New ToastyX CRU Vertical Total Calculator for Quick Frame Transport (QFT)

[ToastyX]

Custom Resolution Utility (CRU) 1.5.2 has a new vertical total calculator that makes it easier to create lower refresh rates with a specific pixel clock, which can be used to implement Quick Frame Transport (QFT).

1. Start with an existing high refresh rate detailed resolution:



2. Change the timing to "Vertical total calculator":



3. Enter a lower refresh rate.

The vertical total is automatically calculated based on the new refresh rate.

In this mode, the frequency radio buttons determine the rounding method:

• If refresh rate is selected, the pixel clock is rounded down to get closer to the entered refresh rate.
• If pixel clock is selected, the pixel clock is left unchanged, but the actual refresh rate might be slightly higher than entered.

[elexor]

Thanks for this update, This is much easier then how I was doing it before.

[Chief Blur Buster]

Fantastic update, ToastyX! Some minor updates:
1. You should add (QFT) to the menu so it’s more self explanatory. For example menu should say “Vertical total calculator (QFT)”.
2. Also, you should add a “Back Porch Calculator (QFT)” option too, to modify only the Back Porch, as some panels prefer that.

You may want to rename the terminology a bit, because it’s really “Front Porch Calculator (QFT)” and “Back Porch Calculator (QFT)”. Or perhaps “Vertical Total Calculator Via Front Porch (QFT)” and “Vertical Total Calculator Via Back Porch (QFT)”.

I realize old EDID has a size limit for Back Porch, but that isn’t a problem for CEA861 extension blocks (AFAIK). You may simply want to clamp the range like you do for other numbers whenever it’s edited in the legacy EDID slots. At the end of the day, newer panels that are FreeSync compatible are almost always “back porch intolerant” (whether VRR or non-VRR) but occasionally sensitive to large front porches. So you should provide both options, ideally.

Additional Tips for End Users

1. I noticed some monitors have multiple different EDIDs for only slightly different refresh rates (or VRR ON/OFF), and sometimes one of the two EDIDs behave better for QFT. So if you go OUT OF RANGE or a blank screen (or artifacts), try deriving a different refresh rate or turning on/off FreeSync.

QFT /usually/ works better with FreeSync=ON, because QFT is simply a fixed-Hz “FreeSync” signal. However, FreeSync=OFF works better for strobing, so you need to experiment a little sometimes.

2. Sometimes you can QFT a high-Hz mode (240Hz) only down to a lower Hz, such as 65 Hz. This is because some monitors prefer ultralarge Back Porch instead of ultralarge Front Porch. A workaround is to simply hunt for the lowest refresh rate above your target refresh rate. Then after you’re done, switch back to “Manual” and modify the refresh rate downwards manually (without changing Vertical Total further), e.g. 65Hz->60Hz. (If you made a working 65Hz QFT but not a 60Hz QFT)

3. Since CRU’s Vertical Total Calculator only modifies Front Porch (AFAIK?), this can cause compatibility issues with panels that are more Back Porch insensitive than Front Porch insensitive. You may have to skip CRU’s Vertical Total Calculator and modify the Back Porch instead.

[ToastyX]

You have it mixed up. The vertical total calculator already modifies the back porch. The front porch is what's severely limited. EDID limits the vertical front porch to 63, and CTA-861 extension blocks use the same format. DisplayID is what has higher limits. The front porch version would only be possible with DisplayID, so I'm going to hold off on that until CRU 2.0, which will be able to automatically use EDID or DisplayID depending on the parameters. It will also fill in the highest refresh rate at the native resolution when adding a new resolution, so that will save a step. Every resolution will also be in one list, so no more hunting through extension blocks either.

The problem with the QFT acronym is that's not the only name I've seen. There's also Fast VActive (FVA), and the VT tweak. I was originally going to call it "Fixed pixel clock" but adding the rounding mode made the pixel clock not so fixed. The vertical total is what it's actually calculating (vertical total = pixel clock ÷ refresh rate ÷ horizontal total). The back porch just changes as a consequence of that. I was thinking of putting two radio buttons on the vertical side to choose between calculating the front porch and back porch, but maybe two separate entries like you suggested would be easier to understand.

[Chief Blur Buster]

You have it mixed up. The vertical total calculator already modifies the back porch. The front porch is what's severely limited.

Oh, good catch! I remembered one of the two was severely limited.

Yes, hold off till CRU 2.0.

The problem with the QFT acronym is that's not the only name I've seen.

QFT is a generic term and is getting more and more common -- since Blur Busters already use that terminology to popularize QFT. So you probably should just say the most popular terminology:

Quick Frame Transport (Fixed VT)

Or as a compromise, with a minor edit:

Fixed Vertical Total (QFT)

This is because:

There are 168,000 search results when you google "Quick Frame Transport" in quotes.
There are only 438 search results when you google "Fast Vactive" in quotes.
There are few search results when you google "Fixed Vertical Total" (or its plural / acronyms) in quotes.
There are few search results when you google "Large Vertical Total" (or its plural / acronyms) in quotes.

