I know there are many posts like this, but not every one has precise instructions on how to perform 60i to 24p slow motion.
- Video was shot in HDV (60i) mode, cinema mode color settings, the exposure locked with shutter speed at 1/120.
- Captured via HDVSplit
- In after effects, import the footage into the Project pane
- Right click the footage in the project pane, go to Interpret Footage > Main
- Make sure Separate Fields (Upper) is turned on and then check Preserve Edges (Best Quality Only) on
- Made a new comp by dragging the footage to the "Create A New Composition" button
- Go to Composition > Composition Settings, set the frame rate to 23.976
- Right click on the footage in the timeline, go to Time > Time Stretch... and set the Stretch Factor to 200%
From what I see, it looks like After Effects is really generating individual frames for each slowed step.
In my video there is a large master timeclock on the top and then one in the lower right, showing the exact time of the footage as it is being slowed down. (The time of the slowed footage is not exactly half that of the project time because the slowed footage file starts something like 2 seconds before the project timeline)
It works very well, is totally painless, and doesn't require the rendering or processing of any additional files.