FCP sharing: 120fps clips in slow motion

Atilius wrote:

I have a FCP Project where all the clips are at 120fps. It plays perfectly in FCP on my Macbook Pro, but when I share it some of the clips are in slow motion.

Where are you viewing it? In QuickTime Player, QuickLook, Photos.app, IINA, VLC?

Sequoia QuickTime Player plays middle part of high frame rate movies (seems to be ≈85 fps or more) in slow-motion.

That can be prevented by adding or editing FullFrameRatePlaybackIntent tag (*) to value 1 with:

exiftool -m -P -overwrite_original -ext mov -Keys:FullFrameRatePlaybackIntent=1 movie.mov

Or by playing such movie with Sequoia QuickLook or some app like IINA that does not honor that tag. Then the whole high frame rate movie is played in normal speed (if the device can handle that).

That tag can be set back to the "middle part slow-motion" option with:

exiftool -m -P -overwrite_original -ext mov -Keys:FullFrameRatePlaybackIntent=0 movie.mov

Or deleting that tag with:

exiftool -m -P -overwrite_original -ext mov -Keys:FullFrameRatePlaybackIntent= movie.mov

Sequoia Photos.app plays the middle part of high frame rate movies in slow motion no matter what.

So for Photos those movies must be re-encoded at a slower frame rate if slow-motion is undesirable. So export such movie as original out from Photos and re-encode with some 3rd party app. 30 fps is a good starting point because it is an even integer of 240.

For example with ffmpeg H.265 defaults and '-r 30' for 30 fps with something like (this preserves metadata date but other metadata must be copied from the original which is best done with exiftool -- ffmpeg versions 4-8 do not properly handle movie metadata):

ffmpeg -i input.mov -c:v libx265 -r 30 -crf 28 -preset medium -timecode 00:00:00:00 -tag:v hvc1 -map_metadata 0 -c:a copy output.mp4

Handbrake does about the same with its default setting (maybe force 30 fps via Video > Framerate > 30, Constant framerate).

(*) iOS/iPadOS 18 introduced QuickTime FullFrameRatePlaybackIntent tag:

"key that represents whether this movie should play at full frame rate

Some apps play movies recorded at frame rates of 120fps or higher in slow motion. If your app records high-frame-rate movies, you can add this movie-level metadata to indicate whether the movie intends to play at the full frame rate (1) or at a slow motion rate (0). Apps that play movies may use this metadata, when present, to guide their behavior."

quickTimeMetadataKeyFullFrameRatePlaybackIntent | Apple Developer Documentation

The maximum frame rate that FCP can export is 60fps. When you select a frame rate for a project in Final Cut, FC will **conform** whatever frame rate the footage is to the project's frame rate.

If you really want to export 120fps, I would recommend Motion, if you have it. However, Motion is a significantly different interface. When starting a new project in Motion, be sure to set up the frame rate AND duration information (duration can be edited/changed after the project is opened, but it will be more convenient if you can at least get close to the clip length to start with.)

Also be aware that Motion plays back at a maximum of 60fps (depending on filters, effects, and generators that might also be added to the project) but it will export a full 120 frame per second export.

Here are your export options with Motion:

Atilius wrote:

I have a FCP Project where all the clips are at 120fps. It plays perfectly in FCP on my Macbook Pro, but when I share it some of the clips are in slow motion. How do I resolve this?

I am puzzled by your post.

If I change the Project’s frame rate to 60fps it plays properly, but I really want 120fps.

Change from what?

As Fox said, there are no 120fps projects in FCP.

Please give specific details.

Unless you intend to do something else with the exported video, other than playing it back, I don't see the point of exporting at 120fps, anyway.

I think that you may be confusing input and output...

If you record a clip in "slow motion" (for example, on an iPhone), it may play normal, then slow, then normal, in the iPhone, or in Quicktime Player, but in FCP it will play at normal speed. Maybe that is what you meant.

I can't fathom how that behavior could occur in a clip exported from Final Cut Pro.

The thing is: a "slow motion" clip is just a clip recorded at a high frame rate. Final Cut Pro will play it at normal speed, but you slow it down a do a perfect slow motion using all these recorded frames.

If you don't, then, as Fox said, FCP will just "conform" it to the project frame rate.

For example, add a 120fps to a 30fps project and, by default, it will throw away 3/4 of the frames.

But if you select Automatic Speed it will play every single frame, effectively slowing it down to 25%.