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  1. Here is a loopy idea.

    Has anyone tried to emulate a NTSC encoder in software, or is anyone familiar with an effort to do so?

    The next question is, why? I dunno, just something to do. Here in the U.S., there are still low-power TV stations broadcasting in analog NTSC.

    It's easy to convert RGB into luminance using NTSC coefficients, but to be a true emulation you would need to synthesize a subcarrier.
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  2. there is workflows around for about 20 years,
    they might take VHS, if they still take them,
    or NTSC DV tape, you can use some NLE like Magix Vegas,
    they might take some appropriate mpg as a file, you'd need to ask for specs, but if you encode it with Magix Vegas, there should be no problem, these files could be easily tested on a distance

    before exporting in Vegas (or other NLE) just use some broadcast colors effect, (7.5 IRE, or custom luma, chroma, composite) or even to 16-235 RGB (Vegas can apply this) , audio balanced with a desired -6dB or something, 48000Hz.
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  3. NTSC is as good as obsolete. I can't imagine Vegas or any NLE program supporting it because the output would be basically useless; it wouldn't be compatible with anything. The few low-power TV stations still broadcasting analog NTSC probably use hardware encoders, just like the old days.

    There are people in this world who restore steam locomotives and vacuum tube radios as hobby projects, and they enjoy it. You wouldn't run a railroad with steam locomotives in revenue service in this day and age, though.
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  4. Originally Posted by chris319 View Post
    NTSC is as good as obsolete. I can't imagine Vegas or any NLE program supporting it because the output would be basically useless; it wouldn't be compatible with anything. The few low-power TV stations still broadcasting analog NTSC probably use hardware encoders, just like the old days.
    I guess folks who handed over those tapes, VHS or lately digital files for those studios with old equipment did not know it was useless. And those studios broadcasted those footage's were not aware that useless tools were used.
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  5. What do VHS tapes have to do with the topic at hand?

    Digital files? We didn't have digital files in 1970. It's 2020 now. In 2020 NTSC is a dinosaur.
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  6. What the heck are you talking about? What NTSC encoder even means?
    You want to emulate something from 1960 before digital era with those analog rules? I just told you, you take a video and then throw a bunch of filters on it to simulate NTSC. Am I in Twilight Zone or something? In 1960 you had recording in analog to tape and broadcasted it was as such with specific hardware with bunch of knobs turning left and right making a signal out of it and receiving it and specific viewing CRT at the end also equipped with bunch of knobs. What part of it do you wish to simulate? Just one part of it at the end, receiving signal? How? It was analog.
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  7. I got the NTSC encoder working except for interlace.

    I had thought about synthesizing a subcarrier but the math is way over my head. Much simpler to use the equations from Poynton.
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  8. I found the following to convert YIQ to a composite NTSC signal. It was in SMPTE 170M - 2004.

    Anybody want to take a crack at converting this back to YIQ? The math is way over my head. This is a "just for fun" project so don't knock yourself out.

    Code:
    double N = (0.925 * Y + 7.5 + 0.925 * Q * Sin(2 * PI * fsct + 33)) + (0.925 * I * Cos (2 * PI * fsct + 33))
    double fsct = 5 * 63/88 //3.579545455 COLOR SUBCARRIER FREQUENCY

    // RGB to YIQ
    double Y = R * 0.299 + G * 0.587 + B * 0.114
    double I = (0.5959 * R) - (0.2746 * G) - ( 0.3213 * B)
    double Q = (0.2115 * R) - (0.5227 * G) + (0.3112 * B)

    // YIQ to RGB
    double R = Y + 0.955986*I + 0.620825 * Q
    double G = Y - 0.272013 * I - 0.647204 * Q
    double B = Y - 1.106740 * I + 1.704230 * Q
    Last edited by chris319; 26th Jul 2020 at 21:24.
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  9. If you want to synthesize NTSC (which has absolutely nothing to do with VHS) yes, you can do it in software but the result is a digital stream anyway. You still have to convert it back to analog using a fast DAC so it becomes rather pointless when there are cheap hardware solutions that can directly convert RGB or YUV costing only a few $$. You would be emulating an IC like the AD720 series in software. If you really want to try it, the first place to search is for VHDL models of the AD72x series as these will have most of the math in them already.

    Brian.
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  10. Hi Brian -

    I don't know where you got the notion of VHS tapes or hardware. This is strictly a software emulation at a cost of 0. I already have it encoding Y, I and Q. That was the easy part.

    Theoretically I am generating the composite signal "N"; I just don't know how to decode it back to YIQ.
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  11. Member dellsam34's Avatar
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    Most software output NTSC as 720x480, NTSC broadcast standard is Nx525, N is the frequency of the luma carrier of each scan line in the raster including all the sync signals, So if you intend to broadcast it, it has to be converted to analog first which defeats the purpose of having it in digital in the first place when you can feed the pure digital video to the NTSC encoder and do both the DAC and NTSC standardisation in one step.

    I recall one of the members here was able to capture the full VHS frame in 780x525 or something like that, I don't know how he did it, try to find that sample and see if you can reverse it, Though VHS and live broadcast feed are two different things.
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  12. No VHS, no hardware, no broadcast. Just a software emulation.
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  13. Member Cornucopia's Avatar
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    Is this an academic exercise?

    Otherwise what's the purpose? Capturing a CVBS or RF input using a generic scientific sampler/a-to-d has uses in bringing in difficult-to-otherwise-capture material (due to corruption, deterioration, etc) to perform complex DSP that goes beyond what is feasible in the analog or hardware realms. Ultimately, those would hopefully be further decoded into normal (aka standards-based) digital video files. (Btw, those are still in a state not quite ready to rival normal methods)

    But to go the other direction WHILE emulating would require either an additional round-trip of decoding prior to normal (digital, digital-to-analog) output, or it would require being output using a similar (comparable but reverse direction) generic scientific d-to-a device (theoretically possible but I've never seen on). Plus storage of the emulated version would be much higher requirements.
    And to emulate for some other reason?


    Scott
    Last edited by Cornucopia; 3rd Aug 2020 at 21:58.
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  14. Not academic, just for fun.

    No hardware.
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