This in large part thanks to Blur Busters popularizing the QFT terminology, too.

Honestly the Fast VActive is a very rarely used terminology in the tweaker forums, mainly used in researcher papers and elsewhere (AFAIK), so I would recommend including the QFT acronym to make it more intuitive to people who follows the gradually expanding Blur Busters HOWTOs. QFT is more intuitive to everyday gamers because it sounds like it reduces input lag.
- Fast Vactive is something mainly found in tech documents (e.g. APIs, specs, engineering)
- People who know what QFT means, usually don't know what Fast Vactive is.
- People who know what Fast Vactive, usually already know it as QFT.
- So QFT is the superset-familiarity terminology.

There will be a massive boom of QFT research so as a trailblazer, when people create latency tests (photodiode) for QFT, they will read out what your app does (Quick Frame Transport). So I highly recommend using the prevailing popular term that is increasingly being advertised to end users.

[Chief Blur Buster]

TL;DR: What is Quick Frame Transport For?

For new readers...
- QFT reduces input lag on many displays
- QFT reduces strobe crosstalk (for strobing)
Note: QFT is a non-VRR technology, ideal for reducing latency of fixed-Hz modes.

Links To Related Threads

1. Understanding Quick Frame Transport (QFT)
2. Old Quick Frame Transport HOWTO

Crosspost of QFT Explainer

People who may have heard of a new method of delivering refresh cycles faster. We're very familiar with this, but few people are.

See HDMI Version 2.1 on HDMIFORUM.org which says:

HDMI Quick Frame Transport (QFT) reduces latency for smoother no-lag gaming, and real-time interactive virtual reality.

But what the hell is Quick Frame Transport? Well, it's simply a large blanking interval.

First, if you have seen those numbers in a Custom Resolution Utility, they are just simply mapped spatially in signal layout:



Vertical Total = the entire height of this.
And VBI = Vertical Blanking Interval = (The sum of Vertical Front Porch + Vertical Sync + Vertical Back Porch).

Around here, we sometimes call this the Large Vertical Total trick, which also has other benefits such as reducing strobe crosstalk.

Normally, refresh cycles are transmitted one after the other, in tight fashion with a tiny blanking interval:

However, it's possible to scanout quicker, such as delivering 100Hz refresh cycles in 1/144sec:

It's possible to go even further, such as delivering 60Hz refresh cycles in 1/240sec! Basically, a frame-delivery acceleration of 4x factor, for supported platforms.

HDMI Quick Frame Transport, while specified by HDMI, the fundamental technique also works on DisplayPort and DVI connections, since it's simply a large blanking interval. A refresh cycle is transmitted faster, with a longer pause between refresh cycles.

Also, some 240Hz monitors can only scan-out their panels at full velocity (1/240sec). So they have to buffer an incoming slow-scanning 60Hz refresh cycle over the cable, before scanning-out in 1/240sec. By using Quick Frame Transport, you can do realtime concurrent LCD panel scanout in sync with cable scanout, reducing the input lag of 60Hz or 120Hz signals (e.g. XBox One consoles) on a 240Hz displays.

Ideally, a display has to advertise this feature correctly via the correct EDID/DisplayID info, to inform a computer that it supports a Quick Frame Transport mechanism. However, many existing 144Hz and 240Hz monitors support Custom Resolution Tweaking to create large VBIs, so it would be very easy to add Quick Frame Transport capabilities to these displays, for supported signal sources. Monitor manufacturers should add information to their HDMI EDIDs to include the Quick Frame Transport feature. FreeSync compatible LCDs are relatively easy to make QFT compatible.

(Currently, most 240Hz monitors are very bad at 60Hz consoles, since they only do bufferless scanout at 240Hz -- because they buffer a 60Hz scanout signal and does a full-velocity scanout on 240Hz LCD panels. Unless they're made to support a Quick Frame Transport at 60Hz with a large Vertical Total of >4000 scanlines for a 1080p signal).

Now you understand better!

______

EDIT: Want to do QFT on your computer? There's a new HOWTO for creating Quick Frame Transport:
HOWTO: Quick Frame Transport (QFT) - Large Vertical Totals (reduce lag, reduce crosstalk)

[Chief Blur Buster]

By the way, QFT tip for DLP projector users to reduce DLP lag!

Almost all cheapie 4K 60Hz pixel-shifter DLP projectors (sub $1000) apparently supports undocumented 1080p QFT 120Hz, when you disable pixel shifting (Silent Mode) and downrez to a 1080p signal which is native to the DLP chip (It only does 4K via physically shifting the DLP chip spatially around for those in-between pixels). And DLP input lag decreases dramatically!

