29.97, 30fps and digital video (question)

Discussion in 'Amateur Video Production' started by genericaudioperson, Jul 22, 2005.

  1. hello,


    in video tape days, there was 29.97, 30 frames per second, "non-drop",
    and all this frame stuff.

    if you are in a modern, completely digital system (miniDV
    camcorder>>firewire>>computer>>DVD burn), are "frames" still a
    necessary part of it all?
     
    genericaudioperson, Jul 22, 2005
    #1
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  2. Digital video (DV) is still 29.97fps (drop frame timecode). You would not
    want to use "non-drop frame timecode" as you will then see dropped frames
    and come back here in a panic asking, "why am I getting dropped frames?"

    Even progressive video has frames. How do you suppose motion can be created
    without the use of frames?
     
    Innocent Bystander, Jul 22, 2005
    #2
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  3. genericaudioperson wrote ...
    The North American video standard (the black & white version,
    now called "RS-170") started out at 30 Frames Per Second.
    When they overlayed color on top of the existing standard,
    it became "NTSC" (National Television Standards Committee)
    They had to change the frame rate by 0.01% to 29.97 FPS to
    fit the color information into the same 6MHz-wide television
    channel.

    In order to be able to show video on conventional TV sets,
    NTSC must maintain the same 29.97 FPS frame-rate,
    regardless of whether the signal is from a live camera,
    analog tape, digital tape, or from a computer file.

    "Drop-frame" refers to the practice of skipping a frame
    NUMBER (NOT an actual frame of video) every few
    minutes in order to keep the 29.97/sec frames in sync
    with the wall-clock "real" time.
     
    Richard Crowley, Jul 22, 2005
    #3
  4. so if i'm going Mini DV>>firewire>>computer>>DVD burn, then i should be
    working in "29.97 drop frame". did i get that correct?
     
    genericaudioperson, Jul 23, 2005
    #4
  5. genericaudioperson wrote ...
    Yes. Although "Drop-frame" doesn't really matter.
     
    Richard Crowley, Jul 23, 2005
    #5
  6. You wouldn't get dropped frames - the motion would still be smooth.
    Drop frame timecode simply drops certain frame *numbers* in order to
    keep it (nearly) in sync with the passing of real time.

    Now, if someone used drop frame time code without understanding it, and
    looked at the frame numbers of successive frames, they might *think*
    that some frames had been dropped because of the gap in the sequence.
    But that's not the same as frames that were actually dropped.

    Dave
     
    Dave Martindale, Jul 24, 2005
    #6
  7. Not quite. The colour information fits into the existing bandwidth
    without the frame rate change. The reason for the change is that they
    wanted the frequency difference between the colour subcarrier and the
    *sound* carrier to be an odd multiple of the line frequency, to minimize
    the visibility of sound leaking into the picture in a receiver that
    processed both together. They had the choice of moving the sound
    carrier up slightly, the frame rate down slightly, or doing nothing at
    all.

    I think most TV transmitters at the time used separate sound
    transmitters, so moving the sound frequency would mean any TV station
    would have to retune its sound transmitter when switching to colour.
    Instead of requiring this, the NTSC committee decided to change the
    frame rate by 0.1% (not 0.01%).

    At the time, there was no time code to worry about.

    Dave
     
    Dave Martindale, Jul 24, 2005
    #7
  8. "Dave Martindale" wrote ...
    Yeah, I was trying to give a relatively simple answer to a
    simple question. Seems doubtful that the OP really cares
    about the finer points of slotting the color subcarrier power
    harmonics, or the relative offset of the sound carrier, etc.
     
    Richard Crowley, Jul 24, 2005
    #8
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