High Quality Slow Motion with Optical Flow in Motion

Final Cut Pro 7 and earlier use a method called Frame Blending to do slow motion. This causes a visual echo effect, because it’s making up new frames by just blending together existing ones. Motion has a processing technology called Optical Flow (it’s also now built directly into FCP X, but you have to select it manually) that analyzes the motion in the shot and actually generates new frames, which looks closer to true in-camera over cranking, which is the right way to do slowmo. Sometimes, the process leaves strange warping artifacts, so it won’t work in every case, and it probably won’t work well below 30% slowmo. The basic process is to send the clip to Motion, change the processing type to  Optical Flow, let it process, then send it back to FCP.

1. Select clip with speed change already applied
2. File > Send To > Motion Project
3. Save motion project to your project folder
4. Select Window > Layers
5. Click the disclosure triangle next to Group 1, select the clip which appears beneath
6. In the window at left, go to the Inspector tab, then below, to the Properties tab, then click the triangle next to Timing at the bottom
7. Change the Frame Blending option to Optical Flow
8. Go to Window > Task List if you want to see the progress bar, otherwise wait for the spinning gear indicator at the bottom of the window to disappear
9. File > Export, export the file in the same format as your sequence in FCP. (Check sequence settings if you’re not sure)
10. Replace the clip on your timeline with the one you just exported.

Note that you can just leave the motion project embedded in the timeline and skip the export process described in step 9, but that would cause compatibility issues with Color if you plan to use it for grading later.

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