QFT 120Hz works perfect on my Viewsonic PX747-4K (Silent=ON). Since most of DLP input lag is global processing lag (inside the projector), 120Hz decreases this lag by 8ms and QFTing it decreases the lag again by another 4ms.

1. Derive from the 4K 60Hz pixel clock to create a 1080p 120Hz QFT scignal.
2. Load your max pixel clock EDID mode. Write down the number.
3. Now select your 1080p 60Hz EDID mode.
4. Select "Manual" timings formula.
5. Lock radio button on Pixel Clock and type in the same number.
6. Select "Vertical Total Calculator" formula and edit refresh rate to 120, the highest non-frameskipping refresh rate available.
7. This creates a 1080p 120Hz QFT (~VT2250)

Several permutations of these steps also works; this may be simplified -- key is a 120Hz QFT signal same pixel clock as 4K 60)
In the past, I used Manual and modify the 1080p 60Hz mode -- double the refresh rate (60->120) and then double the vertical total (1125->2250) and you end up having the same Pixel Clock as a 4K 60Hz signal.

Lag reduction is caused by:
- It is a 120Hz signal that transmits refresh cycles in 1/240sec from GPU to the DLP's internal framebuffer.
- It transmits a whole refresh cycle globally into the DLP's processing framebuffer ~12.9ms sooner than any regular 60Hz EDID signal! The latency savings is (1/60sec - 1/240sec) for the entire transmission of the refresh cycle from the first visible pixel through the last visible pixel.

Note: 1080p 240Hz non-QFT sorta works too (visible) but it frameskips, so I backed it down to 120Hz and added QFT. The frame transmission is the same velocity either way (1/240sec between GPU memory to DLP projector memory)

[Mr1991]

Going to sound like a noob here, but if QFT is for lowering input lag, but you have to lower your refresh rate to use it, doesn’t that make it obsolete?

[Discorz]

Going to sound like a noob here, but if QFT is for lowering input lag, but you have to lower your refresh rate to use it, doesn’t that make it obsolete?

QFT is for monitors that don't utilize it at lower refresh rates. And most monitors don't.

[Chief Blur Buster]

QFT is for monitors that don't utilize it at lower refresh rates. And most monitors don't.

See below. QFT is useful for more than just reducing input lag. It is also useful for reducing strobe crosstalk.

Going to sound like a noob here, but if QFT is for lowering input lag, but you have to lower your refresh rate to use it, doesn’t that make it obsolete?

No, because:

QFT is not just for lowering input lag; it can reduce strobe crosstalk too.

Strobe crosstalk is double images during strobing that still persists at framerate=Hz, because LCD GtG is not fast enough to be made invisible between refresh cycles (See famous old LightBoost video at www.blurbusters.com/lightboost/video as well as the Pixel Response FAQ at www.blurbusters.com/gtg-vs-mprt ....)



Utilizing QFT can solve a lot of this by hiding more LCD pixel response unseen from human eyes. A faster LCD scanout (that QFT can help) means more time for LCD GtG to finish in total darkness between strobe backlight flashes.

Strobing looks higher quality at framerate=Hz, so sometimes you have to lower Hz to match GPU's framerate. This can make it more fun to play certain games like Cyberpunk 2077 or other GPU-demanding if you're a motion blur reduction purist. Those games can't do 240fps.

Refresh rate headroom makes strobing higher quality. Many strobe purists prefer a superior 120Hz strobe mode over an inferior 240Hz strobe mode.

Retro content, such as emulators, where you are stuck with low Hz. QFT can reduce the input lag of emulators.

Also, remember virtual reality. The Quest 2 LCD has to run at ultrafast scanouts too -- it's technically theoretically capable of higher refresh rates, but instead Oculus (Meta) uses the headroom to eliminate strobe crosstalk.

Etc. There's more reasons, but this should micdrop the "obsolete" debate. At least until we've got blurfree sample-and-hold (Where 1000fps+ 1000Hz+ could make strobing obsolete someday)

______

In other words:

QFT is not just for lowering input lag. It also reduces strobe crosstalk, by hiding more LCD GtG in the VBI between refresh cycles, unseen by human eyes. 60Hz refresh cycles can be made to scan-out in 1/240sec on some 240Hz monitors, leaving 3/240sec between refresh cycles (12.9ms blanking interval!) -- a blanking interval giant enough for a truck to drive through. This was utilized on the XG2431, as seen at www.blurbusters.com/xg2431 with Strobe Utility.



On the XG2431, you can get to zero strobe crosstalk with a QFT 60 Hz mode. Here's an image:



With QFT, the Vertical Total at 60 Hz is between around 4000-4600, depending on what mode you derive from.

On some 240Hz panels, doing a QFT 120fps 120Hz (combined with VSYNC ON, or a low lag clone thereof such as RTSS Scanline Sync) can sometimes produce a superior playing experience over 240Hz for some people, because of its perfectly blurfree nature similar to framerate=Hz on a CRT tube. As long as it's fully stutter/jitter free.