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Does GSYNC work with video players? [edit: yes, sometimes]

Talk about NVIDIA G-SYNC, a variable refresh rate (VRR) technology. G-SYNC eliminates stutters, tearing, and reduces input lag. List of G-SYNC Monitors.

Re: Does GSYNC work with video players?

Postby Chief Blur Buster » 26 Jan 2014, 14:04

Nimbulan, can you describe the grainy behaviour of the repeat refresh? I have two theories, including LCD inversion behaviour and variable freshnesses of pixels. The color change of 30fps is extremely subtle versus 144fps, far less than native non gsync 120hz versus 144hz. NVIDIA did a very good job at suppressing color variances of variable refresh rate, in my opinion.
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Re: Does GSYNC work with video players?

Postby nimbulan » 26 Jan 2014, 14:11

Chief Blur Buster wrote:Nimbulan, can you describe the grainy behaviour of the repeat refresh? I have two theories, including LCD inversion behaviour and variable freshnesses of pixels. The color change of 30fps is extremely subtle versus 144fps, far less than native non gsync 120hz versus 144hz. NVIDIA did a very good job at suppressing color variances of variable refresh rate, in my opinion.

I generally keep my display at 120 Hz and I can't tell any color difference when G-sync is operating at 30 Hz. The graininess I see is difficult to describe, it seems like I can see something jittering back and forth sideways within each pixel. It's almost like I can see the crystals twisting back and forth. I first noticed it in the MSI Afterburner overlay since the graininess is very visible on that pink color it uses, even from a normal viewing distance. Other colors I have to look much closer to notice it.
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Re: Does GSYNC work with video players?

Postby Chief Blur Buster » 26 Jan 2014, 22:37

nimbulan wrote:
Chief Blur Buster wrote:The graininess I see is difficult to describe, it seems like I can see something jittering back and forth sideways within each pixel. It's almost like I can see the crystals twisting back and forth. I first noticed it in the MSI Afterburner overlay since the graininess is very visible on that pink color it uses, even from a normal viewing distance. Other colors I have to look much closer to notice it.

I bet that is the checkerboard pixel pattern found in common LCD voltage balancing algorithms (inversion / pixel-walk). See http://www.testufo.com/inversion and follow the lagom and techmind links.

With GSYNC,the inversion walk artifact goes at a variable speed that accelerates at a higher frame rate. Or even erratically, at 25-30fps due to the repeat refresh occurring long after previous frame but very shortly before the next frame.

Nearly all LCDs, even IPS, uses inversion to voltage-balance the panel, but it does seem to amplify a little bit during GSYNC 25-30fps when one inversion pattern spends more time than the opposite inversion pattern, due to the non regular interval of the refresh passes. Possibly, NVIDIA may want to lower the minimum Hz to 20 in order to cover these bases, including 24fps films, to reduce inversion artifacts during these potentially common use cases.
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Re: Does GSYNC work with video players?

Postby nimbulan » 26 Jan 2014, 23:46

Chief Blur Buster wrote:I bet that is the checkerboard pixel pattern found in common LCD voltage balancing algorithms (inversion / pixel-walk). See http://www.testufo.com/inversion and follow the lagom and techmind links.

Yes you are absolutely right. It looks like a standard inversion pattern of slightly lighter and slightly darker pixels. It is sometimes stationary, or will appear to jitter left and right quickly depending on the exact framerate. It is surprisingly not visible under normal viewing conditions for the vast majority of colors. I have so far only noticed it in the pink color of the MSI Afterburner overlay from a normal viewing distance but can see it in all colors if I look closely at the monitor.
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Re: Does GSYNC work with video players?

Postby Chief Blur Buster » 27 Jan 2014, 14:09

nimbulan wrote:
Chief Blur Buster wrote:I bet that is the checkerboard pixel pattern found in common LCD voltage balancing algorithms (inversion / pixel-walk). See http://www.testufo.com/inversion and follow the lagom and techmind links.

Yes you are absolutely right. It looks like a standard inversion pattern of slightly lighter and slightly darker pixels. It is sometimes stationary, or will appear to jitter left and right quickly depending on the exact framerate.
The stationary-inversion-pattern at 24 frames per second is likely because the refreshes are not spaced apart at exact intervals.

During 24fps on GSYNC, you've got refesh cycles displayed for 33ms then 9ms then 33ms then 9ms then 33ms then 9ms.
This is because of the 30Hz automatic repeat-refresh occuring after 33ms, but there's only 9ms until the next 24fps frame beginning to display. So, during 24fps, this can cause the stationary inversion pattern look, as the dot crawl is not temporally masking itself out.

If the video player can be made to repeat-redisplay of the same at a regular 48fps or 72fps (double or triple duplicate frame), the problem would solve itself because that would be within the GSYNC 30fps to 144fps range.
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Re: Does GSYNC work with video players?

Postby Valyrian » 27 Jan 2014, 16:22

So does that mean that when you use GSYNC with a video that has a frame rate below 30fps, you will see that graininess, like the one on the moving square in the testufo inversion link Chief posted, on the whole screen? Also, why does GSYNC have a minimum frame rate in the first place before it starts repeating frames? I thought that with a sample-and-hold refresh cycle the rate wouldn't really matter.

