Archived from groups: rec.video.desktop (
More info?)
"Funprice" <jhbusscherNOSPAMWHATSOEVER@freemail.nl> wrote in message
news:d88mq01q5pmaprn3gkndl14i5u3f2qerrq@4ax.com...
> On Mon, 29 Nov 2004 09:34:07 GMT, "Doc"
> <docsavage20@REMOVEhotmail.com> wrote:
>
>>What's the difference between drop frame vs non-drop, two options I see in
>>preferences regarding files.
>
> 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.
>
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
Facebook
Twitter
Instagram