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VGA Capture Thread

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Reply 840 of 1000, by darry

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I just had an idea and tested it.
What if I started Doom, connected the VGA card (Voodoo 3 for testing) into an OSSC, set the OSSC to passthrough 400 line mode (640x400 sampling) and connected it to an Elgato Cam Link 4K ?

IT WORKS!

I can see and capture footage at 640x400@70Hz of Doom using Virtualdub .

I then set the OSSC to 720x400 sampling (text mode), reset the Cam Link 4K and tried to capture a random text mode .

IT ALSO WORKED!

Footage was captured at 720x400@70Hz .

The only allowed colourspace was YUY2, but it still looks fine, IMHO .

I will try to post some actual captures soon .

EDIT: Since the Cam Link 4K accepts 640x400@70Hz and 720x400@70Hz over HDMI , I strongly suspect that using an Nvidia card (for example) with DVI output and an HDMI/DVI EDID emulator to force 640x400@70Hz and 720x400@70Hz would be possible . At his time, I will not be testing that (my EDID emulators are already in use), however .

Reply 841 of 1000, by darry

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darry wrote on 2020-09-04, 20:34:
I just had an idea and tested it. What if I started Doom, connected the VGA card (Voodoo 3 for testing) into an OSSC, set the OS […]
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I just had an idea and tested it.
What if I started Doom, connected the VGA card (Voodoo 3 for testing) into an OSSC, set the OSSC to passthrough 400 line mode (640x400 sampling) and connected it to an Elgato Cam Link 4K ?

IT WORKS!

I can see and capture footage at 640x400@70Hz of Doom using Virtualdub .

I then set the OSSC to 720x400 sampling (text mode), reset the Cam Link 4K and tried to capture a random text mode .

IT ALSO WORKED!

Footage was captured at 720x400@70Hz .

The only allowed colourspace was YUY2, but it still looks fine, IMHO .

I will try to post some actual captures soon .

EDIT: Since the Cam Link 4K accepts 640x400@70Hz and 720x400@70Hz over HDMI , I strongly suspect that using an Nvidia card (for example) with DVI output and an HDMI/DVI EDID emulator to force 640x400@70Hz and 720x400@70Hz would be possible . At his time, I will not be testing that (my EDID emulators are already in use), however .

I may have spoken too soon about the quality . Having to use YUY 4:2:2 instead of 4:4:4 or RGB24 does not make the text example look all that good .
Considering there is firmware exploration work being done on Cam Link 4K, maybe a non sub-sampled mode could be added .

640x400

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720x400

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EDIT : Before anyone asks, OSSC line2x modes are not recognized by the Cam Link 4K . Also, none of the Elgato capture software works at 70Hz. Virtualdub or Virtualdub2 work fine, though .

Last edited by darry on 2020-09-05, 01:42. Edited 1 time in total.

Reply 842 of 1000, by darry

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Good news, I was wrong . The Cam Link 4K does manage to capture 1280x800@70Hz and 1440x800@70Hz as line-doubled by the OSSC , so the YUY2 issue is essentially a non issue now, if you have an OSSC .

1280x800

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1440x800

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Reply 843 of 1000, by darry

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A short (less than 40MB) video of a capture (line-doubled to 1280x800@70Hz) of Doom in attract mode . It is compressed using h.264 at a max of 6Mbps, but should give a good idea . The intermediate capture codec was Lagarith .

https://file.io/QNdqG3fTEfiH

https://filebin.net/k5ndvgs3pf3ovj92 should be OK for 1 week .

https://easyupload.io/aeo4bg should be OK for 30 days .

Last edited by darry on 2020-09-05, 01:24. Edited 1 time in total.

Reply 845 of 1000, by darry

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MAZter wrote on 2020-09-05, 01:18:
: https://i.postimg.cc/nzvhsfM1/Screenshot-8.png […]
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darry wrote on 2020-09-05, 01:10:

:
Screenshot-8.png

DOH!

https://filebin.net/k5ndvgs3pf3ovj92 should be OK for 1 week .

EDIT : https://easyupload.io/aeo4bg should be OK for 30 days .

Reply 846 of 1000, by darry

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The Cam Link 4K also handles 1600x1200@70Hz with reduced blanking as generated by a Geforce FX 5900 that was booted connected to an EDID emulator . (See this thread for details 70Hz in pure DOS at 1600x1200 (or other) over DVI on an old card (FX5900) with modern monitor is possible ).

Notice the extremely soft Nvidia scaling on this card .

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EDIT: Before anyone asks, no it isn't any sharper if I leave it at 60Hz .

Reply 847 of 1000, by darry

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Looking at text capture at 720x400 in post Re: VGA Capture Thread, and having read some stuff on videogameperfection.com forums, I am starting to wonder if the Cam Link 4K is actually capturing 4:2:2, as it says it is or whether it might actually be capturing 4:2:0 and upsampling chroma to 4:2:2 on output .

