 Hz - guess it's because 50 is an even multiple of 25 and 75 is an odd multiple of 25...)


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