120 fps footage to 60 fps but keep the 120 fps look

If you want blended frames and you want to keep the speed of the playback real-time, drop you 120 FPS footage in a 24 fps comp or a 24 fps sequence in Premiere Pro, and you'll get blended frames. I don't think you'll like the result. You can also force blended frames in either PPro or After Effects right in the timeline. The time sampling algorithms produce identical results. There is some fairly good information in the User Guide that explains the differences in the frame sampling modes. The names are different but the math is basically the same. AE:

Premiere Pro:

I've got some screenshots for you. Let me explain my production planning. For these shots, I need some time changes for dramatic effect I need to slow down the footage so one second of real-time takes 2 seconds of screen-time and I need to match the motion blur of footage shot at 29.97 fps. The original footage was shot at 59.94 fps with a 359º shutter which gives me the same motion blur as a shot at 29.97 fps and a 180º shutter. Both of those shutter settings give you an effective shutter speed of almost exactly 1/60 of a second. Here is the original frame at 200% magnification playing in real-time with Frame Sampling turned on which causes me to see every other frame of the original footage because I'm sampling every other frame. I don't have the exact same shot with the bicycle in the same exact position shot at 29.97 but the motion blur would be identical.

This is what happens when you turn Frame Blending on:

Frame blending in After Effects produces the same result. If you are not doing anything else to the clip but blending the frames there is no need to move over to AE. Your work will go faster in Premiere Pro.

There is one other option: Optical Flow. This option actually tries to calculate the movement of the pixels between frames and generate the best estimation of where the pixels would be.

At first glance, you might think this is doing a better job of blending the frames but it is actually identical to the original frame. You should be able to figure out the math on that one. If there was an intermediate frame to calculate because the speed change was 123% or the sequence settings were 24 fps instead of an even multiple of the interpreted frame rate you would get a better result with Optical Flow turned on than you would with frame blending but that calculation is going to cause an increase in rendering time.

If you want the best looking footage and the best looking frame when playback is paused use Optical Flow when the frame interpretation is not evenly divisible by the sequence or comp frame rate, or if the frame rate of the sequence and the footage can be evenly divided like your 120 fps footage in a 60 fps comp you can just use Frame Sampling. If you are OK with every frame that has movement in the frame to look like it has some funky motion blur, then use Frame Blending.

I apologize for misunderstanding your original post. I didn't mean to offend. When you said you wanted the footage to look like it is 120 fps I incorrectly assumed that you wanted the best looking footage with the sharpest edges and the least amount of motion blur. I guess I missed the part where you wanted the ghosting because that simulates motion blur and 120 fps footage doesn't nave much motion blur.

The question I was asking is: "Could I possibly blend every frame with the next, therefore cutting the amount of fps to half". I want blended frames. The first thing I said was: "So I have 120 fps Videogame footage, but I'd like to upload it to YouTube". I'm aware of the fact that YouTube doesn't support 120 fps. That's why I'm here, asking this question I want to turn 120 fps footage into 60 fps footage that still looks like 120 fps. Videogames have much faster camera movement than, say, a movie, and so I guarantee that my audience will notice the smoothness of the blended 60 fps frames. You noted that if I make a composition with 60 fps, and drop in 120 fps, I won't see blended frames, but instead every other frame. ​That's what I'm trying to change​