Forcing motion interpolation

I am editing 1080p 29.97 footage using Resolve 17.1, and have a few shots that were inadvertently shot with a 1/25th second shutter speed. Because the shutter speed was slower than the frame rate, the resulting footage contains only 15 discrete frames per second, with each frame duplicated (thereby creating 30fps). This leads to a noticeable stutter on moving footage.

I believe I could reduce this stutter if I could make Resolve interpolate the alternate frames instead of simply using the duplicates created by the camera. However, I'm having trouble doing this. In Project Settings>Master Settings I've set "Frame Interpolation" to "Optical Flow." I've then changed the clip speed to 50%, which eliminates all the duplicate frames. But when I then set the clip speed back to 100%, Resolve simply puts back the duplicate frames, rather than creating new interpolated frames. (If I set the clip speed to something other than 100% - say, 80% - I do get interpolated frames.) Is there any way I can force resolve to interpolate frames in this situation when I double the speed of a clip?

Thanks in advance for any help!

Resolve 17.1 running on an M1 Mac Mini with Big Sur. Not sure if this makes any difference, but all of my material was shot interlaced. It was deinterlaced using QTGMC/Vapoursynth/Hybrid. I don't believe the duplicate frames on these shots are related to the deinterlacing process, since the duplicates are present when I view the original interlaced footage as well.

Actually, you want to set the clip speed to 200% to eliminate the duplicate frames.

The way I'd do this, which may not be the best way, would be to export the 200%-speed clip to an intermediate, then import it and set the clip speed to 50% with Retime Process set to "Optical Flow" and Motion Estimation set to "Speed Warp".

"Speed Warp" may require the Studio version. Also note that clips with a lot of motion blur tend to be harder to interpolate.

I would also try Sean's method.

Whoops! Yes, I meant to write set the clip speed to *200%* to eliminate the duplicate frames, not 50%. Sorry, wasn't thinking clearly.

Sean, thanks for suggesting that I export and then reimport the retimed clip before retiming it by 50% to return to 29.97 fps. This did in fact create properly interpolated frames, and the result is a lot smoother (much less stutter) than the original. So you solved my problem!

As you indicated, "Speed Warp" does require the Studio version, and I'm on the free version. I used "Enhanced Better" and the results were quite good. The main problem is a lack of sharpness, which I think this is due to motion blur in the original due to the slow shutter speed - it's just more obvious now that the stutter doesn't distract from it. Do you know what improvements I should expect to see if I upgraded to the Studio version and used Speed Warp?

Do you know what improvements I should expect to see if I upgraded to the Studio version and used Speed Warp?

"Enhanced Better" often works very well, but my experience from back in version 16 before I got the Studio version is that with certain kinds of repeating patterns you can get very weird results. You'll definitely know them when you see them. If it's an issue, "Speed Warp" will likely solve it - I haven't really seen anything so far that it hasn't handled reasonably well.

Thanks Sean! What sort of "weird results" should I be keeping an eye out for? Odd motion stutters? Moire or other artifacts?

Thanks Sean! What sort of "weird results" should I be keeping an eye out for? Odd motion stutters? Moire or other artifacts?

I had a scene with horizontal wooden slats. The camera was doing a handheld pedestal move so the slats were moving vertically down the frame. I wanted to slow it down to half speed, partly for timing issues and partly as a way to make the uneven movement a little less obvious. What happened was that the image got broken up into big pieces, almost like a jigsaw puzzle, that were not exactly aligned with each other. I've attached a screenshot that shows what it looks like. The biggest issue is that these artifacts appear for a frame or two and then disappear, which makes them really distracting.

With "Speed Warp" it looks flawless.

Sean, thanks again for the detailed reply and for taking the time to post the image. This really helps me understand what sort of artifacts to be watching out for. So far so good, I haven't been seeing any such issues with the footage I'm working with using "Better Enhanced."