[This article was first published in the April, 2008, issue of
Larry's Final Cut Pro Newsletter. Click here to subscribe.]

Robert Hurt writes:

I produce an HD vodcast for NASA that involves a fair amount of pan and scan movies generated from images. Since these often exceed Motions 4k image resolution I typically will render these in After Effects.

My problem is this. We produce at 720p24 to be AppleTV compatible, and as we use an HVX200 in 720p24N format I've standardized on a FCP sequence format of full 720x1280 (to preserve full resolution of our animations) at 23.98 fps (to match the HVX footage).

The problem arises when I try to export Quicktime format movies from AE (version 6.5 still) at 1280x720 at 23.98 fps. By all observable indicators this is an identical frame rate to my FCP and Motion timelines, but when I import it there seems to be significant stuttering.

In FCP it plays back nice on-screen, but anytime there is a transition the rendered result stutters. If I force the entire export to recompress then all of the animation stutters, including the transitions.

If I put it into Motion, the stuttering is immediately obvious, as stepping through frame by frame yields irregular results.

The only workaround I've found so far is to export as a frame sequence, import into Quicktime Pro at 23.98, export into ProRes .mov, then import that. This gets kind of kludgy with lots of clips.

Is there a known frame rate disconnect between AE and FCP, or perhaps some magic settings that would allow for a more direct export to .mov workflow?

Larry replies: My suspicion is that the frame rates between FCP and AE don't match. Take a closer look there.

Robert then wrote back:

The frame rate is INDEED the trick, and FCP appears to be VERY picky about its exact value.

If I export from AE a ProRes .mov with the frame rate set EXACTLY to 23.976 then FCP ingests it and renders it fine.

If the AE export is set to 23.98 (which I had been doing) then FCP ingests it, displays it, but gags on the render because it appears to not truly accept it and apparently conforms its sequence to be 23.976 instead.

The trick of it is that the info panel in QuickTime shows both movies to be 23.98 fps, so there's no obvious way that I can find to tell the difference between a "good" 23.976 and a "bad" 23.98.

You'd hardly expect that a 0.004 fps variation should cause FCP and/or QuickTime to muck up roughly every third frame on re-render, but apparently it DOES!

Who knew?

Larry replies: Robert, thanks for sending us the solution. I'm delighted to share it with others.

UPDATE - April 8, 2008

Tom Wolsky sent in the following:

FCP calls its frame rate 23.98 for shorthand, but the real frame rate is 23.976, which rounds-up to 23.98. FCP only lets you make sequences in specific, exact frame rates, it's 23.98 is really 23.976. AE on the other hand will make any crazy frame rate you want, 22.4, 28.3, anything. You asked for 23.98, you got 23.98. As Robert found out, you have to ask for the real "24p" frame rate, which is 23.976.

Larry replies: Thanks, Tom.

Larry Jordan is a post-production consultant and an Apple-Certified Trainer in Digital Media with over 25 years experience as producer, director and editor with network, local and corporate credits. Based in Los Angeles, he's a member of both the Directors Guild of America and the Producers Guild of America.

The information in this article is believed to be accurate at the time of publication. However, the author assumes no liability in case things go wrong. Please use your best judgment in applying these suggestions.

The opinions expressed in this article are solely those of the author. This newsletter has not been reviewed or sanctioned by Apple or any other third party. All trademarks are the property of their respective owners and are mentioned here for editorial purposes only.

Links to my website home page or this article are welcome and don't require prior permission.