(Originally from one of my video's description)
First off, i figured out how to use Twixtor without using After Effects. And Zeroth off, you just can't use Twixtor with only a part of a source video (which's common in Downfall parody making), even if you enable the Time Remap, since that shitty Twixtor used the timeline of the ENTIRE VIDEO to determine which part to be slowed, and it will not get the part of the video you wanna slow. You'll have to EXPORT that part to a new video file for it to process. And to avoid Time Remap and Keyframe bullshit, the easiest way to do that is just copy the video clip to a new sequnce, and copy it as much times as the multiplier you wanna slow, like if you want to slow Shitler down to 20% you need to make that clip repeat 5 times and then EXPORT, or you can just make the later four times blank since Twixtor only deals with the first part. AND REMEMBER TO SET THE FRAMERATE OF THE SEQUNCE AS THE SAME AS THE FRAMERATE OF THE SOURCE VIDEO, OTHERWISE YOU WILL BE FOCKED. I'll explain why later.
Second off, if the framerate of the sequnce (of the final video) is as same as the framerate of the source video (now the framerate of the aforementioned video file), you can just add it to the sequnce, apply Twixtor on it, set the speed and it's all done. Otherwise, like when your origial video like Downfall movie was 24fps and the sequnce was 60fps (why? because it's easier to make music parodies if you can control time in 1/60 sec instead of 1/24 sec), you just can't do that. Because Premiere will by default interpolate the missing frames with static frames when you drag a 24fps video into a 60fps sequnce, and when Twixtor do its magic it will consider these static frames in computing and make the resulting videos in several dynamic frames and several static frames and repeat, and the amount of static frames in a row will be SO MUCH that you'll find Shitler's motion SHATTERED. So in this case not just you need to pre-render the clip with Twixtor (and don't forget to set the sequnce right, which's right by default if you just drag the clip into a blank timeline) on and import them later, and you need to set Shitler SLOWER than what you do in a 24fps sequnce.
Third off, to make the parameters right let's do a little math: If you wanna slow Shitler by 50%, the one second in the origial movie (which has 24 frames) will become two seconds in the final video (which has 60fps * 2s = 120 frames), so in order to generate 120 frames from 24 frames you'll have to set the speed to 20% in Twixtor and make a five-times long video (which means you'll have to copy the same clips five times) file for Twixtor to process. And then when you import back that processed video, you'll have to appy it with a 250% speed, since now the 120 frames in the processed video have to be finished in five seconds (it's still 24fps), and by setting the speed to 250% you can finish it in two seconds and you'll have a SHATERLESS AND SMOOTH SHITER RANTING, which every frame of it is just like a movie originally shot in 60fps.
Of course that's some error in it, since the framerate of the Downfall movie was not 24fps actually, it's fockin' 23.975fps. So the speed might be like 250.26068821689259645464025026069% accurately, but you can just fill in 250% and FOCK IT ALREADY.
And if you don't want the frame-to-frame accuracy you can do what you normally do in Twixtor, import it back and let Premiere interpolate the rest. Just remember to pre-render the damn video in a new sequnce. And pre-rendering has another benifit: you can watch Shitler ranting in slow motion IN REAL TIME, and when you render the final video, it'll be MUCH faster. And that little shitty file can be reused when you make the next Downfall parody. The unprocessed video cilp can be considered useless right now and you can delete it to save space.