What is drop vs non-drop?

Discussion in 'Amateur Video Production' started by Doc, Nov 29, 2004.

  1. Doc

    Doc Guest

    What's the difference between drop frame vs non-drop, two options I see in
    preferences regarding files.

    Doc, Nov 29, 2004
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  2. Doc

    Funprice Guest

    It has to do with the 29.97 frames per second timebase of NTSC and a
    chosen frame rate of 30 in your editing program. So when editing NTSC
    there is a slight difference between the stated duration of the
    program and its actual duration. When you use 'drop-frame timecode'
    the editing program renumbers certain frame numbers to keep the stated
    duration of the program exact (time accurate). So 'drop-frame
    timecode' drops frame numbers not frames as you would think.
    Funprice, Nov 29, 2004
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  3. Doc

    david.mccall Guest

    That's right, drop-frame is used to correct for a time discrepancy
    between the actual video rate and timecode.

    Color video is delivered at a rate 29.97... frames per second
    instead of the 30 frames per second use in the original black
    and white standard. 30 was convent because of the 60 cycle
    power being used in the US. However, when color came along,
    there were many timing issues that had to be more precise
    than anything required by black and white TV.

    There are several specific references that are needed to decode
    a color TV signal vertical frame rate, horizontal frame rate, field
    order, color subcarrier and color burst phase and placement,
    among other little details. A common frequency had to be chosen
    that would yield enough pulses in the right place to create these
    all of these references in an analog world. I think that frequency
    worked out to ~14.32 mhz. It required a slight compromise in the
    frame rate to get everything to fall into place. That is how we
    wound up with 29.97 instead of 30.

    Since 29.97 is slower than 30, it takes more than an hour to
    get to a time code of 1:00:00:00. To make up for this, some
    frame numbers get skipped over to make the count come out
    to the right number to match the actual length of the program.

    So, only frame numbers are skipped, and all of the video are
    left in place. Most video is done using drop-frame time-code
    but many people find the missing numbers confusing, and
    prefer to work in non-drop frame. If you are doing a short
    project, or any project where the time discrepancy wouldn't
    be an issue, then you can use which ever you prefer.

    david.mccall, Nov 29, 2004
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