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| andy |
 Posted: Aug 23 2013, 06:27 AM |
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Advanced Member
Group: Members
Posts: 35
Member No.: 35896
Joined: 26-December 12
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[edit: I meant to say 59.94 throughout this post, including the title... oops!]
Soon I'll be in a magical fantasy land devoid of NTSC televisions, but I will have my US NES with me, along with my laptop, composite video USB capture device, and step-down transformer. Here's how I get beautiful 59.97 fps NES video, successfully prototyped at home:
1. Connect the capture device to the NES. I have the mono output from the NES split to the stereo inputs of my capture device via a Y-cable, and the composite video output goes straight to the composite video input.
2. Start VirtualDub 1.10.3 32-bit.
3. Select "Capture AVI" from the File menu to enter capture mode.
4. Select "Video Composite" in the Video Source submenu of the Video menu. This step may vary with capture device. You may also need to select your device in the Device menu. Plus you may want to tweak the levels using the "Levels" and "Histogram" items in the Video menu. I suggest adjusting the contrast until the curve has neither periodic spikes nor notches, then adjusting the brightness to minimize both underexposure and overexposure.
5. Select "Preview" in the Video menu. This enables software control over the video shown in the capture monitor window.
6. Select "Non-interlaced - field rate, even field first" in the Preview Acceleration submenu of the Video menu. This is necessary for the video to show up at 59.97 fps rather than 29.94 fps. If the video seems jerky, you could try fixing it by instead using "odd field first".
7. You may want to get a proper 4:3 aspect ratio, but monitors produced these days use weird ratios like 16:9, and VirtualDub doesn't seem to have an option to force an aspect ratio when the preview video is scaled to fullscreen (hint hint!). For my laptop, the solution was to create a custom video mode at 1200x900 (my screen's native resolution is 1600x900) and to turn off panel resizing (hotkey Ctrl+Alt+F11). Obviously, this step will vary wildly by computer.
Once I arrive at my destination, I'll see about connecting my laptop to a TV via HDMI, and I'll probably be able to coax it to 60 fps that way, even if it normally accepts only PAL.
Ooh! I should mention that this method outperforms my LCD TV's built-in deinterlacer which fails to notice that NES video is not truly NTSC but has somehow tweaked its timing such that the fields exactly overlap each other, producing 240p rather than 480i. This is easy to see in the comb-like artifact of moving or flashing objects. In the future I may just use my laptop as a deinterlacer rather and spare my TV the embarrassment.
Purists may complain that the NES 59.97 fps video doesn't match the graphics card and/or monitor running at 60 fps, resulting in one doubled frame in 2000, which is once every 33-1/3 seconds. I don't have a good solution for this, but your driver may let you pick non-integral frame rates. But consider that your 60Hz refresh rate is probably off a touch, and it's quite possible to get lucky and actually have 59.97Hz. An oscilloscope or frequency counter would be required to actually measure this. Aside: I've worked with video generation systems where the vertical refresh rate gradually oscillates, and the only reason we noticed was we had a special monitor (tiny head-mounted binocular CRTs designed to resemble NVG) that periodically blanked, corresponding with the rate dropping below 60Hz. Genlock was required to solve the problem.
These instructions probably also work for the SMS, SNES, Genesis, N64, PSX, and any other "240p" signal generators. One such example is the GameCube or Wii playing the original Metroid game found on the Metroid Prime disc after linking to a GBA with a completed Metroid Fusion game. I think the PS2 and maybe even PS3 will use this 240p mode when playing PlayStation 1 games. |
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| phaeron |
| Posted: Sep 8 2013, 07:10 PM |
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Virtualdub Developer
Group: Administrator
Posts: 7773
Member No.: 61
Joined: 30-July 02
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One gotcha when doing this is that the capture device isn't always consistent with the order in which it combines fields. I've seen cases where the capture device will suddenly switch polarity in the middle of the capture, which is of course annoying when trying to un-interlace the video.
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| andy |
 Posted: Sep 8 2013, 07:16 PM |
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Advanced Member
Group: Members
Posts: 35
Member No.: 35896
Joined: 26-December 12
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I also have trouble with the display going blank when switching to preview mode. Opening and closing VirtualDub popup windows sometimes seems to fix it, but only when all the coins lying on my desk are face up. And if I have just one coin face down, instead it bluescreens. Stupid driver. Totally random. Overlay mode works like a charm though. And no, I'm not forgetting to select the correct Preview Acceleration mode. |
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