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  1. This is a bit off topic as it is about analog video broadcasting, rather than digital, but this is the only section on the whole forum that has anything to do with professional video broadcasting of any kind, so this is where I'm going to put the thread (there should be a section on analog TV tech, for legacy video technology discussions, but there isn't, so this is where my thread is going to go, unless a moderator moves it somewhere else).

    I've noticed that the officially stated number number of TV lines in an NTSC signal is in fact 525. But every video-input card that can receive a TV signal, or connect to a camcorder, says it records 720x480 video, rather than 720x525 video. Why? Why do all the devices that I've ever read about always ignore 45 lines of the image? Same issue goes for PAL. Everything I've seen for PAL video is that it's 720x576. However if you look at places that inform you of the official PAL specs, you will see it's supposed to be 625 lines (not 576). It appears that most PAL equipment is ignoring 49 lines of the image. Why is this? Can somebody please explain?

    And on a related note, since NTSC doesn't support more than 525 lines (assuming that there is any way to make a TV set, or video input card on a computer, display all 525 of them), how in the world do they make video cameras like this one (which is an NTSC based analog security camera) http://www.amazon.com//dp/B006VXWQ9S/ claiming to output 700 lines? NTSC doesn't support 700 lines. Even PAL doesn't support that many lines. Is this a case of false advertising? Or is this some proprietary NTSC-based standard that doesn't comply with "pure" NTSC standards? Is it designed to only be viewed on certain specialized equipment that is capable of handling more lines than would be allowed under official NTSC standards?
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  2. Member Cornucopia's Avatar
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    #1 Those lines = signal total. Signal = Image + Blanking (scan line V + H reset) & sync. Those extra blanking/sync lines are needed in the analog world, but digital coding handles that automatically behind the scenes, so is superfluous/unnecessary.Therefore, capture apps/devices ignore/drop them.

    #2 That Cam seems to be NTSC or PAL. The optics and sensor are capable of that resolution, but some must be lost when formatting for NTSC or PAL. So it is a bit of a marketing exaggeration.

    Scott
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  3. The 525 lines includes vertical sync* information (the black stripe above and below active image.) Active image is 486 lines, modified to 480 for digital. The 700 line resolution is a measure of horizontal resolution, how much discrete information there is along each of the 486 active image lines. Since it's analog there's no theoretical limit to horizontal resolution, although in reality anything over 800 was a special case.

    *(edit: oops, blanking, thanks, Scott.)
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  4. So is blanking the same thing as sync? When an analog TV set receives the signal for the start of a frame (or end of a previous frame) does it automatically perform blanking and frame sync? Or are these 2 separate signals? If they are 2 separate signals, which one corresponds to the extra image lines counted in the NTSC standard? Or do both contribute to the total line count? Does the inter-line time (electron beam scanning flyback time between lines) also count as extra lines (lets say that in total, the flyback time for all lines = the amount of time it takes to scan forward on 5 lines, would this contribute "5 lines" to the official total line count in the NTSC spec)? Or is it just the vertical flyback time (vertical blanking interval from the lower right of the screen back to the upper left of the screen) that is counted as these extra lines? Is the frame-sync signal sent during this time, or is it an additional time? If it is separate from the blanking, does the sync also count as part of the total number of "lines" in the NTSC signal?

