Your thinking is on the right path, but I think the frame rates for the project and playback are messing you up.
Think of it this way: If you place a clip in the timeline,
no matter what frame rate it's at, it will play at normal speed when you've produced it
no matter what the output frame rate is. A 10fps source clip produced to 60fps runs at the exact same speed, 1x, it just has 50 extra frames of "filler" every second to meet the output profile.
PD will simply add 5 copies of every frame until the next actual frame comes along, then it will fill the next gap with 5 copies of that frame. There's no "new" information in the filled frames, but since the player has to play 60 frames every PD "stretches" the content to fit the output.
If you have a 120fps source clip and you produce to 30fps, PDF will then discard 3 out of every 4 frames so that your clip plays at the correct speed. Obviously that's not what you're doing but I want to make sure you see that changing the project or output frame rates will
never have any affect on the speed that the video plays.
Now, to show a section of (or the entire) video in slo-mo, you need to use the Video Speed power tool to tell PD how fast or slow you want that section to play. It will do all the filling/cutting of the frames so that that section plays at 0.5x or 32x normal speed, whatever you tell it to do.
If you have 120fps source clips, PD has
lots of data to fill in the new frames with, and even if you produced to 30fps you'll have new content in every frame if you slow it down to 0.25x. Generally, 60p is the best choice for producing motion clips, and PD will take care of all the math to give you a very clear picture when you want to slow a section down.
This
*tutorial* is about the ease-in and ease-out feature, which is a nice way to transition from regular speed to slo-mo and back. This
*one* is for the Action Cam center, which shows you how to make eye-catching highlights of anything you want. Take a few minutes to watch both of these, and I think you'll have a better understanding of what PD can do and how you can use these really nice features
YouTube/optodata
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