Why are there so many misconceptions with regards to time code? With all of these numbers floating around, many people tend to be totaly confused. Well, it's simple... with a little explanation of course..
We get about three calls a week regarding mis-information about time code. Using the wrong time code can cause serious sync problems. Unfortunately, many people in the industry don't completely understand the differences in time code frame rates. If you walk into most video post houses, they might tell you that they record 30 fps time code on their videotapes. WRONG!! They say 30, but it is actually 29.97.
For Clarification Purposes: We are talking about synchronous film and video projects done here in the United States, NTSC Standards.
29.97 is Drop Frame .... and 30 is non drop.
WRONG
The standard SMPTE time code found on videotapes is 29.97 fps. This is the rate that video is broadcast in the United States. So it is simple to remember that when dealing with videotape, we are always talking about 29.97 fps, NOT 30.
There is a difference between 29.97 and 30 fps. That difference amounts to .1%. (This .1% will be coming up a lot in this discussion, so don't forget that number.) The difference between 29.97 and 30, in film frames amounts to 2 frames (1.8 to be exact) every minute. A tape with 29.97fps time code, will run .1% faster if locked to a reference of 30fps time code.
The ability to play a tape back at either .1% up or down allows us to vary the programs speed according to the same difference created when transfering film to NTSC videotape.
When 24fps film is telecine transfered to videotape, the film must be played back .1% slower in order to create a video with 29.97fps (the rate of video). While the film is being slowed down, the telecine is creating a precise pattern of frames onto the video signal. The pattern is know as the 3:2 pulldown. The first film frame is copied three times onto three fields of the video signal. Then the next frame of film is copied to the next 2 fields of the video signal. This 3:2 pattern continues... If the film was not slowed down this .1% then we would end up with a video that contained 30fps. (Color video cannot be broadcast at 30fps). We slow down the film in order to end up with 29.97fps.
The bottom line, don't confuse the two rates, they are different and must be used properly. Many video facilities will tell you that they will record 30 fps time code on your tape... when in reality, they are just too lazy to say 29.97.
MISCONCEPTION #2
You lose frames of footage when switching between DF and NDF. WRONG.
Program length doesn't change when using Drop Frame or Non Drop Frame.
Drop frame time code drops two frames every minute except every tenth minute. No physical film or video frames are dropped, only the time code frame numbers, (:00 and :01) are dropped. (A program with Non Drop Frame Code is the same physical length as the same program with Drop Frame Code.) The difference is as follows:
IN DROP FRAME
01:12:59.29 will change to
01:13:00.02 - skipping the 00 and 01 frame numbers. On the tenth minute, no frame numbers are dropped so that:
01:19:59.29 will change to
01:20:00.00
IN NON DROP FRAME
01:12:59:29 will change to
01:13:00:00
Drop frame is used in order to closely time the length of your program by the time code read out. If you started your program at 01:00:00:00 (using DF) and played into the show 12 minutes, your time code will read very close to 01:12:00:00. Drop frame is usually used on broadcast master tapes. When in doubt, for editing and offline purposes, us NON DROP FRAME... it's easier to work with. You can master to a Drop Frame tape later.
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