    Is it possible to get digital video capture cards that will display/record all 525 lines, so that one can actually see what extra information is being broadcast in the unused lines (possibly as a TV signal diagnostic tool, even if not a standard receiver)? Are such devices that receive all 525 lines even made or sold anywhere? Personally I'm curious to see what extra information might be put in these extra lines in addition to normal blanking and sync signals. I'm guessing digital data for closed caption text is stored here, as well as any copyprotection data like Macrovision, possibly even metadata that stores information on the show being broadcast like the name of the TV station, name of the show, call-letters of the station, etc. Even though they don't broadcast analog TV anymore, I still have some old VHS tapes laying around, including some that are recordings of TV broadcasts like nightly news from many years ago, etc. These could be interesting signal sources to analyze, if I could find a USB composite video input card that I could connect a video to, if said USB composite video input devices (and corresponding drivers) in fact were allowed to send the WHOLE FRAME (including the extra lines, for a total of 525 lines) to be saved as an AVI file for later viewing. Anybody know if such USB devices exist, or even if PCI or PCIe devices exist that have this capability (and are not limited to recording only the normal 480 lines)? What website sells such devices (if such devices exist)? This could be a potentially very interesting thing to look into, with the right equipment.
    Last edited by Videogamer555; 3rd Mar 2015 at 18:12.
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    Originally Posted by Videogamer555 View Post
    Is it possible to get digital video capture cards that will display/record all 525 lines, so that one can actually see what extra information is being broadcast in the unused lines (possibly as a TV signal diagnostic tool, even if not a standard receiver)? Are such devices that receive all 525 lines even made or sold anywhere? Personally I'm curious to see what extra information might be put in these extra lines in addition to normal blanking and sync signals. I'm guessing digital data for closed caption text is stored here, as well as any copyprotection data like Macrovision, possibly even metadata that stores information on the show being broadcast like the name of the TV station, name of the show, call-letters of the station, etc. Even though they don't broadcast analog TV anymore, I still have some old VHS tapes laying around, including some that are recordings of TV broadcasts like nightly news from many years ago, etc. These could be interesting signal sources to analyze, if I could find a USB composite video input card that I could connect a video to, if said USB composite video input devices (and corresponding drivers) in fact were allowed to send the WHOLE FRAME (including the extra lines, for a total of 525 lines) to be saved as an AVI file for later viewing. Anybody know if such USB devices exist, or even if PCI or PCIe devices exist that have this capability (and are not limited to recording only the normal 480 lines)? What website sells such devices (if such devices exist)? This could be a potentially very interesting thing to look into, with the right equipment.
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    How is it a waste of time if you want to learn something you're interested in. (rhetorical question)


    @ Videogamer555

    This is what the non-picture parts of a PAL broadcast signal look like.*
    I made them visible using the H/V-Delay function of my Sony PVM monitor (professional production monitor).

    (* Actually it's not from a real analog transmission, it's the composite out of my DVB-S receiver.)




    You can see the sync pulses (both horizontal and vertical ones) which are blacker than video black. The brown column is the PAL color burst. The fuzzy stuff in the vertical blanking is the videotext.
    Last edited by Skiller; 3rd Mar 2015 at 20:14.
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  7. Originally Posted by Videogamer555 View Post
    Is it possible to get digital video capture cards that will display/record all 525 lines, so that one can actually see what extra information is being broadcast in the unused lines
    There's nothing but sync pulses in the extra lines. There were some capture cards that capture 486 lines (of which the first and last are only half lines because the NTSC picture is carried 485 lines) but I haven't seen any of those in a while.
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  8. Closed captions and vertical interval timecode (VITC) are optionally included in the vertical interval for NTSC. Macrovision signals are also in the vertical interval for VHS. That's about it as far as analog metadata. Additional information was simply included in head slates.

    If you have a cross-pulse or waveform monitor you can see what's there.
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  9. Member Cornucopia's Avatar
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    Let me try to explain it stepwise:

    1. The (black & white) analog TV signal can be thought of as a kind of Continuous Sine Wave. In 2 dimensions (H, V or height, width). This is what's known as a Lissajous signal. The voltage intensity of the ("now") instantaneous point of the wave corresponds with the luminance of that "pixel" (if mapped onto a digital grid).

    Click image for larger version

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    2. This Lissajous sine wave is NEVER exactly a horizontal line like we think it is/ought, it is a diagonal. ALL horizontal lines on a (old-school CRT) TV are actually slightly diagonal. Witness this succession of diagonals as they tend closer and closer to horizontal (only the LAST one is actually perfectly horizontal):

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    3. Through the majority of the wave's oscillation, it is BLANK (aka BLACK). This is known as "blanking" (duh!). Only during it's "active picture" stage does an image show.

