making 23.976fps into 24fps


johnmeyer wrote on 12/3/2013, 11:40 AM
But, it is 24 actual frames, why not just call it as it is, skip those annoying hundredeths of seconds?Again, there is a lot of confusion here that is going to lead to bad decisions on what to do. The odd numbers (29.97, 23.976, etc.) happen because the speed of playback is being expressed in terms of how many frames are projected in one second. If you project film in a variable speed film projector, and turn the speed knob to increase or decrease the speed, there is never a fractional frame shown because the mechanics would never allow that. However, the speed, when measured as how many frames are actually shown each second, is never going to be an exact integer like 16, 18, 24, 30, etc. because the speed control is an analog control and not locked to an atomic clock.

If you feel more comfortable expressing these odd speeds as integers, then you can say that 24,000 frames are shown in 1001 seconds. If you divide 24,000 by 1001, then you will get 23.976 frames per second.

So the point of this post is to make sure that everyone understands that frame rates that are not perfect integers (i.e., nothing but zeros to the right of the decimal point) have nothing to do with showing "fractional frames."

My recommendation: download Mediainfo and then drop some video from your camera onto Mediainfo. Then, note the frame rate and, in Vegas, match everything (project and render frame rate) to this number and get on with life. I am 100% certain that the theater projector will be able to play the resulting file.
robwood wrote on 12/3/2013, 11:44 AM
"I doubt the Digital Cinema Package creation consisting of TIFFs or JPEG2000 would be interested in .976 of a frame."

23.976 just means the video plays s-l-i-g-h-t-l-y slower than 24.

it's like driving at 23.976 rather than 24... you still do all the driving; it'll just take a few thousandth's of a second longer to get there.

edit- nm... in the time it took me to write this you got a half-dozen better answers.
larry-peter wrote on 12/3/2013, 12:21 PM
The main issue with digital cinema delivery of non-integer frame rates is the audio, so by using either the method I suggested in an earlier post, or Bob's method of noting absolute frames and matching that in a 24fps timeline and re-rendering the audio track will give you what you need for cinema. The DC systems always clock to 48k or 96k, and the audio stream is separate from video in the DCP, so give them the proper length audio for a 24fps playback and their system will spit out the frames at 24 per second.
farss wrote on 12/3/2013, 12:54 PM
Jphnmeyer said: [I]"However, the speed, when measured as how many frames are actually shown each second, is never going to be an exact integer like 16, 18, 24, 30, etc. because the speed control is an analog control and not locked to an atomic clock. "[/I]

Pretty well everything in broadcast and film today is locked to UTC via GPS. Modern film cameras use crystal oscillators, in fact the development of such motors was a huge leap forward in the film world. Without it the movie Woodstock couldn't have been shot.

As far as I could find out film projectors in cinemas are just locked to mains frequency...near enough I guess :)

None of my cameras have the ability to lock to external timecode and I'd guess the same applies to the majority of people here. Technically speaking then my camera can shoot 25.000 fps but not 25.0000000 fps. That is an issue when it comes to two cameras shooting the same things, the accumulated error will eventually mean the video and sound recorded by them will become noticeably out of sync.

For this discussion that doesn't matter, two thing that do matter are:

The video is flagged as intended to play out at 25.0000000 fps and there will be exactly 48,0000 audio samples for each 25 frames because both the video and audio clocks are derived from the same source i.e. any small error will affect both proportionally.


wwjd wrote on 12/3/2013, 1:06 PM
K, I got it now: I'm saying number of frames, but really it is playback SPEED. Sorry, took me a bit to really sink in. :) in the end, I still plan to aim at only 24p and see how well that works for me.

last night, I rendered a 24p version of my latest epic to use to dice up for a teaser trailer... well, making a 24p teaser out of clips cut from the 24p render did some weird things: instead of snapping together, SOME were overlapping and adding crossfades, not ALL, just a couple. It was a rushed work so I didn't have time to really hunt down why, but wonder if it is related to 24p somehow since I don't recall seeing it happen?
Not seeking solutions, just mentioning since it never happened messing with normal clips, just the 24p one. Probably nothing. Maybe I was halucinating too
larry-peter wrote on 12/3/2013, 1:12 PM
Source frames not matching timeline frame boundaries is generally the cause of this - as was mentioned a few times in this thread. Everyone deserves whatever learning experience they choose, but I still scratch my head at why you want to edit 23.976 in a 24fps timeline. You can easily conform a 23.976 master to 24 using the tips in this thread, and if you eventually get a true 24p camera, this strenuous exercise you're undertaking will no longer be applicable - because then you'll be doing what everyone has recommended - editing with the same project properties as your source footage.
wwjd wrote on 12/3/2013, 2:07 PM
" why you want to edit 23.976 in a 24fps timeline "

... because it is there. :)
johnmeyer wrote on 12/3/2013, 2:08 PM
Pretty well everything in broadcast and film today is locked to UTC via GPS.Bob,

I was simply trying to drive home what happens with a simply variable speed consumer movie film projector which, except for a few with synchronous motors, have nothing more sophisticated controlling the film speed than a rheostat. I wasn't trying to address any concerns about the theater playback device, but was simply addressing the fuzzy thinking that was leading to the idea that non-integer frame rates were somehow going to lead to one frame being shown for a really short period of time, or perhaps only part of the physical frame was going to be shown.

I am well aware that cinema projectors (and professional cameras) are (or at least were) all designed to lock to some sort of timebase which can be driven by a crystal or by a signal from the NBS (in this country, the National Bureau of Standards broadcasts time signals over the air and via the Internet).