GH3 GH4 Cinema 4K is 24fps, not 23.976fps?

Jaime Valles

Jaime Valles

Veteran
Howdy.

I'm curious about the spec sheet for the GH4, which indicates that shooting in Cinema 4K (4,096 x 2,160) will be at 24.00 frames per second, and not the traditional 23.976 frames per second of most digital cameras. Is this going to cause any type of headache with our NLE software, or with audio sync during post? Or is it a non-issue?

I know film is shot at pure 24fps, so I'm assuming most NLEs will be able to handle it just fine. Though I wonder what happens if we mix 24fps with 23.976fps footage in the same timeline. I'm not particularly worried, just curious.

Thanks!
 
If that's true, I would imagine it would cause issues with audio drift on external recorders. At least that's what I thought happens in theory.
 
Using a true 24 fps patch on the GH2, I've not noticed any unusual drift with audio recorders, meaning it's the same drift at 24 that it is at 23.976. With the zoom H4n I see less than one frame drift over 45 minutes.

However, 24 fps and 23.976 may not match very well. While I've not added both to the same sequence, I did notice stutters from my 24 fps media when added to a 23.976 sequence, which shows that there is a difference.

Since I do notice an admittedly subjective improvement in 24 over 23.976, since BD can handle 24 exact, and since DVD shows nothing unusual when exporting 24 exact at the required 23.976, I think recording in both Cinema 4K and even HD at true 24 fps is a very welcome addition to the GH4.
 
Audio shouldn't be a problem in the reality of editing. Maybe very long clips but then who shoots very long clips in cinema 24p...?

Like stated above framerate is more of an issue. 23.97 and 24 is not the same as should be treated as such.
 
I recall from an Avid editing class that if you shot in 23.976 you needed to slow down the audio by like .1% or something to that effect, or else there would be drifting. I don't know if other editing software automatically address the issue. A quick Google search indicates that it is an issue with other editing software as well: https://www.google.com/#q=24p+23.976+audio+drift
 
I forgot to include a critical piece of information: this was for double-system sound only. Obviously in single-system you should not need to worry about the audio drifting. Also, like someone said above, it should only be noticeable in really long takes. This would probably be more of a concern for documentary films.
 
Shenan said:
I recall from an Avid editing class that if you shot in 23.976 you needed to slow down the audio by like .1% or something to that effect
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I don't believe you read that correctly. There should be no drift using 24 fps instead of 23.976. The fact that there is drift is not due to the frame rate of the image, but to the inability of audio records to record at exact timings. I don't know why audio devices have this problem when in my experience, video devices (even across manufacturers) can record with exact timings such that even 1 hour long takes will remain in sync for the full recording. But, for whatever reason, audio devices just seem to have issues recording with precise timing and may need adjustment to match the video in post. I find that this drift varies by device, and will stay pretty consistent for that device. Meaning a .04% adjustment needed to maintain audio sync with the image will apply regardless of what frame rate (or even which camera) was used to record that image.
 
Jim, I think you're correct that there should be no issue, as long as the project is edited at the same exact frame rate as it was shot on. I believe the case they were covering was projects shot on film (exact 24fps) being edited on 23.976 timelines (or it might even have been film telecined with 2/3 pulldown into 59.97i video). A scenario like that slowed down the video playback just slightly, which required an equivalent slow down of a double-system sound audio track. Thanks for jogging my memory - I should have been more precise from the beginning, and realized that that kind of situation would not have been applicable in most cases nowadays.
 
There is only a 0.1% difference in speed between 24fps and 23.976. That's only 1 frame in every 1000, or 41.6 seconds. If I was needing to mix both on the same timeline, I'd reinterpret the odd footage to match the main one. Yes, the action will move 0.1% faster or slower, but who will notice?

Jim Simon said:
I don't know why audio devices have this problem when in my experience, video devices (even across manufacturers) can record with exact timings such that even 1 hour long takes will remain in sync for the full recording.
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The oscillators that control all audio and video equipment are not accurate enough to retain sync for long periods. The reason video always lines up is that the signals are re-synced at every frame. This can also be done with high-end audio gear that has SMPTE or MIDI Time Code.
 
Video (and audio) devices stay in sync because they're fed a reference signal, commonly known as black and burst, or station syncs. This technology is as old as the hills for post houses everywhere, and guarantees no drift. Just record your sound at the same frame rate as your camera, and you're golden.
 
This is only an issue if you record 24p on one camera and 23.976 on another camera. Then you may get drift. 24p in a 24p timeline will be just fine. An external audio recorder doesn't really care what framerate you shot in unless it can sync timecode which I will assume most of us are not doing. Audio from a free run external recorder will be fine as long as you edit 24p in a 24p timeline or sequence. Put 24p in a 23.976 timeline then yes of course the external audio will drift over time. Same thing if you put 25p or 30p or 60p in a 23.976 timeline. As long as the sequence matches the source framerate you are fine.

17x9 4k really has little place in the broadcasting world and really is strictly for cinema distribution which would want 24p and not 23.976. If you plan on broadcasting or distributing to DVD/Blu-ray in the NTSC market you are much better off shooting 3840x2160 which is 16x9 and can use 23.976.
 
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