THE SHORT ANSWER
Here's the approach.
Smooth Slo-Mo uses the Best (Machine Learning) video quality setting to create intermediate frames. It requires Apple silicon and takes more analysis and rendering time than simpler retiming methods.
Apple documents an additional hardware limit for larger images: frame sizes above 4K need an M2 chip or later, and the largest supported size is 8K. A speed change normally changes clip duration and moves later clips.
See the workflow.
Starts at 16:42, Introducing Smooth Slo-MoBy Ripple Training. YouTube oEmbed confirmed the title, creator and thumbnail. The title and discovery index identify Final Cut Pro 10.8. No watched-content review, answer timestamps, transcript, duration or upload date is asserted. Playback was not tested.
Step by step.
Final Cut Pro 10.8- 01
Select the shot
Select a clip, range or group of clips in the timeline.
- 02
Apply the slow motion
Open the Retime menu below the viewer, choose Smooth Slo-Mo, then choose a preset speed.
- 03
Allow processing
Wait for the required analysis and render work. Play through the result and inspect moving edges and overlaps.
- 04
Control downstream movement
For a custom speed, use Retime > Custom. Clear Ripple if you want subsequent clips to stay in place; review which portion of the shot remains visible.
Another perspective.
Sources & version notes
Written for Final Cut Pro 10.8. Menu names and available features can differ in other versions.
Version reference: Final Cut Pro 10.8Written answer checked against the linked official documentation for Final Cut Pro 10.8. Related videos have metadata verification only; they are supplemental resources, with no verified answer-specific timestamps or software-version compatibility assertion.