30 progressive vs 60 interlaced capture card question

[marurun]

Hey, I have a question for those of you in-the-know about PC capture cards. I know NTSC video is 30 FPS interlaced, but when converted to digital it's just 30 FPS smashed together. Are there any digital capture cards that capture NTSC analog output as a 60 fps interlaced format? I ask because I'm kind of interested in exploring recording classic games from hardware, but doing it on the cheap. I don't want a $100 capture box that only reads HDMI after it's been fed through a Framemeister. Is there an affordable way to capture proper interlaced NTSC video in a way that preserves its unique characteristics?

[pierrot]

I may not entirely understand the question. Just to clarify, are you primarily trying to capture footage from consoles like the PS2, and a few others, with a number of games that don't offer video output in a progressive format--or in the case of the Saturn, have a higher resolution mode that is only output in an interlaced format? Outside of legacy capture cards, that have recording settings with low-resolution interlaced options, I don't see much way of preserving interlaced footage. You could probably use something like Handbreak to convert the video into 1080i from there, perhaps, but I don't know as that would meet your desired result.

Usually people are trying to convert interlaced video into progressive video, with the least number of artifacts possible, but I get the sense you're trying to do something most people wouldn't think of. Have I completely misinterpreted what you were going for?

[marurun]

Basically, a lot of analog video capture of video games breaks because things that flicker at 60 FPS don't display in a flattened video file running at 30 FPS. Most analog capture cards only capture 30 FPS. But technically, interlaced analog video is really 60 FPS, not 30 FPS, and your eyes do the compositing of the interlaced image. The reason why this is technically an image is that digital 30 FPS files don't properly display console 60 FPS flicker effects, either making objects solid or disappear. I'm wondering if there's any way to capture the actual interlaced analog output at 60 FPS with an affordable capture card rather than capturing it at 30 FPS with the interlacing kind of flattened into a fake progressive image.

[pierrot]

Oh, it seems like you're worried about aliasing, then (the classic example being the shield in Sonic games)? This is more an issue of sample rate. Nyquist's theorem states that to preserve a signal's integrity, it must be sampled at twice the greatest frequency of interest. If, for instance, it were just an asset being updated at half the rate of a screen refresh, with the screen refresh being 60Hz, the sample rate would also have to be 60 samples/sec.

It might be possible to achieve something similar by breaking up 30Hz progressive games into fields for 60Hz interlaced video, but that's probably asking too much of most capture cards, and probably not a solution for 60Hz games. The more ideal solution might be to get a capture card that can record 60Hz progressive video.

[marurun]

No, that's not it. I'm having trouble explaining, but basically older consoles, even over composite NTSC, are attempting to update the display 60 times per second (even if game logic is not updating that quickly). Most flicker effects on sprites would turn the display characteristic for a sprite on and off every frame, and on a regular NTSC TV it would appear like objects were flickery and semi-transparent (I'm not talking about the Genesis "screen door" transparency effect). In Contra, for example, when you hit the sprite limit, the game would make your machine gun bullets flicker on and off to make sure you could still see all the sprites instead of having some just disappear for good. The problem is that when this video output is recorded over most analog video capture cards, it displays at a strict 30 FPS and the flicker effects are lost, meaning an object may display for a second and then disappear for a couple seconds, because you aren't getting half the frames.

Basically, older consoles output a kind of off-spec 240p, which NTSC tube TVs interpret just fine but digital circuitry like that in capture cards and LCD TVs have trouble with. They smoosh it to a strict 480i, which doesn't work well for games.

[pierrot]

Okay, I think I'm getting a clearer picture of what you mean. It still sounds to me like you're ultimately trying to avoid aliasing in the analog to digital video conversion process, but basically you're looking for a video capture card that preserves the NTSC format standard, right? I guess I'm just a little confused, because what you're saying is certainly true for NTSC video, but I was fairly certain that old "240p" consoles (or otherwise 15kHz RGB systems) simply update one field ~60 times per second, thus 'halving' the vertical resolution, and leaving scan lines from a perpetually blank secondary field. I'm not sure if I'm still missing something more nuanced in your desired application, though.

Have you looked into Elgato products at all? I guess, continuing from what I think it is you're trying to accomplish, assuming you were able to record in a standard NTSC video format, the resulting interlaced video is still probably subject to the DSP algorithms inherent in the video card. I found some products from Osprey Video that are marketed as "Analog Capture Cards," which do seem like the closest thing I've seen to matching what you're looking for, but also aren't especially cheap, and probably aren't designed with this kind of application in mind.

[marurun]

Most digital captures of analog video generate 30 frames per second video files, meaning they're either not capturing every other field or they're combining fields into a single frame. Either way, I want a low-cost solution (cheaper than Elgato) that will properly capture the lower resolution 60 FPS output of classic consoles.

[pierrot]

Hmmm, I don't really know the entire landscape for the capture card market very well, so I'll defer to others who might have more wisdom in that area, before I exhaust all of your patience with me.

One last, potential, option I had come across is the Roxio Game Capture HD: https://www.roxio.com/enu/products/game-capture/hd-pro/overview.html. It seems to offer 1080i / 60 recording mode, at least. Apparently it was on sale on Amazon for $35 at some point. It only offers component and hdmi inputs, though. Also, the recordings I've seen with it look a bit unpleasant in terms of picture, but if you tool with the settings enough, maybe it could look pretty decent.

[Anapan]

The problem you seem to be having is mostly about deinterlacing. The capture cards I have the most experience with only capture raw video and as such they preserve all interlacing. It's up to you how to post-process the video to make it progressive. The reason those scalers and de-interlacers cost a lot of money is they have programs running on FPGA CPUs real-time-deinterlacing and transcoding the output into another format. It is possible to get the same product with any capture card, but it's done after recording, with a chain of post-processing filters to line-double the 29.97 FPS interlaced NTSC video to 60 Progressive, then clean it, and scale it back to 240P. In the case of the Framemeister, it's also doing some lowpass filtering, and scaling at the least, and it's advanced functions are truly impressive for near-realtime processing.
In old console video games, the signal is 15khz 240P @ 60 FPS, which is then converted to NTSC interlaced 29.970 FPS. The signal sent to a CRT TV to make it progressive with prominent scanlines is not part of the NTSC standard/specifications, which explains why most modern displays handle it so badly.
It's not a simple problem, but in the past I've been able to record the interlaced signal directly to my hard drive, and then use video editing software to recreate the 60FPS signal using a chain of filters. I'm sure that the technology is far beyond that method, but at the same time I bet a BT8X8 capture card is very cheap (I'd be happy to send you one for cost of shipping), and I can probably dig up my old AVISynth & VirtualDubMod video processing chains.
I got some spectacular recordings from Saturn S-Video after building a video chain to tweak the raw video's horizontal to remove all the artefacting and color fringing. The output was really close to 1:1 from an emulator.