[yoshiyukiblade]

Just a heads up for anyone looking to get an Elgato Cam Link for capture: the original was discontinued and a 4k version took its place. It’s still the same price, but apparently it’s quite different under the hood. It only outputs 4:2:0 according to sources I’ve read. OBS still reports YUY2 on my end, but I see artifacts when point resizing vertically, which implies chroma subsampling occurring in that direction. This can be remedied by using bilinear resizing instead, but it can’t hide all the artifacts.

It looks like the chroma subsampling method used on the new Cam Link is not easily reversible in OBS. With the old version, you can simply point resize to a lower resolution to recover perfect pixels since the OSSC does integer multiplication vertically and horizontally (in optim. modes). This method doesn’t work quite as well with the new version: https://i.imgur.com/oZc6nbc.png Notice the artifact on the right side of the pink boxes. I get the general impression that the colors aren’t quite aligned the way they should be.

Also, it looks like the matrix and range for the Cam Link 4k is Rec. 601, Partial. The old version was Rec. 709, Full.

[yoshiyukiblade]

The Elgato Cam Link doesn’t seem to capture the new 512×240 optim. mode properly; it looks like there’s a sync glitch every 1-5 seconds: https://i.imgur.com/R4882TE.png

The output to my PC CRT monitor looks perfectly fine though, but I haven’t been able to find any tweaks to stabilize it for capture. Previously, my preferred capture method was a pseudo 512×480 optim. mode, by using 320×240 optim. and upping the H sample rate to 682 (among other adjustments). The limitation was that it could go only as far as 510 H active pixels, but it was a stable image. In the end, it is effectively one vertical column of pixels lost in terms of normal 256×240 modes. I’ll have to stay with with that method for now.

[yoshiyukiblade]

I experimented with this briefly in the past. What I did was I bought a composite/S-video to component/RGsB (sync on green) converter to get the OSSC to recognize the signal. The OSSC can take RGsB from the component inputs. The problem is, like you experienced, it loses sync frequently. I think something like a time base corrector (TBC) might address that problem and output a cleaner picture, but I’m not curious enough to spend over $300 to experiment with it! Maybe I’ll find a used one for cheap some day, but in any case, losing sync was also one of the major issues I ran into during testing.

[yoshiyukiblade]

This is definitely a nice option to include in the firmware. I don’t have a 1CHIP SNES to test it on, but I did mess around with it a bit on my older model SNES. My unit seems to output a weak signal. Working backwards from the equation in James-F’s post, it would have to be under 0.65 V for the peak input. Pushing the coarse gain to 1.4 appeared to be fine, but 1.5 showed signs of clipping, even if it should theoretically be OK (less than 1.0 after multiplication). A pure white screen isn’t at 255 at the output either. I’m not sure why that is, but I’ve been basing the output values off of lossless RGB recordings made in OBS, so anything along that video chain may affect the final output.

Interestingly, I found no immediately-visible differences between high coarse/low fine gain vs low coarse/high fine gain. I tested coarse gains at 0.8 and 1.4, saving each setting to their own profiles and switching between them; they looked pretty much the same to me. I was assuming that pushing analog gain close to 1.0 would be most optimal, similar to “exposing to the right” (ETTR) in digital photography, but it doesn’t make much of a difference in the end.

On a side note, the output video on the test firmware was odd. The best way I can describe it is that it was outputting 4:2:2 or something. Optim. mode colors were not clean, but the resolution was fine, judging from the black-and-white checkerboard pattern in the 240p test suite. I could kind of salvage the video output by sampling at 682 and setting the active area to 512, but it’s not as good as it should be.

That’s all for now. Thanks paulb_nl for providing us with a test build!

[yoshiyukiblade]

Thanks paulb_nl. It looks like the changes allowed for a larger H. active area for 320×240 optim. mode.

I found a quirk that normally doesn’t appear when using generic scaling, and it’s related to setting the active area well above 512 while keeping the sample rate fixed at 682. I guess a screenshot would best illustrate this problem (point scaled up to 2208×1568): https://i.imgur.com/5eILBOx.png

In this case, I set the active area to 552 (Cam Link outputs to 1104×480). Normally, the H. active area will just expand to have more open black space on the right-hand-side of the video, allowing for backporch adjustments to move the image to the right. However, it looks like the extra space on the right-hand-side is a copy of a portion of the SNES active area. The right side of the video gets cut off as I increase the backporch, so there’s an invisible barrier and I have to keep the image as far left as possible. I don’t know if its just a problem with the Cam Link, but I figured it was worth mentioning. Other than that, it works nicely when scaled down to 256×240.

[yoshiyukiblade]

Certainly, I would be happy to give it a try. Interesting that it did 4×512 multiplication. With H. active at 510, the Cam Link showed a resolution of 1020×480, which is just 2x.

[yoshiyukiblade]

Thanks for the suggestion paulb_nl! I attempted this on 256×240 optim. a while back with no luck and didn’t consider trying it in 320×240 optim. The method almost works, but I lose picture at exactly H. active 512. My CRT can display 511 fine, but the capture card doesn’t like it. H. active 510 works for both outputs, but that’s a net 1 pixel loss for 256×240 content (and I prefer shifting the image to the right 1 pixel and crop the left border, so that’s a net 2 pixel loss).

Unlike the generic scaler, turning on AV3 interlacefix didn’t allow for higher horizontal resolutions, and I’m not sure what other options I can tweak to make it work. What I see looks good though, and it suits my preferences at the moment.

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