Okay, it turns out I found a workaround for now, using premiere's optical flow and frame blending, but it was kind of complicated. However, it performs very well.
I'm converting 60fps gameplay to 24fps with motion blur. For those who might be interested, this is what I did:
- Have 60fps gameplay
- Have 240fps sample file with same resolution
- Have 48fps sample file with same resolution
- Drag 240fps sample to create a new 240fps sequence.
- Delete the sample and drag the gameplay footage to the 240fps sequence.
- Right click the footage and time interpolation / optical flow. This will give you a smooth 240fps version of the source gameplay
- Next, drag the 48fps sample to create a new 48fps sequence
- Delete the sample and now drag the 240fps sequence onto the 48fps sequence.
- Right click this and select frame blending for time interpolation. This will blend 5 frames together for each 240fps frame.
- Export as 24fps.
The reason I used 48fps instead of 24fps (getting 10 blended frames) is because typically for motion blur, you want it to be a "180 degree shutter" which is 1/2 of the time. Having a 48fps sequence simulates a full 360 degree shutter, so exporting that to 24fps cuts out half of the frames, simulating the more typical 180 degree shutter. However, if you want the full 360 degree shutter, as it is smoother, you can simply make the second sequence 24fps.
The reason for the sample files is unfortunately it's not possible to set sequences to weird frame rates like 240/48 manually. You can also achieve this by re-interpreting the source footage as 240/48 before creating those sequences and then setting it back to its original frame rate afterwards, but of course that's an annoying way to do that.
I don't know for sure how useful this would be for OP's situation, but it may help some people.