Reconciling Video Frame Rates Between After Effects and Final Cut Pro
[ This article was first published in the April, 2008, issue of
Larry's Final Cut Pro Newsletter. Click here to subscribe.
Updated - Jan., 2009, and Jan. 2011. ]
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 720×1280 (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 1280×720 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!
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.
UPDATE – January 2009
Nate Adams sent in the following:
I read your article on reconciling frame rates. I, too, have experienced this recently on a project that was receiving graphics rendered out of After Effects at 1080/23.98 (not 23.976) 8-bit and dropped into an FCP timeline. Now I want to kick myself for not trying to render things out of After Effects at 23.976. As long as the FCP render engine didn’t touch the footage it was OK, but as soon as something was rendered in FCP it stuttered.
We went through it frame by frame and noticed that frames were actually getting left out and others doubled, and with no specific cadence. STILL FRAME>REPEATED STILL FRAME>MOVING FRAME>STILL FRAME>…and so on. Unfortunately we were renting two bays at the time including a 2k Da Vinci theater for bazillions of dollars a second, so we didn’t really have time to fuss around. We ended up buying and using Automatic Duck to bring the sequence out of FCP without any effects, into After Effects. There we’d add the dissolve or motion effect, render out of AE, and drop it back into FCP. Strangely enough, FCP was the only application that couldn’t interpret 23.98 material properly as 23.976. Scratch, Motion, After Effects, were all fine.
Larry replies: Thanks, Nate, for sending this in.
UPDATED — JAN. 29, 2011
Michael Price, with Starz Entertainment, sent this in:
We just discovered this problem and spent some time troubleshooting this issue before coming up with a workable solution.
If Final Cut Pro is installed, there is also an application called Cinema Tools that will allow you to batch conform multiple files to the proper frame rate. For instance, if you discovered after the fact that you rendered 20 clips in After Effects at the incorrect frame rate of 23.98, you can use Cinema Tools to conform them all in seconds to the correct “23.98″ which is actually 23.976. It does this by changing the playback frame rate in the header, not by changing any frame or pixel data.
Be careful, because if you select a file in a folder, it will automatically conform every file in the folder, not just the selected file.
Larry replies: Thanks, appreciate the update!