Chief Blur Buster wrote:Possibly, NVIDIA may want to lower the minimum Hz to 20 in order to cover these bases, including 24fps films, to reduce inversion artifacts during these potentially common use cases.

I for one was surprised this wasn't implemented from the start, precisely because most videos have frame rates lower than 30fps.
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Re: Does GSYNC work with video players?

Postby Chief Blur Buster » 27 Jan 2014, 16:52

Valyrian wrote:Also, why does GSYNC have a minimum frame rate in the first place before it starts repeating frames? I thought that with a sample-and-hold refresh cycle the rate wouldn't really matter.

The LCD state can slowly decay into white (or black). When you suddenly remove panel drive power from an LCD ribbon connector, the picture fades to white (or black) over a time period of a few seconds. It's like DRAM, which requires memory refresh cycles.

I think 20Hz is a very doable lower-end GSYNC refresh rate, and conveniently fixes the 24fps film use-case.
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Re: Does GSYNC work with video players? [edit: yes, sometime

Postby shadman » 27 Jan 2014, 16:55

Valyrian wrote:So does that mean that when you use GSYNC with a video that has a frame rate below 30fps, you will see that graininess, like the one on the moving square in the testufo inversion link Chief posted, on the whole screen? Also, why does GSYNC have a minimum frame rate in the first place before it starts repeating frames? I thought that with a sample-and-hold refresh cycle the rate wouldn't really matter.

Chief Blur Buster wrote:Possibly, NVIDIA may want to lower the minimum Hz to 20 in order to cover these bases, including 24fps films, to reduce inversion artifacts during these potentially common use cases.

I for one was surprised this wasn't implemented from the start, precisely because most videos have frame rates lower than 30fps.


I suppose its due to Nvidia marketing it firstmost for games, and repeating a few frames for those dips under 30fps seemed a better option than holding a picture still for more than 16ms. Most likely a more "lesser of two evils", although for other applications, such as video players, it would seem better to have a lower limit of 24hz, instead of 30Hz.

Just my thoughts, but I want to see if anyone else has a possible better explanation.
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Re: Does GSYNC work with video players?

Postby nimbulan » 27 Jan 2014, 19:41

Valyrian wrote:I for one was surprised this wasn't implemented from the start, precisely because most videos have frame rates lower than 30fps.

I'm pretty sure that 30 Hz was chosen to eliminate the possibility of picture degradation and flickering that may be caused by refreshing slower than that. The inversion artifacts are barely visible under normal viewing conditions and 24 fps video will still play smoothly as is. It is 29.97 fps video where the problem is most likely to occur, but the timing may still be close enough to not cause issues.
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Re: Does GSYNC work with video players? [edit: yes, sometime

Postby Chief Blur Buster » 27 Jan 2014, 20:14

In my next roughly-weekly digest email to NVIDIA (collecting all sensible feature requests), I will include a mention of this thread to possibly convince them to lower the GSYNC floor to about 20-23fps, to accomodate movie cases. Or at least down to ~29fps, to at least solve the 29.97fps video file problem. Lowering the GSYNC limit to ~20fps would would look great for 4K 24Hz movies, and 4K 48Hz HFR movies, in those apparently pre-existing movie players that run in Full Screen mode (and automatically takes advantage of GSYNC).

And having a slightly lower GSYNC limit would benefit games, too. For 4K gameplay pushing GPU limits, where it would often dip slightly below 30fps as low-latency slow dips to 25-30fps would be more-or-less playable rather than be suddenly stuttery. 30fps on non-GSYNC is the minimum frame rate most people are comfortable at, but GSYNC can easily lower the "playability" threshold a little bit, down to approximately ~24fps, the cinematic level, provided that the individual display refresh scanouts is done quickly (to keep input lag low). Personally, I wouldn't dare play at only 24fps, and I'd pay to upgrade my GPU instead, but I know a lot of people want to buy 4K, and a lot of their GPUs aren't going to guarantee >30fps at 4K, so obviously you definitely do want a lower GSYNC limit for 4K.

They probably didn't seriously focus on movies when designing GSYNC, but it is apparently very clear that movies are a worthy GSYNC use case, especially VFR video files that changes framerates while they are playing (24fps movies with embedded 60fps video commercials or 48fps HFR segments)! And theoretically, future gameplay recorders may record true frame-granular VFR video files, allowing perfect GSYNC playback of game video on GSYNC displays. I know people have been interested in buying GSYNC monitors solely to play video material more smoothly, and it theoretically is a fairly simple change to lower the GSYNC floor to 29Hz (to accomodate 29.97fps video) or down to <24Hz (to accomodate 23.976fps material or 24fps material). Even though 24fps @ 24Hz will be prone to the slow-moving inversion artifacts, it's better than 24Hz + stationary inversion artifact (of the current status quo, caused by the repeat refresh timings).
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       To support Blur Busters:
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