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    4. The wave is more complex than this analogy, but for explanation's sake, think of the wave as free-running continuously, on it's own, in your display. Kind of like a FLYWHEEL. If the "flywheel" (oscillation) were perfect, you would just need to transmit the voltage corresponding to the luminance at the point where the wave's travel matches it's intended position onscreen. However, since no flywheel is truly perfect, the oscillating wave gets out of sync with the luminance voltages it's supposed to carry. So sync pulses are put in at each "reset" change in the signal to continually "correct" the timing. (Notice the position of the sync pulses in the pic above)

    (This is also why there needed to be manual sync fine tuning adjustments on old TVs, known as Vert & Horiz. Hold)

    5. Linearly over time, the signal looks more like this (this is 1 scanline's worth):

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    6. Complication: The presence of the sync pulses tells the oscillator to temporarily speed up so as to not waste as much time during the "hidden"/blank ("flyback") portion as during the active picture portion (otherwise there would be even LESS active picture, percentage-wise). Notice in the pic above the small time portion allotted to the blanking (seen as the "front porch" and the "back porch").

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    7. Color is tacked on as a modulation (usu. phase or freq. mod) of that luminance, where the modulation "steers" the color a certain multi-vector distance away from perfect/plain Black-Grey-White. Also continuous.

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    Scott
    Last edited by Cornucopia; 4th Mar 2015 at 14:21.
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  10. The analog raster scanning would more accurately be pictured as:

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    (Image taken from http://lea.hamradio.si/~s51kq/V-BAS.HTM)

    As you can see, the active picture includes only half of the top and bottom scan lines. Hence the active picture is contained in 485 lines. Computers like working with rectangular arrays. So when those 485 scan lines are captured (and stored) the first and last scan lines become full scan lines giving a total of 486 lines:

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    The green lines represent extra data that is captured (which is black) or filled in with black.
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    Originally Posted by Videogamer555 View Post
    Is it possible to get digital video capture cards that will display/record all 525 lines, so that one can actually see what extra information is being broadcast in the unused lines (possibly as a TV signal diagnostic tool, even if not a standard receiver)?
    The Arduino Video Experimenter might do what you want.
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  12. Member Cornucopia's Avatar
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    Originally Posted by JVRaines View Post
    Originally Posted by Videogamer555 View Post
    Is it possible to get digital video capture cards that will display/record all 525 lines, so that one can actually see what extra information is being broadcast in the unused lines (possibly as a TV signal diagnostic tool, even if not a standard receiver)?
    The Arduino Video Experimenter might do what you want.
    No, that device specifically mentions using a "sync separator" which is where it drops out the sync & blanking.

    There are generic scientific signal processing A/D converters out there, but they are not video-specific (hence "generic"). You'd want something that can take the 1V peak-to-peak signal (composite, component) and sample it at 13.5MHz (the standard SD ITU sampling rate) or higher. Likely higher if you wanted to include blanking & sync. ~Quadruple that for HD.

    But a big caveat reminder: you will just be getting a raw voltage fluctuation sampling - nothing shows up as discernible video that way (unless you do some MAJOR data processing after the fact). Interesting for scientists, but that's about it, and I don't recommend it, especially if you're just "curious".

    Scott

    @jagabo, yes that is cleaner and does include the upper & lower 1/2 lines, but I was trying to show the flyback as well.
    Last edited by Cornucopia; 4th Mar 2015 at 14:18.
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  13. Mountains of gear vaporeon800's Avatar
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    Originally Posted by Videogamer555 View Post
    Personally I'm curious to see what extra information might be put in these extra lines in addition to normal blanking and sync signals. I'm guessing digital data for closed caption text is stored here, as well as any copyprotection data like Macrovision, possibly even metadata that stores information on the show being broadcast like the name of the TV station, name of the show, call-letters of the station, etc.
    Just view my thread and save yourself the trouble.