Anybody here good enough with this stuff to detect this visually from the capture ? Otherwise, anybody have any suggestions on how best to test this ?

I have tried using Virtualdub to resize the 1440x800 version to 720x400 using nearest neighbour and then selectively converting to 4:2:2 or 4:2:0 , but even 4:2:0 doesn't look as bad as the original 720x400 capture .

EDIT : I know Virtualdub works in RGB internally, so maybe it's 4:2:0 to full RGB conversion/upscaling is actually better than the Cam Link 4K's internal conversion from whatever it captures at to 4:2:2 ?

EDIT2: I think I may have upgraded the Cam Link 4K's firmware after the first 720x400 text capture, so I should probably redo a text capture at 720x400 .

EDIT3 : Retested it, and it does seem better, but still not that great . The original test was a screen capture the preview windows whereas this one is an actual frame export .

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EDIT4 : On second comparison, pretty much identical .

EDIT5 : Even if I convert the 2: nearest neighbour downscaled 1440x80-->720x400 version through a 4:2:0 subsampling followed, by 4:2:2 , followed by RGB conversion still does not give as bad a result as the 720x400 direct capture . Anyway, since capturing in line2x mode seems to negate to negate the effects of the subsampling, DOS VGA modes should be OK .

Reply 848 of 1000, by vvbee

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Image quality comparison between the Datapath VisionRGB-E1S and the Datapath VisionRGB-PRO2.

Captured at 640 x 480 from a Matrox G400 with a normal-quality VGA cable using the VCS software.

The base image quality is virtually the same. Any variation appears to be largely or entirely due to user-adjustable parameters like color balance, brightness, and contrast.

The first image is the E1S (captured in 2020), the second image is the PRO2 (captured in 2019). Also some magnified details, in that order.

visionrgb-e1s.png
visionrgb-pro2.png

visionrgb-e1s-clock.png
visionrgb-pro-clock.png

visionrgb-e1s-my-computer.png
visionrgb-pro-my-computer.png

Reply 849 of 1000, by darry

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vvbee wrote on 2020-09-07, 12:50:
Image quality comparison between the Datapath VisionRGB-E1S and the Datapath VisionRGB-PRO2. […]
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Image quality comparison between the Datapath VisionRGB-E1S and the Datapath VisionRGB-PRO2.

Captured at 640 x 480 from a Matrox G400 with a normal-quality VGA cable using the VCS software.

The base image quality is virtually the same. Any variation appears to be largely or entirely due to user-adjustable parameters like color balance, brightness, and contrast.

The first image is the E1S (captured in 2020), the second image is the PRO2 (captured in 2019). Also some magnified details, in that order.

visionrgb-e1s.png
visionrgb-pro2.png

visionrgb-e1s-clock.png
visionrgb-pro-clock.png

visionrgb-e1s-my-computer.png
visionrgb-pro-my-computer.png

Cam Link 4K is definitely worse than the Datapath (which is essentially perfect). Even OSSC Line2x input into it has visible chroma issues if you look close enough with the Cam Link 4K . OSSC output is fine on the monitor, even under a magnifying glass . If only someone could mod the Cam Link 4K to do RGB or at least YUV 4:4:4 .

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EDIT: I may need to try something else for capturing, or at least for generating PNGs . Instead of exporting a PNG in Virtualdub2, I did it in MPC-HC . It's chroma upsampling is different and, IMHO, better .

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EDIT2: Looks like it's the PNG export function in Virtualdub2 is buggy in that it does a relatively bad job at RGB conversion. Using the Virtualdub2 resize filter to do nearest neighbor integer upscaling and looking at preview pane, the image looks much closer to the MPC-HC export . I imagine Virtualdub2 uses different algorithms for its internal chroma upsampling vs PNG export .

Reply 850 of 1000, by Renaissance 2K

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vvbee wrote on 2020-09-07, 12:50:

Image quality comparison between the Datapath VisionRGB-E1S and the Datapath VisionRGB-PRO2.

Captured at 640 x 480 from a Matrox G400 with a normal-quality VGA cable using the VCS software.

Do you have a link to the cable you're using? I have an E1S and want to capture from VGA, but most of the cables on Amazon are openly unidirectional - DVI to VGA - and the ones I've bought that aren't up front about it mention the limitation once you open the pack.

Reply 851 of 1000, by appiah4

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Renaissance 2K wrote on 2020-09-08, 05:56:
vvbee wrote on 2020-09-07, 12:50:

Image quality comparison between the Datapath VisionRGB-E1S and the Datapath VisionRGB-PRO2.

Captured at 640 x 480 from a Matrox G400 with a normal-quality VGA cable using the VCS software.

Do you have a link to the cable you're using? I have an E1S and want to capture from VGA, but most of the cables on Amazon are openly unidirectional - DVI to VGA - and the ones I've bought that aren't up front about it mention the limitation once you open the pack.

