QUESTION: I have tried converting the movie but have I still get the frame skip every second...i cant seem to get the imagery converted to 24 fps correctly.

I've used AE to covert feature films shot at 25 fps to 24 with no problems.

History: back in the days before inexpensive 24P cameras, independent filmmakers would shoot in PAL DV, and then convert that 25 to 24 fps, and this would result in a *very* film-like look. In fact, the very first version of "Magic Bullet" was targeted at this specific task.

The principal issue is that there is a 4% speed change in the footage. This 4% is a common issue in the interchange of media from NTSC and PAL markets. In general, the preferred conversion method from NTSC to PAL or vice versa uses 24 FPS as the intermediate stage. In NTSC to PAL, fields are dropped to bring the interlaced 29.97 footage down to 23.976i. Then this would be sped up 4.1% to 25 fps. PAL to NTSC used the reverse of this path.

In the case of music content, it might become necessary to use a pitch shifter (such as Lexicon PrimeTime) to adjust the pitch due to the 4% change.

Your case:

So, it appears what you have 25 fps HD footage? The conversion is simple: In After Effects you can:

1) Bring in the footage and interpret it as 23.976 (or 24.00 depending on your delivery requirement). However, in this method you will need to convert the sound in a separate application, such as ProTools (this is preferable to After Effects, as ProTools has substantially better algorythyms for sample rate conversion).

1b) In this method, bring the sound into ProTools and sample rate convert it. If your sound is at 48K at 25 fps and you are going to 24 fps, then interpret the sound as 46080 Hz, and convert to 48000. If you are going to 23.976, then interpret the sound as 46033.966034 Hz. See the attached PDF document for more conversion numbers.


2) Or, bring the footage in via AE, interpret it at its present rate of 25, and then use time remapping to convert it to 24 or 23.976.

Andy's List of Pulldown Numbers

In relation to pulldown, the true ratio is 1001/1000. This results in periodic decimals (infinitely repeating) for many of the conversion numbers.

For instance, the commonly used 23.976 is actually rounded from the periodic repeating decimal 23.976023976023976023976...

In practical reality, some software applications round off at three or four decimal places, though this is incorrect and will result in drift. Some will report the rounded number to the user, but will internally use the correct number at least out the the limits of double precision variables.

There are 172800 frames in a two hour movie - rounding at 4 decimal places will produce a drift of more than one frame over that period.

NOTE: 0.1% is only correct when pulling UP. When pulling DOWN, it is actually 0.0999000999000999000....% To understand this math, consider that if you take a value of 100 and increase it to 150, you have increased it by 50%. If you then take 150 and reduce it back to 100, you have now decreased it by 33.33333 % (this is a common concept for investors, that a 33% loss requires a 50% gain just to break even).

The "true rate" of 23.976 is

23.9760239760239760239760239760239760... (infinitely repeating)

When calculated on a calculator with 25 digits precision, the rate change from 25 to 23.976023976... is:

To keep a two hour film in sync within a frame, you need a minimum of 8 digits of precision (that is, 6 digits after the decimal point or 23.976023)

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