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Working with 60p in Apple Final Cut Pro

Dec 7, 2010 12:00 PM, By Jan Ozer

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Adding 60p footage to a 29.97i sequence

Intuitively, when you convert 60p to 29.97i—say, for producing a DVD—you want to convert the 60 original frames into 60 fields, with each field containing subsampled information from a discrete frame. That way, when you play back the video, you still get 60 discrete impressions per second, preserving the motion, though an interlaced field obviously contains less information than a complete progressive frame.

The first problem I encountered in Final Cut Pro was when I added a 60p file to a 29.97i sequence that contained SD 29.97i content destined for a DVD. Specifically, the 60p video didn't look smooth, and when I analyzed the file that I produced (with the timecode), I noticed that Final Cut Pro didn't convert the frames into fields; rather, it seemed to convert the 60p sequence into 30p, then create interlaced fields from the 30 frames. This eliminated half of the original frames and introduced a slight stuttering into the video, which was noticeable particularly in the pans in the sequence.

I Googled around and found this in the Creative COW boards from poster Shane Ross: "You want to convert progressive to interlaced? Because just dropping the footage onto a FCP timeline won't do that. All it will do is take the 60 frames per second, and remove every other frame to make it 30fps."

Ross recommended converting from 60p to 29.97i in Adobe After Effects, stating that "After Effects is a compositing application designed to do what you want in that case." However, Ross didn't detail how to effectuate this conversion.

Desperately seeking to avoid attempting to recreate what's already been created, I Googled a bit more, and found a well-documented procedure in the Creative COW Magazine in an article entitled "Interlacing Progressive Footage" by Marco Solorio.

Solorio pointed out that you could actually convert from 60p to 29.97i in Final Cut Pro or Compressor as well, though you can't do it from a 29.97 sequence in Final Cut Pro. Specifically, in Final Cut Pro, if you edit your 60p footage on a 60p sequence, then render to 29.97i in Compressor, you get the proper result— that is, 60 fields, each containing discrete information from an original 60p frame. Or, you can just input the 60p footage directly into Compressor, render out the 29.97i footage, then input that into your 29.97i timeline.

Figure 2. Setting up the composition in After Effects.

Figure 2. Setting up the composition in After Effects.

I successfully used both techniques, rendering out to a 720x480 16:9 interlaced ProRes 422 (HQ) file that integrated perfectly into my 29.97i ProRes 422 HQ sequence, with no red line atop the timeline and no re-rendering. I also successfully produced the same result in After Effects, following this basic procedure documented in Solorio's article.

1. Create a 29.97i composition in After Effects and drag the 60p footage into it. I created the composition at my target resolution, though other sources that I found recommended scaling from 720p to SD in Final Cut Pro, then converting from progressive to interlaced in After Effects. Whatever you do, don't convert from 720p to 720 interlaced, and then scale down to 720x480, since you should get a much cleaner result scaling and interlacing during the same step.

Figure 3. Telling After Effects to output an interlaced file with the lower field first.

Figure 3. Telling After Effects to output an interlaced file with the lower field first.

2. Render out a 29.97i interlaced file (lower field first for SD output) using the controls shown in Figure 3.

As mentioned, I used ProRes 422 (HQ) as my intermediate file format, which should minimize loss and maximize downstream editing compatibility. I used the settings shown in Figure 4 to accomplish this, choosing QuickTime as my format, then ProRes 422 (HQ) in the Format Options dialog. Note that I didn't have to resize during output because I used a 720x480 16:9 composition, but if the composition were 1280x720, I would have had to resize during this step.

Figure 4. With output in ProRes, s'il vous plaît.

Figure 4. With output in ProRes, s'il vous plaît.

The easiest way to tell if the conversion went properly is to input the 29.97i file into a 60p sequence in Final Cut Pro, and then right arrow through the file frame by frame. If the video moves slightly each frame, you've probably got it right, and if it moves every second press of the right arrow key, you've almost certainly got it wrong. Of course, if you created a short 60p test file with timecode inserted, you'll see precisely what's going on.

Again, if you're integrating 60p footage into a 60p timeline and then rendering out to 29.97i, you won't have this problem: Final Cut Pro will correctly convert each of the 60p frames into an interlaced field in the 29.97i file. On the other hand, if you're working in a 29.97i sequence, Final Cut Pro will convert the 60p file that you insert into 30p, then build both fields from the single frame, truncating the motion. In that scenario, you can preconvert your video from 60p to 29.97i in Compressor (either directly or via a 60p sequence in Final Cut Pro) or in After Effects, and input the result into your 29.97i sequence in Final Cut Pro. I would try Compressor first, and move on to After Effects only if Compressor's output isn't to your liking.

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