Wouldn't VGA to DVI require an active conversion anyway? DVI-I has an anologue signal that is easy to wire up to a VGA connector but you can't just translate analogue VGA signal to a digital DVI input (as most units with DVI inputs do not accept analogue input from the DVI port regardless of connector type).

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Reply 852 of 1000, by vvbee

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Renaissance 2K wrote on 2020-09-08, 05:56:

Do you have a link to the cable you're using? I have an E1S and want to capture from VGA, but most of the cables on Amazon are openly unidirectional - DVI to VGA - and the ones I've bought that aren't up front about it mention the limitation once you open the pack.

Using a passive DVI to VGA converter and a second-hand VGA cable, specs unknown. The capture card's input is both analog and digital, so I suppose as long as you have an analog-capable passive DVI to VGA converter, it should work.

Reply 853 of 1000, by Tree Wyrm

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You can feed either digital or analog signal to Datapath cards with DVI input, no need for any special cables, just a decent VGA cable and passive converter to DVI-I. Might get confusing if video card has both analog and digital video output through DVI, in which case it will default to digital signal.

Pretty much my setup with E2S (dual input version of E1S). I've since sold my upscalers and converters, except OSSC for consoles. Lag is minimal, comfortable to play action games, and vvbee's VCS is a must have for Datapath cards.

Reply 854 of 1000, by darry

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A question to Datapath E1S owners . Up to which resolution or pixel clock do these cards handle RGB 888 capture ? The docs I have found seem a bit unclear to me on that point .

It does say
"Maximum analog RGB video capture resolution of 2048x1536 x24bit
Maximum DVI capture resolution of 1920x1200 x24bit"
on the website, but I want to be sure that explicitly refers to actual capture data and not just "max accepted input" during capture .

EDIT : If someone can suggest a USB alternative that can handle standard VGA modes (including 70Hz ones) and the usual VESA SVGA modes up to at least 1600x1200@60Hz, does RGB 888 or at least YUV444 capture and costs less than 200 US$, that would be even better for me .
EDIT2: Either VGA input or DVI is fine .

Reply 855 of 1000, by maxtherabbit

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Darry, get a datapath from ebay. They come up for around $60US frequently. AFAIK that analog bandwidth spec is correct for the E1S. The E1 is lower

Reply 856 of 1000, by darry

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maxtherabbit wrote on 2020-09-10, 14:39:

Darry, get a datapath from ebay. They come up for around $60US frequently. AFAIK that analog bandwidth spec is correct for the E1S. The E1 is lower

Thank you . I will wait for an inexpensive E1S . I am not in any hurry.

EDIT : E1S has been ordered . If only there was an affordable RGB capable USB alternative .

EDIT2 : TBH, if someone just wants to capture footage that will end up in YV12 and lossily compressed anyway, the YUY2 of the Cam Link 4K along with an OSSC are perfectly fine, maybe even for pro use (IMHO opinion) . I have seen captured video that looked a lot worse on Youtube .

Reply 857 of 1000, by NJRoadfan

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The Datapath E1S is a proper 4:4:4 RGB capable frame grabber. You want to avoid chroma subsampling as much as you can in your processing chain as every conversion step will result in further degradation of color. You also have to deal with potential errors from color space conversions between RGB and YUV (Rec.601 or Rec.709, some cards screw it up in hardware). Also important if you are using an OSSC in passthru is to make sure the sampling and dot clock are properly tuned.

Best way to test for chroma subsampling errors is to use the same example as wikipedia, red text on a green background.

Reply 858 of 1000, by darry

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NJRoadfan wrote on 2020-09-13, 18:54:

The Datapath E1S is a proper 4:4:4 RGB capable frame grabber. You want to avoid chroma subsampling as much as you can in your processing chain as every conversion step will result in further degradation of color. You also have to deal with potential errors from color space conversions between RGB and YUV (Rec.601 or Rec.709, some cards screw it up in hardware). Also important if you are using an OSSC in passthru is to make sure the sampling and dot clock are properly tuned.

Best way to test for chroma subsampling errors is to use the same example as wikipedia, red text on a green background.

Thank you for your input .
I understand the need to avoid sub-sampling as much as possible, especially when dealing with computer graphics with hard edges . As for color space conversions, I can force the OSSC to RGB output, but it looks as though it defaults to that anyway . The reason I am using OSSC in line2x mode rather than passthru when capturing with the Cam Link 4K is that the line-doubling minimizes the appearance of the YUY2 sub-sampling artifacts (if adjacent pixels have the same chroma value, the interpolated value should match the original one, as long as alignment matches, as far as I understand it) .

Reply 859 of 1000, by swaaye

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I got out the Avermedia C127 (Game Broadcaster HD) that I bought around 8 years ago and found its VGA input is now purple-shifted. I guess there is damage somewhere on the card but I can't see it. I tried different cables, VGA cards, drivers and even different PCs for the capture card (plus Win7 vs 10). HDMI/DVI capture still works though.

That card did have problems with resolutions under 640x480 though.

It sounds like the Datapath E1S is the way to go now?