    The one thing that I haven't seen mentioned here yet is VITS.
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  14. Originally Posted by vaporeon800 View Post
    Just view my thread and save yourself the trouble.
    Nice work. I hadn't seen that before.
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  15. Originally Posted by Videogamer555 View Post
    Is it possible to get digital video capture cards that will display/record all 525 lines, so that one can actually see what extra information is being broadcast in the unused lines (possibly as a TV signal diagnostic tool, even if not a standard receiver)? Are such devices that receive all 525 lines even made or sold anywhere? Personally I'm curious to see what extra information might be put in these extra lines in addition to normal blanking and sync signals. I'm guessing digital data for closed caption text is stored here, as well as any copyprotection data like Macrovision, possibly even metadata that stores information on the show being broadcast like the name of the TV station, name of the show, call-letters of the station, etc. Even though they don't broadcast analog TV anymore, I still have some old VHS tapes laying around, including some that are recordings of TV broadcasts like nightly news from many years ago, etc. These could be interesting signal sources to analyze, if I could find a USB composite video input card that I could connect a video to, if said USB composite video input devices (and corresponding drivers) in fact were allowed to send the WHOLE FRAME (including the extra lines, for a total of 525 lines) to be saved as an AVI file for later viewing. Anybody know if such USB devices exist, or even if PCI or PCIe devices exist that have this capability (and are not limited to recording only the normal 480 lines)? What website sells such devices (if such devices exist)? This could be a potentially very interesting thing to look into, with the right equipment.
    Some of capture chips support VBI capturing (at least Brooktree/Conexant and maybe Philips) - search for solution based on one of this vendors. Alternatively any general analog acquisition board with at least 15 - 20M samples per second is OK for your needs.
    Side to this there is nothing fancy in VBI for most people.

    And very important info - why they say 525 lines instead 480 (or different) - this is outcome of simple calculation = number of lines multiplied by picture rate (field rate divided by 2 i.e. Vertical sync frequency) gives us exactly Horizontal sync frequency so in case of NTSC color systems it is 525*(30000/1001)=15734.265734265734265734265734266Hz - as you see each number in video is directly related with other number.

    btw PAL like systems (or rather 50Hz) are 625 line systems (and usually when people says NTSC it means 525 lines color TV and when they say PAL this mean 625 lines).

    Forgot to mention that it is possible to sample video with audio card but bandwidth will be significantly reduced - less than 20kHz in most of cases, however this is perfectly sufficient to do processing on picture/field level (for example Dolby use this approach to measure lipsync).
    Last edited by pandy; 11th Mar 2015 at 08:12.
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  16. Video Restorer lordsmurf's Avatar
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    Complex explanation: ^ What they said.

    Easy explanation: Analog "lines" has nothing to do with digital video resolution.
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    Originally Posted by Videogamer555 View Post
    Is it possible to get digital video capture cards that will display/record all 525 lines, so that one can actually see what extra information is being broadcast in the unused lines (possibly as a TV signal diagnostic tool, even if not a standard receiver)? Are such devices that receive all 525 lines even made or sold anywhere? Personally I'm curious to see what extra information might be put in these extra lines in addition to normal blanking and sync signals. I'm guessing digital data for closed caption text is stored here, as well as any copyprotection data like Macrovision, possibly even metadata that stores information on the show being broadcast like the name of the TV station, name of the show, call-letters of the station, etc. Even though they don't broadcast analog TV anymore, I still have some old VHS tapes laying around, including some that are recordings of TV broadcasts like nightly news from many years ago, etc. These could be interesting signal sources to analyze, if I could find a USB composite video input card that I could connect a video to, if said USB composite video input devices (and corresponding drivers) in fact were allowed to send the WHOLE FRAME (including the extra lines, for a total of 525 lines) to be saved as an AVI file for later viewing. Anybody know if such USB devices exist, or even if PCI or PCIe devices exist that have this capability (and are not limited to recording only the normal 480 lines)? What website sells such devices (if such devices exist)? This could be a potentially very interesting thing to look into, with the right equipment.
    You are correct that the VBI could be used for other things beyond closed captions and macrovision. U.S. analog TV signals included V-Chip content rating, and the CGMSA copy protection flag in the VBI. My cable TV provider did use the VBI for the channel name, the name of the program being broadcast as well as the date and time of the broadcast, but since I never recorded OTA analog TV, I don't know if OTA broadcasts typically included it too. Years ago I could read such information mixed with the closed captions when I played DVDs from my DVD recorder using an old version of PowerDVD, so it must be adjacent to Line 21 closed captions and use the same type of encoding.
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    Interesting material, certainly!

    But I can't help being glad that those analog days are almost completely behind us.

