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Re: Best FPS Strategy in Final Cut?

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Joe Marler
Re: Best FPS Strategy in Final Cut?
on May 18, 2020 at 11:55:58 am

[James Kozick] "1) Should all shooting be done in 60FPS? Or just the shots you know will be used for slo mo?
2) Should all the non slo mo shots be done in 24FPS?
3) Should the FCP timeline be set to 24FPS?
4) Will importing 60FPS and 24FPS footage into the same timeline cause a problem? If so, how to avoid it?
5) Will exporting the final video in 30FPS be a problem when working with a mix of 60FPS & 24FPS?"

The basic issue is frame rates which are not even multiples cannot be perfectly rate conformed. This is typically even more difficult for higher-to-lower conversions like 29.97 to 23.98. Today we have powerful computers which can use optical flow methods, but that doesn't always work well and can create artifacts.

The simple solution is shoot all material at the final product frame rate or an even multiple of that. E.g, for a 29.97 project, shoot at 29.97 or 59.94 (often abbreviated as 30 or 60 fps).

For a 24 fps project all cameras should ideally shoot at 24 or 48 or 72 fps. Unfortunately only a few cameras can do this, e.g, Panasonic Varicam and S1H. But even the S1H cannot do that if recording ProRes RAW.

In general 60 fps material can be rate conformed to 30 very well for 1x motion and will give very smooth 1/2 speed slow motion. But if both use the "180 degree shutter rule", then it's possible the 60 fps footage may have a slightly different look due to less frame blurring. If your camera permits it might be possible to shoot 60 fps at 1/60th sec instead of the typical 1/120 sec for the 180 deg. rule.

I'm not sure how visible that is to the final viewer. Live broadcast material by ABC, ESPN and Fox are at 720p/60, whereas other networks use 1080i/30, and people usually don't notice that when they change channels.

60 fps at 1/120th will also have poorer low light performance than 30 at 1/60, and the data volume will be higher.

A conflict is created when people want both "cinematic" 24 fps *and* smooth slow motion available on all shots. This typically leads to a mix of 24 and 60 fps, which is OK for true slow motion but if the 60 fps material is needed for 1x playback it must be rate conformed. There are various algorithms for that, but none are perfect.

To use optical flow rate conforming, put your 60 fps material in a 24 fps timeline, then select that clip, then in the FCPX video inspector, scroll to bottom and under Frame Sampling select Optical Flow. Then render that clip in the timeline and examine the playback smoothness. Try that for a variety of scene types, esp. with subjects moving laterally against complex backgrounds. Evaluate for warping and smearing artifacts if using optical flow conforming, and for uneven motion cadence if not using it.

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