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Frame Rating Dissected: Full Details on Capture-based Graphics Performance Testing

Capture Hardware and Extracting the Data

Capture Hardware

Once we have the overlay working, the next step in our Frame Rating process is to actually capture the video for later analysis.  While that sounds easy, it is far from the case.  Capturing the video on the testing system is out of the question. Instead we are using an external capture system built around an Ivy Bridge platform and a high-end capture card from Datapath, the VisionDVI-DL.

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This card is capable of capturing video at 2560x1600 at 60 Hz with throughput as high as 650 MB/s.  We were actually the first customer for this card in the US and have spent quite a few days on the phone with driver engineers to make sure this kind of testing process was successful.  Meant mainly for single frame captures, getting the VisionDVI-DL to really meet the specifications turned out to be a more complicated process than we’d hoped.  The good news is we have it all figured out now and can reliably capture the necessary video.

The VisionDVI-DL essentially acts like and shows up as a monitor to the system.  It reports an EDID (extended display identification data) to the graphics card that is set through the driver on the capture system.  I am able to emulate a 1920x1080 monitor at 60 Hz refresh and up to a 2560x1440 @ 60 Hz as well.  Using a Gefen dual-link DVI splitter we can connect a single display output to the NVIDIA or AMD GPU (to avoid the issues of power consumption and GPU utilization with multiple monitors attached) and split the signal to our capture card and to a monitor for us to actually play the games.

With a data rate of nearly 500 MB/s when capturing video at 2560x1440 @ 60 Hz, some serious storage speed was needed for this capture system.  I decided to use our Pegasus R4 Thunderbolt array coupled with a set of four Corsair Force GS 240GB SSDs running in an RAID 0 array, giving us about 900 MB/s of write capability.

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I cannot overestimate the importance of a completely correct capture in this step of the Frame Rating process.  If you deviate from the 60 Hz record rate even a single frame the data becomes basically useless.  Dropping a frame on the capture side would show up as dropped frames from the graphics card so avoiding that is paramount.  The software used for this capture will likely be VirtualDub on other sites that you see, and that was the program we used originally too.  However, the inability to automate the settings and having to re-adjust the options each time you load the program became a hassle so we developed our own that uses DirectShow filters and the Windows Platform SDK. 

 

Extracting the Data

Once you have the recorded raw AVI file, (that is about 25GB – yes GB – from a 60 second capture at 2560x1440) the next step is to actually read the colored bars and generate frame time data, runt data and drop data.  Using a basic DSP application, the extractor reads in each frame of the video sequentially and determines the number of scanlines in height that each color on the overlay bar has and records that information in an XLS file.

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This is probably the most fool-proof part of the process.  I have uploaded a few example XLS files right here for you to see the output.

March 27, 2013 | 09:16 AM - Posted by grommet

Hey Ryan, is the variable "t_ready" that the text refers to "t_present" in the diagram two paragraphs above?

March 27, 2013 | 09:22 AM - Posted by Ryan Shrout

Yes, fixed, thanks.

March 27, 2013 | 10:20 AM - Posted by Prodeous (not verified)

I was just wondering.. since the capture and analysis system relies on the left bar only, why doesn't it trunckate the rendered frame it self and keep only 1-3 pixels from the left side of the frame?

For some tests if you want to show off the specific "runts" "stutters" then you can keep it the entire frame captured.

But for most tests, you can record only the left colour bar and do analysis on that bar only, therefore you will not have to save the 600GB per second of uncompressed frames.

Just a thought.

March 27, 2013 | 10:40 AM - Posted by Ryan Shrout

We have that option (notice the crop capture option in our software) but we often like to reference recorded video down the road.

March 28, 2013 | 08:53 AM - Posted by Luciano (not verified)

If you write a piece of software with that "colored" portion only in mind you dont need any of the additional hardware and any user could use it just like Fraps.

March 28, 2013 | 07:02 PM - Posted by Anonymous (not verified)

LOL - AMD you are soooo freaking BUSTED !

Runt frames and zero time ghost frames is an AMD specialty.

AMD is 33% slower than nVidia, so amd pumped in ghosts and runts !!

Their crossfire BF3 is a HUGE CHEAT.

ROFL - man there are going to be some really pissed off amd owners whose $1,000 dual gpu frame rate purchases have here been exposed as LIES.

Shame on you amd, runts and ghosts, and all those fanboys screaming bang for the buck ... little did they know it was all a big fat lie.

March 29, 2013 | 02:42 AM - Posted by Anonymous (not verified)

true words of a fan boy.

May 26, 2013 | 08:23 PM - Posted by Johan (not verified)

Even i have Nvidia, but his comment, was really a fan-boy comment.

March 27, 2013 | 09:43 AM - Posted by Anon (not verified)

Run the benchmarks like any sane gamer would do so!

Running v-sync disabled benches with 60+ fps is dumb!

Running v-sync enabled benches with 60- fps is way more dumb!

YOU'RE DOING IT WRONG!

March 27, 2013 | 10:00 AM - Posted by John Doe (not verified)

Don't forget that V-sync also sometimes fucks shit up.

The best solution is to limit the frames on the game end, or using a 3rd party frame limiter.

March 27, 2013 | 10:51 AM - Posted by Anon (not verified)

And sometimes disabling it fucks physics like in Skyrim.

Your point?

March 27, 2013 | 10:18 AM - Posted by grommet

Read the whole article before commenting- there is an entire page that focuses on your argument (surprise- you're not the first to suggest this!!)

March 27, 2013 | 10:32 AM - Posted by John Doe (not verified)

And if you have actually watched one of his streams, you'd have seen that he INDEED IS doing it "wrong".

When he was testing Tomb Raider, the card was artifacting and flickering and shimmering. It was complete and totally obvious that he didn't know what he's doing.