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    Originally Posted by lordsmurf View Post
    Easy explanation: Analog "lines" has nothing to do with digital video resolution.
    With regard to "TV lines" (horizontal) you could say this, but the thread title was asking about the discrete vertical scanlines. The vertical digital resolution is absolutely related to the standard number of active scanlines: they are identical except for rounding down the NTSC number to be divisible by 16, and filling in the half-lines for PAL.
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  20. Originally Posted by vaporeon800 View Post
    Originally Posted by lordsmurf View Post
    Easy explanation: Analog "lines" has nothing to do with digital video resolution.
    With regard to "TV lines" (horizontal) you could say this, but the thread title was asking about the discrete vertical scanlines. The vertical digital resolution is absolutely related to the standard number of active scanlines: they are identical except for rounding down the NTSC number to be divisible by 16, and filling in the half-lines for PAL.
    True - vertical lines or rather "real" lines are discrete and valid for both systems (analog and digital), horizontal "lines" are related to particular picture http://www.ntsc-tv.com/ntsc-index-04.htm Name:  line-pairs_11.gif
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  21. So, this leaves me wondering, some things. Does 486 lines means 480 image lines + 6 lines that can be used for storing digital metadata? Or is it 486 image lines (but computers tend to ignore 6 of those lines), leaving only the blanking region able to hold digital data? And when 486 lines are shown on a real TV, are those 6 extra lines what is normally called the "overscan region"? Or does compensating for overscan actually involve cutting off more than 6 lines, or maybe fewer than 6 lines?
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    Originally Posted by Videogamer555 View Post
    Does 486 lines means 480 image lines + 6 lines that can be used for storing digital metadata? Or is it 486 image lines (but computers tend to ignore 6 of those lines), leaving only the blanking region able to hold digital data?
    I feel like this was covered towards the end of your more recent thread.

    And when 486 lines are shown on a real TV, are those 6 extra lines what is normally called the "overscan region"? Or does compensating for overscan actually involve cutting off more than 6 lines, or maybe fewer than 6 lines?
    Overscan cuts off "some" amount vertically and horizontally. It's unrelated to specific "extra" lines at the top of the image.

    https://en.wikipedia.org/wiki/Overscan#Overscan_amounts
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    i'd only add that an analog ntsc frame is only 262.5 lines. analog tv was scanned vertically twice to make a complete image. that's why pal "flickers" at 25htz and ntsc at 29.97htz doesn't to the human eye.
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    262-1/2 lines is not a frame. It's a field. PAL is also interlaced, so I'm not sure what you're getting at. Phosphor persistence operates in both cases and the difference in flicker is very small. (I'm talking about pure video, not telecine or other conversions.)
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  25. I agree. The difference in flicker is small. And they both flicker obviously with some material.
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    I think aedipuss is talking about the perception of flicker to users, but this also really touches on "what you're used to". SD NTSC users notice the flicker of SD PAL rates because it's slower...until they get used to it. SD PAL users notice the lesser resolution of SD NTSC...until they get used to it. PAL users have no trouble with NTSC rates, because it's already higher. Similarly, NTSC users have no trouble with PAL resolutions, because it's already inherently better. Potato, Potahto...

    Scott
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    yes. thank you cornucopia. and there were differences in phosphors. tvs with long persistence phosphors smeared fast movement, short persistence phosphors flickered more. field/frames don't have as much meaning in old analog broadcasting. tv pictures were updated one line at a time starting at the top of the screen moving to the bottom and repeating for the in-between lines of the odd/even raster pattern. it never stopped as a complete field or frame.
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  28. Flicker perception depend from many thing - personally never suffered to much from PAL field/frame flicker - key to this is proper lighting conditions (avoid watching TV in dark room, provide some ambient light behind TV etc)...

    Originally Posted by Videogamer555 View Post
    So, this leaves me wondering, some things. Does 486 lines means 480 image lines + 6 lines that can be used for storing digital metadata? Or is it 486 image lines (but computers tend to ignore 6 of those lines), leaving only the blanking region able to hold digital data? And when 486 lines are shown on a real TV, are those 6 extra lines what is normally called the "overscan region"? Or does compensating for overscan actually involve cutting off more than 6 lines, or maybe fewer than 6 lines?
    Usually those lines are VBI - if they can or not be used for VBI - don't know - seem that VBI is less standardized in US than in Europe also seem that demand for data transmitted within TV signal was lower in US than in Europe.

    480 selection was clear - dividable by 16 so MPEG-2 expectation meet.
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