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NTSC PAL reality

Discussion in 'Other video questions' started by jasperbox, Jun 5, 2013.

  1. jasperbox

    jasperbox Member

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    PAL is slightly faster than NTSC. Which one is "reality" speed?
     
  2. attar

    attar Senior member

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    NTSC and PAL being TV standards - not movie standards.
    Reality once was that all movies everywhere were 'filmed' on celluloid at 24fps.
    Inside the cinema building, it was projected at that speed everywhere.

    When TV came along, in NTSC regions, the video was pulled down to 29.97fps for retail DVD's - no change in the audio.
    For PAL, a speed up from 24 to 25fps resulted in the audio pitched higher - which hardly anyone noticed.

    Today, where celluloid is dying out, a PAL movie can be 'filmed' at 25fps and slowed down for NTSC (slowed to 23.976 then pulled down to 29.97).
     
  3. jasperbox

    jasperbox Member

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    I don't understand.

    a film is shot at 24fps so the "reality speed" of real life captured in that movie will be 24fps. If you speed it up to 28fps then peeople would be moving and talking faster than reality. If you slowed it down to 20fps they would be slower than reality.

    so then PAL would be a little faster, and NTSC even more faster? That doesnt make sense.
     
  4. attar

    attar Senior member

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    NTSC isn't faster;it's because of the so called pulldown effect.
    You are playing the video faster (as you would expect) - but you interpolate repeated video frames (or your playback device does because it sees the instruction flags in the video stream).
    The upshot is that you have more frames to display - but you play them at a faster rate, thus the running time remains the same.
    And the reason you must do so in North America is because TV demands it.

    http://en.wikipedia.org/wiki/3:2_pulldown#23pulldown

    If you ever go through the exercise of converting a 25fps avi video to NTSC DVD format, you first convert it to 25fps mpeg2 format then apply pulldown from 25 to 29.97 using a program called DGPulldown.
    The running time of the original AVI isn't changed thus the audio stays in pitch.
     
  5. attar

    attar Senior member

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    Here's an example.
    Note the first three images are different (his mouth changes).
    The last two are created from parts of the preceeding frames.
    The lines around the face indicate that the frames were made from slightly different times.
    This is how they create extra frames to keep the original running time the same when played back at a faster rate on NTSC TV screens.



    [​IMG]
     
  6. jasperbox

    jasperbox Member

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    O I C

    thx for that stretching explanation.

    ...so can one say NTSC is always reality speed? and since PAL is higher pitched, then PAL is always faster than reality speed?
     
  7. attar

    attar Senior member

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    You could only state that confidently in the days when all movies were created using celluloid (they were all filmed at 24 FPS):you can't assert it in the digital age.
    And it's helpful to remember that the movie being played in the cinema is the same movie in North America or Europe - it's only for TV purposes that the changes are made.

    The glaring example is when the boys are going out of the trenches in the Great War;they actually didn't walk funny back then - it was filmed at a slower frame rate that looked perfectly natural when projected in the movie house in 1918;it's showing it on TV that makes it look odd.
     
  8. jasperbox

    jasperbox Member

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    An NTSC video playing on an NTSC TV is exactly the same speed as a PAL video playing on a PAL TV?

    Does that mean an NTSC video playing on a PAL TV is slightly slower?
     
  9. attar

    attar Senior member

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    It would unless steps were take - I don't know how the process works when it comes to video sources (as opposed to film).
    For broadcasting by the likes of the BBC? - I assume that frames are removed from the source then played back at the lower frame rate keeping the running time the same.
    Your PAL DVD playback device can take NTSC video (a made for TV movie that is 29.97) and play it back at 25 fps ok.
     

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