March 27, 2013 | 10:31 AM - Posted by Anonymous (not verified)

To the guy who says "you're doing it wrong".

Not true. He's doing it right. Many hardcore gamers run v-sync disabled over 60 fps, and only a few of the scenarios tested are consistently over 60fps.

And read the story to see the OBSERVED FPS is much less in many cases, not just the FRAPs FPS (which does not give proper info at the end of the pipeline (at the display) what users actually see).

March 27, 2013 | 10:38 AM - Posted by John Doe (not verified)

There's absolutely nothing "hardcore" about running an old ass game at 1000 FPS with a modern card.

All it does is to waste resources and make the card work at it's hardest for no reason. It's no different than swapping a gear at a say, maximum, 6500 RPM on a car that revs 7000 per gear. You should keep it lower so that the hardware doesn't get excessively get stressed.

If the card is obviously way beyond the generation of the game you're playing, then you're best off, if possible, LIMITING frames/putting a frame lock on your end.

March 27, 2013 | 10:42 AM - Posted by Ryan Shrout

Vsync does cause a ton of other issues including input latency.

March 27, 2013 | 10:44 AM - Posted by Anon (not verified)

You've said this already in both the article and comments but you only talked about input latency.

What are those other issues?

March 27, 2013 | 10:52 AM - Posted by John Doe (not verified)

It makes the entire game laggy an unplayable depending on condition.

You can read up over that TweakGuides guy's site on Vsync.

March 27, 2013 | 11:09 AM - Posted by Josh Walrath

Some pretty fascinating implications about the entire game/rendering pipeline.  There are so many problems throughout, and the tradeoffs tend to impact each other in varyingly negative ways.  Seems like frames are essentially our biggest issue, but how do you get around that?  I had previously theorized that per pixel change in an asynchronous manner would solve a lot of these issues, but the performance needed for such a procedure is insane.  Essentially it becomes a massive particle model with a robust physics engine being the base of changes (movement, creation, destruction, etc.).

March 27, 2013 | 02:18 PM - Posted by Jason (not verified)

research voxels... the technology exists but is pretty far off.

March 27, 2013 | 05:44 PM - Posted by Anonymous (not verified)

Regarding per-pixel-updates: Check this out: https://www.youtube.com/watch?feature=player_embedded&v=pXZ33YoKu9w

It's obvious the result must be delivered in frames (no way around it with current monitor technology), but the engine in the vid clearly works differently from the usual by just putting the newly calculated pixels into the framebuffer that are ready by the time.

March 27, 2013 | 02:07 PM - Posted by bystander (not verified)

Due to many frames being forced to wait for the next vertical retrace mode, while others do not, it will result in some time metering issues. This can result in a form of stuttering.

March 29, 2013 | 02:49 AM - Posted by Anonymous (not verified)

hardcore gamer here play BF3 v-sync ON!

because:

1. My monitor (as 90% of us) is 60hz!
don't need the extra stress/heat/electric juice on card/system.

2. Fed up with frame tearing every time i turn around.

March 27, 2013 | 10:27 AM - Posted by Prodeous (not verified)

With regards to the Nvidia settings of v-sync, it seems that Addaptive (half refresh rate) was selected capping it at 30fps vs Addaptive which would cap at 60fps.

Was that on purpose?

March 27, 2013 | 10:31 AM - Posted by Noah Taylor (not verified)

I'm still interested to see what type of results you come up with when using amd crossfire with a program like afterburner's riva tuner to limit the fps to 60, which would seems to be everyone's preference for this situation.

March 27, 2013 | 10:42 AM - Posted by Ryan Shrout

I think you'll find the same problems that crop up with Vsync enabled.

March 27, 2013 | 11:14 AM - Posted by Noah Taylor (not verified)

I have to admit observed FPS graphs are DAMNING to AMD, and I own 2 7970s and 7950s so I'm not remotely biased against them in any way. One thing i did notice is that dropped frames don't effect every game so hopefully this is something AMD may be able to potentially mitigate through driver tweaks.

I have to admit, crysis 3 can be a sloppy affair in AMD crossfire and now I can see exactly what I'm experiencing without trying to make guesswork out of it.

Regardless, the bottom line EVERYONE should take away from this, is that crossfire DOES NOT function as intended whatsoever, and we can now actually say AMD is deceptive in their marketing as well, this is taken directly from AMD's website advertising crossfire:

"Tired of dropping frames instead of opponents? Find a CrossFire™-certified graphics configuration that’s right for you."

They have built their business on a faulty product and every crossfire owner should speak up so that AMD makes the changes they have control over to FIX a BROKEN system.

March 27, 2013 | 11:17 AM - Posted by Josh Walrath

Just think how bad a X1900 CrossFire Edition setup would do here...  I think Ryan should dig up those cards and test them!

March 27, 2013 | 11:49 AM - Posted by SB48 (not verified)

I wonder if that one of the reasons why AMD never really released the 7990,
also if this was already a obvious problem with the 3870 X2...
or the previous gens card, like HD5000, 6000.

anyway, is there any input lag difference from NV to AMD (SLI-CF) without vsync?

also I would be curious to see some CPU comparison.

March 27, 2013 | 01:31 PM - Posted by John Doe (not verified)

I had both a dual 3870 and a dual 2900 setup, both were more or less the same thing.

Both has driven a CRT at 160HZ for Cube and both were silk smooth.

This is a recent issue. It has nothing to do with cards of that age. The major problem with those old cards was the lack of CrossFire application profiles. Before the beginning of 2010, you had absolutely no application profiles like you have with nVidia. So CF either worked or you had to change the game ".exe" names, which either worked or, made the game mess up or just kick you out of Steam servers due to VAC.

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