What is the difference between applying slow-mo and simply increasing the frame rate?

Let’s say I have a 24fps clip that I want to convert to 60fps so I can play it back slow-mo on a 24fps timeline. Should I:

  • Increase to 60fps only
  • Keep at 24fps and apply 3x slow-motion
  • Increase to 60fps AND apply 3x slow-motion

Just wondering if there is any difference in the results between these options, without spending a ton of compute time to compare and contrast. Does the slow-motion option add some kind of filter that a pure frame interpolation doesn’t?

this is what I would go with

There is no difference in AI quality between slow-mo and frame rate increase.
For example, converting from 30fps → 60fps is the exact same as doing 30fps with 2x slow-mo from the perspective of the AI. You are doubling the number of frames. And those frames will be the exact same quality no matter what option you pick.

The only differences are:

  1. 30fps → 60fps and 30fps 2x slow-mo have the same number of frames, but they are played at a different speed. As would be expected.
  2. Slow-mo does not retain audio on the exported file while a frame rate increase does.

It depends on how slow you want to go.

  1. Increasing the frame rate to 60fps then playing at 1 frame per frame on a 24fps time line will give you a 2.5x slow-mo.
  2. Keeping the footage at 24fps and applying a 3x slow-mo will give you a 3x slow-mo.
  3. Increasing to 60fps and applying a 3x slow-mo, then playing the footage at 1 frame per frame on a 24fps time line will give you a 7.5x slow-mo.

However, I think both option 1 and 3 may introduce issues. Since you aren’t increasing the number of frames by an integer (whole number) multiplier, the AI filter may remove a bunch of the original frames in exchange for AI generated ones to fix frame pacing issues (I’m not 100% certain this happens, but it might).

So “for safety” I would just leave the frame rate at 24fps and simply change the slow-mo setting. It’s also more intuitive this way.

Obviously, as the number of generated frames increases, so does the possibility of artifacts becoming apparent. So be careful with how slow you go.

Notes on the Apollo AI:

I should also point out, if you plan to use the Apollo frame interpolation method, you need to be careful going above 8 generated frames. The Apollo AI can only natively do 8x slow-mo. If you exceed 8x slow-mo with Apollo, I’m not sure what happens. So if you exceed 8 generated frames, then make sure you experiment with other AI models.

Side note for Apollo, Apollo ALWAYS generates 8 frames. However, if you only wanted to generate 1 frame, then Apollo generates all 8, then discards the ones it doesn’t need. So if you’re using Apollo, and have spare disk space, then simply generating and saving all 8 generated frames allows you to play around with different slow-mo options in your video editor.

See this link for extra information on Apollo from the developers: Video Roadmap Update (March 2023)